00 Customer Service - NORAweb.org8-4 Basic Electricity Figure 8-1: Water analogy Chapter 8 Basic Electricity voltage pushes the electricity through the wires, it keeps it under pressure

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Basic ElectricityChapter 8

Chapter 8—Basic Electricity 8-3

IntroductionOur objective for this Chapter is to make

you feel more comfortable with electricityand to give you the information you needto service and troubleshoot electricaldevices.

The easiest way to learn about electricityis to define the words used to describeelectricity and its properties. Let’s startwith the word electricity. Electricity is an

almost magical way to take the potentialenergy locked up in coal, natural gas, oil,waterfalls, and even inside atoms—movethat energy great distances—and ultimatelyhave it do useful work for us.

Any source of electricity must get theenergy from somewhere. The battery getsenergy from a chemical reaction. Thegenerator gets energy from the work doneturning the shaft. The work it does for

Chapter 8Basic Electricity

Electrical safetyElectricity can be dangerous. It can

create three hazards: fire, skin burns, andshock. Shock can cause muscle spasms,unconsciousness and even death.

Proper installation of all electricalequipment is essential. The NationalElectrical Code® sets the standards. Localcommunities can make this code law, andin addition, they can make their own codeseven more restrictive.

A common and dangerous practice istesting the ignition transformer with ascrewdriver. The transformer is putting out10,000 volts and can give you a danger-ous and serious shock.

Electric energy needs a pathway fromthe source and back to the source. If youdo your job, this pathway is our electriccircuit.

But any wet object has enough mineralsin the water to provide an alternate path-way. The human body is over 50% water,and when the skin is damp it will providea good pathway back to the source if thereis not an easier one. Never allow yourbody to be that pathway! Always considerall electrical components to be energizeduntil you test and prove they are not.

When you are working on electricity,remove all metal objects such as watchesand jewelry from your hands and wrists.Until you are absolutely sure a circuit isshut off, only use one hand—keep theother in your pocket. This prevents theelectric pathway from going from onehand to the other hand through your heart.Be sure to replace any damaged or frayedwires, protect wires from touching movingequipment, and keep them clear of walk-ways.

8-4 Basic Electricity

Figure 8-1:Water analogy


voltage pushes the electricity through thewires, it keeps it under pressure.

Once the electricity has finished doingits work (turning a motor, making a spark),it returns to where it came from under nopressure. The voltage is all “used up”.Therefore, voltage supplied to the circuit isvoltage used by the circuit.

Amps = water flowAmperes, or amps for short, are a way of

expressing the amount of electricityflowing through the wire, the rate of flow(current). They are like the gallons perhour flow of water through a pipe.Figure 8-1.

The voltage is like the force of the waterin the pipe and the amps are like theamount of water flowing out of the faucet.

Ohms = resistance to flowAs water flows through a pipe, it

encounters resistance to the flow depend-ing upon the physical characteristics of thepipe. How much water flows through thepipe, at any given amount of water pres-sure, is affected by the size of the pipe andeven the smoothness of the inner walls.

Amps also meet resistance from insula-tion, motors, circuits or anything thatrestricts the free flow of electricity. Thisresistance to the flow of Amps is calledOhms.

Resistance to flow makes frictionand friction makes heat

Resistance to flow, whether it is water orelectricity, creates friction, and frictionconverts energy to heat. Electricity facesmuch resistance trying to fight its waythrough wiring, and it creates a lot of heatdoing it. The greater the resistance to flowin the wire, the more heat is produced. Thisisn’t all bad. The heat can be used to make

Oilheat is to power our motors that pumpoil and water, make the spark needed forignition; and automatically control theentire heating process.

Electrical current flows through wires,switches, and transformers to our heatingappliances.

The force that pushes the currentthrough the wire is called Voltage, which ismeasured in Volts. The amount of current

flowing through the wire iscalled Amperage orCurrent, which is measuredin Amps. The Resistance tothis flow is measured inOhms. The power used torun our motors and createspark is measured in Watts.

To better understand these importantwords, it might be helpful to compareelectricity to the flow of water in a pipe.

VoltsVoltage is like water pressure (pounds

per square inch), and like water pressure,does not need an actual flow. Regardless ofthe faucet being open or closed, there isstill water pressure in the pipe. Likewise,there are volts at an electrical outlet eventhough nothing is plugged into that outletand there is no flow. Of course, thepotential for flow is there and that is whyvolts are referred to as electric potential; itcould flow if the conditions were righteven though it is not flowing now.

Voltage is the force created by the powersource (the battery, transformer, or genera-tor). This is called the electromotive force(EMF).

When water comes out of a faucet, itflows under pressure. But when that waterdrains out of the sink, it has no pressureexcept gravity. Voltage is the same. As


Figure 8-2: What’s a Watt?

Did you know?Electric company bills are based

upon kilowatts per hour, kwh.A kilowatt is 1,000 watts.


The mathVolts, amps, ohms and watts are allrelated to each other. If you changeone, you change the others, too. Theserelationships are described by twomath formulas:

volts = amps times ohms

and watts = volts times amps

Remember, if one changes,it affects the others.

1 Volt

1 Amp

1 Watt

electric heaters for toasters, electric waterheaters, and electric baseboard heat. Thisheat can also be used to make heat anticipa-tors in thermostats and safety timers inprimary controls.

What’s a watt?Watts are the power consumed by an

electrical circuit. One amp (remember,that’s the amount of flow) driven by onevolt (the amount of pressure) through acircuit equals one watt of power, see Figure8-2. This work can also be called horse-power. One horsepower equals 746 watts.

If a circuit using one watt operates foran hour, this called a watt-hour. Sometimes,AC power is called volt-amps (VA) orapparent power. As current or voltageincreases in a circuit, the power consump-tion and work done also increases. Everyelectrical device needs a certain amount ofpower, so it is given a power rating basedon it being supplied with a specific numberof volts and amps. If the right amount isnot supplied, it changes the device’s powerconsumption and performance.

ConductorsSome materials offer very little resis-

tance to the flow of electricity; thesematerials are called conductors. Mostmetals are good conductors. Gold, silver,copper, and aluminum are very goodconductors. That’s why wires are made outof metal. Also, some switches are made outof mercury (a liquid metal).

Wires are the conductors; they are verymuch like pipes for water. In a water pipe,not only does the pipe material affect theresistance to flow, the size of the pipe orwire also determines how much resistanceto the flow there is. A fat wire, like a fatpipe, offers less resistance than a skinnyone, and a short wire offers less resistancethan a long one. In electricity, temperatureis important, too. Cold conductors offerless resistance than hot ones. Force isneeded to overcome this resistance. Re-member, in water, the force is calledpressure (pounds per square inch), and inelectricity, the force is measured in volts.

InsulatorsMany materials offer a lot of resistance

to the flow of electricity, these materialsare called insulators. Air, glass, porcelain,plastic, and rubber are all good insulators.They stop the flow of electricity. These


Figure 8-4:Open and closed switches


Figure 8-3:Water circuit Electrical circuits

The most important thing to understandabout electricity is the electric circuit.Electricity has to flow from a source outinto the circuit and back to the source.Figure 8-3.

A typical circuit, then, has a conductorthat carries the electric current from thesource, through a switch, to a load—andback to the source. Current flows only in acomplete circuit. However, the energy itgains in the electromotive force (measuredin volts) from the power source is lost inthe resistances (ohms) it encounters in thecircuit. The switch is a device that inter-rupts the circuit. When it is open, electric-ity can’t flow. When closed, the circuit iscomplete and the flow continues. SeeFigure 8-4.

materials are used to contain orcontrol the flow of electricity

along a conductor, such as acopper wire. Because air isa good insulator, theresistance of the air stopsthe electricity at the endof a wire like a woodenplug stuck in the end of

a pipe. If enough waterpressure is put on that plug

it will pop out and the waterwill flow. If enough electric

pressure (volts) are put against the insulat-ing air it, becomes a conductor and lets theelectricity flow in the form of a spark. Aten thousand volt transformer can makeelectricity jump across the air spacebetween the ignition electrodes in anoilburner. This creates the “spark” thatignites the oil.

LoadsA load is a device that converts electrical

energy to some other form of energy inorder to do work. A load also createsresistance that opposes electrical flow. Hereis an example: a light bulb converts electricenergy to heat and light because thefilament resists the flow of electricity,getting so hot it actually glows. Anotherexample: a motor changes electric energyinto mechanical energy.

Some of the loads found in oil burnercircuits are:

• Motors—in the burner, circulator, fan,power venter, humidifier

• Electromagnetic coils—in relays,solenoid valves

• Transformers—in ignition and control

• Heaters—in the primary control safetyswitch, thermostat heat anticipator



Figure 8-6

Fuse Switch

PowerSource Load

Figure 8-5:Fuse or circutbreakerprotects thecircut

overcomes resistance to create flow. Anychange in ohms will cause the oppositechange in amps because volts from thepower source are relatively constant. Anincrease in ohms reduces amps. A decreasein ohms increases amps. Increasing voltsincreases amps, this is called Ohms Law,Figure 8-6. It states: “It takes 1 volt topush 1 amp through 1 ohm.”

A complete circuit should alwaysinclude a load of some sort. If you just runa conductor from the source back to thesource without going through a load, youhave a short circuit. Since there is noresistance to slow up the electrical current,the amps just keep going higher and higher.This increases the heat build-up from theresistance in the conductor until it gets sohot it starts a fire.

Fuses or circuit breakers are installed inthe circuit to prevent this from happening.Circuit breakers are automatic switches thatcut off the current if it starts to reachdangerous levels. Figure 8-5.

The primary resistance to flow in acircuit is the thing doing the work, the“load”. It converts the electrical energy intoanother from of energy. However, theconductor can also restrict the flow,especially if it is undersized, too hot, or toolong.

Resistance (ohms) opposes flow. Voltage



Fuse Switch6 Amps

120 VoltsPowerSource

6 Amps

2 Amps 20 Ohms

20 Ohms40 Voltsat Each

20 Ohms2 Amps

PowerSource

120Volts

Load20 Ohms

Figure 8-8:Multiple loadsin series

Figure 8-7:Volts, ampsand ohms in acircuit

Series CircuitA series circuit is one where there is

only one path for the electric currentthrough the loads. Remember the oldChristmas tree lights (each light is a load)where, if one burned out, they all wentout? That was a classic series circuit. Asidefrom the problem of losing one load andshutting off all the rest, the other drawbackto a series circuit is that each load stealselectricity from the other loads.

In a series circuit, the power is deliveredin the greatest quantity to the point of

largest resistance. This is why poor connec-tions in a circuit, where the resistance ishigh, tend to overheat.

Since voltage applied to a circuit isvoltage used by that circuit, more than oneload in the same pathway will share thesupply voltage. Loads in the same pathwayreduce the voltage to each load as well asthe current through the entire circuit. Thevolts drop as they go from load to load.The current flow (amps) is affected by boththe volts and the total ohms of the circuit,and is the same in all parts of the circuit.

To review, in a series circuit the totalresistance (ohms) is equal to the ohms ofall the individual conductors, switches, andloads present in the circuit. The currentflowing (amps) in all parts of the circuit isthe same. By adding all the voltage dropsof all the loads together it equals theapplied voltage (volts from the source).Figures 8-7 and 8-8.

Parallel circuitA parallel circuit has separate branches

for each load. This way, if one load burnsout, it will not affect the other loads. Also,all the loads receive the same voltage.

The loads are parallel to each other. In aparallel circuit, some of the loads and notothers can be turned on. For example, theburner motor and the ignition can runseparately, so the spark can be shut offonce flame is established.

In a house circuit, all the lamps andappliances are wired in parallel. This wayeach can be turned on and off separately.See Figures 8-9B and 8-10B.

The resistance of the load in each branchcircuit determines the current (amps)delivered to that branch. The current in thecommon lines is equal to the currentflowing in the branch circuits served by



Figure 8-9:Series and parallel circuits

A = Series circuitB = Parallel circuit

Figure 8-10:

A

B

A

B

A = Series circuitB = Parallel circuit

120 Volts

120 Volts

that section of the common line. Unlike ina series circuit, the current may vary indifferent parts of a parallel circuit.

As the number of branch circuitsincreases, the total current draw increases.If you plug too many appliances into anextension cord the amp rating of the wiremight be exceeded. The wire will get hot.The overloaded circuit could cause a fire.

Overloaded circuits also decrease thevoltage to all the loads. As the wire heatsup, its resistance increases. The wire startsacting like a load in series with the otherloads, and starts stealing electricity from allthe loads in the circuit. This is why theoilburner should be wired with its ownindividual circuits, not sharing the circuitwith any other loads.

Combination circuitOilheating systems use what is called a

combination circuit. The switches and limitcontrols are in series with the primarycontrol. If any one of them opens, theelectric current to all the loads stops. Allloads are wired parallel to each other toallow individual component control and toensure full voltage is supplied to each load.

Safe capacityfor 120 volt circuits

To be sure you will not overload acircuit, check the amps needed for each ofthe loads connected to the circuit. Thisinformation is on the label of the load. Addup all the watts to be sure they are withinthe safe capacity. The rated ampacity ofcontrols, switches, and conductors must befollowed.

AC/DCElectric current is either direct current

(DC) or alternating current (AC). Directcurrent typically comes from a battery. It

only flows in one direction, from thenegative side of the battery through thecircuit to the positive side. Alternatingcurrent is what the electric companysupplies. It changes direction, flowing backand forth in the wire. Each back and forthchange is called a cycle. In North America,


Figure 8-11:L1 and L2point to thepower source


the electricity cycles 60 times a second, 120changes of direction.

The current delivers power to the loadno matter which way it is flowing. Thevoltage goes from and returns to zero 120times a second. A light bulb in an ACcircuit glows dim and bright in just thisrhythm.

In a DC system, there are two kinds ofelectrical charges—positive and negative.Positive is also referred to as “hot” andnegative as “neutral”. In an AC system, theswitched line is referred to as “hot” (H) orL1 and the unswitched side is referred to as“neutral” (N) or L2. (Be careful: L2 is alsolabeled as the second hot leg in mostelectric distribution panels. The L2 referredto here is the neutral wire.)

Separating electricity into two wires iscalled polarization. It is a way of makingsure the electricity goes where it is wanted.You have probably noticed that most smallappliances have a wide blade and a thinblade on their plug. There is only one wayyou can plug these things in. This way theappliance’s switch will control the hot wire,not the neutral wire allowing for a safeshut-off of current. If polarization isreversed in heating systems, some controlswill appear to function normally, but thelimit control will be interrupting theneutral. This is dangerous.

Wiring diagramsWiring diagrams are sort of like road

maps or blueprints that show us how acircuit is designed. To install or serviceelectrical equipment, you must be able toread the wiring diagram.

One of the confusing things aboutwiring diagrams is that a complete circuit isalways needed, and then the diagram startsright out with a big space between the twowires feeding the circuit. These two wiresare labeled + (positive or hot) and- (negative or neutral), or as mentionedpreviously, they are now called L1 and L2(line 1 and 2). All three names mean thesame thing. When you see these labels, itmeans there is a complete circuit—withoutactually drawing it.

If you follow L1 and L2 off to the leftoff the page, they go back to the circuitbreaker, the main breaker, and all the wayto the big transformer hanging on the polein front of the building. From there they goall the way back to the power plant. Justremember, the arrows on L1 and L2 arepointing at the power plant, and theyrepresent a complete circuit. Figure 8-11.

L1 is the electrically charged line thatcauses electrical flow and L2 is the returnline home. The direction of flow is fromL1 to L2—from charged to uncharged—pressurized to unpressurized.

WiresWire comes in many different sizes.

Wire sizes run from 0000 (4 naught, thelargest) to 40 (the smallest); the lower thenumber, the fatter the wire. To size a wire,consider the maximum voltage rating of thewire and the amperage draw of all the loadsin the circuit.

The number of wires bundled togetherin the wire sheathing (insulating jacket) isprinted on the sheathing after the wire


Did You Know?When the switch is open, theelectricity flows out of the powersource to the open switch. It can gono farther. In a fraction of a second,the potential on the power side ofthe switch reaches the same as thepotential from the power source,and there is no further flow ofelectricity. At the same time, thepotential on the other side of theswitch reaches the level from theother side of the power source, andthere is no current. When we closethe switch, the negative chargeinstantly goes to the positivepotential on the other side andelectricity flows through the circuit.


gauge number (14/2 and 14/3). Onlyinsulated wires are counted, so 14/2 has ablack, white, and a bare ground wire whichis not insulated and therefore not in thecount. 14/3 has an added red wire. Ther-mostat cables can have from two to sevenwires in them, depending on the addedfunctions of the thermostat (air condition-ing, humidifier, and fan functions.)

To make identification easier, the color-coding of the wire insulation is standard-ized.

The spot where wires are joined togetheror hooked to a control is the weakest linkin a circuit. Be very careful when makingthese connections. All connections must bein a junction box or protected control boxwith clamps at the entrance and exit to besure stress is not placed on connections ifthe wires are pulled.

If exposed to high heat or humidity,connections may become dirty or corroded.Always check exposed connectors (like theterminal block on primary controls), andalways seal hidden connections withelectrical tape. Copper wire is recom-mended for all oilburner wiring and isrequired in some cases.

Armored cableAny wiring around an oil-powered

appliance should be protected by eitherflexible metal conduit or armored cable.There are two kinds of armored cable: BXand MC.

BX has no ground wire. Its metalsheathing serves as the ground. Somepeople mistake the thin metal bonding stripin the cable for a ground wire. The strip iseasily broken and is used only to make aconductive connection to a metal junctionbox. Older BX used heavy steel sheathing.Aluminum is now used because it is lighter,easier to cut, and is a better conductor.

MC cable is like BX, but with a greeninsulated grounding wire. Most codesrequire MC instead of BX for a sureground.

Flexible metal conduit has no conduc-tors installed in it. The National ElectricalCode® specifies how it can be used andhow many conductors may be installed inthe conduit.

SwitchesSwitches are used to stop the flow of

electricity. It is a simple idea; just cut theconductor and put an insulator (air)between the two cut pieces of the conduc-tor.

A switch is like a drawbridge installedin the middle of a race course. Imaginewhat would happen if during a race, yousuddenly opened the drawbridge, leaving abig hole in the track. All the cars wouldstop; there would be no more current flow.Thanks to the car brakes, the resistancewould be very high but there would still bevoltage. The cars would still have all that


Figure 8-12:Switchingarrangements(various setups)


power available from the engines even ifthey were not using it.

Electric switches open to stop the flow ofelectricity just like the drawbridge opens tostop the flow of traffic. Switches can bemanually or automatically operated.

For a switch to safely control a load on atypical oilheat system, it must be located inthe source or hot line (L1), never in theneutral line! Switches in the neutral line canturn the load on and off but will not allowwork to be done on the load without the riskof electric shock.

There are many different kinds ofswitches. The most common switch is asingle pole, single throw switch, or SPST forshort. They are either on or off. This is aswinging gate (or drawbridge) that can makean air break in a conductor when it is openand connect the break when it is closed. ASPST switch turns everything in a singlecircuit on and off. There can be many SPSTswitches in one hot line.

Another type of switch is a single poledouble throw switch, or SPDT. This switchis used to turn the electricity on or off in oneor the other of two separate circuits. Thiswould be like a Y intersection. You candecide to drive on one road or the other.Some heat/cool thermostats have SPDTswitches.

Double pole single throw (DPST)switches can make or break two separatecircuits at the same time. The two circuitsbeing switched can be off the same voltageor different voltages. This would be like adrawbridge that had a street and a railroadtrack on it. The main breaker at the electricpanel is a DPST.

Double Pole Double Throw (DPDT)switches re-direct the power of twoseparate supply lines to two differentcircuits. See Figures 8-12.

The contacts of automatically operatedswitches in wiring diagrams are shown intheir normal (at rest) position when the unit


Figure 8-13:Warp switch,often used as asafety switch incontrols

Firgure 8-14:Warp switchlocking burnerout on safety


Bimetal

Spring

ResetButton

Spring

Wires

ContactBlades

Wires

Heater

Contacts

Insulators

Heater

Wires

Contact BladesWires

ResetButton

Spring

SpringContacts

Insulators

Bimetal

Figure 8-13 Figure 8-14

is not operating. Contacts on automaticallyoperated switches are classified as nor-mally open (NO) or normally closed (NC).The determination is made by the positionof the contacts when the device is either notenergized or not sensing the condition it isdesigned to sense.

Manual switches are operated by hand.Examples of manual switches in oilburnercircuits are the stair switch, the on/offswitch at the burner, the manual/auto fanand thermostat switches and the resetbutton on the primary control and motor.The reset button is an example of a manualswitch that also is switched automatically.

Automatic sensing switches respond to achange in conditions such as: temperature,pressure, flow, liquid level, light andhumidity.

Some switches open when the tempera-ture, pressure, light, or liquid level risesand some open when one of these thingsfalls. If the switch “makes” (closes) on fall,this is called “makes on fall” or “breaks(opens) on rise.” If a switch opens as aresult of a rise in the sensed condition, thisis called a direct acting (DA) switch. If it

opens on fall in the sensed condition, it is areverse acting (RA) switch.

Heat-only thermostats and high limitsare direct acting switches since they openon the rise in temperature. Cooling thermo-stats, fan off switches in fan-limit controls,low-water cutoffs, and reverse actingaquastats are reverse acting because theyopen on the fall of the sensed condition.

Timers–bimetals& warp switches

As you will learn in the primary controlchapter, one of the things an oilburnercircuit must do is shut itself off on “safety”in case flame is not established after theburner has been energized.

In many of these controls, there is atimer switch that uses small electricalheaters in combination with bimetals.Figures 8-13 and 8-14 shows how it works.

A bimetal is composed of two differentstrips of metal fused together. One end ofthe strip is secured and a small electricheater is placed under it. As it heats up, thetwo metals expand at different speeds. The


Figure 8-15:Electromagnet

Figure 8-16:Solenoid valve


one closer to the heater expands faster.Since the two pieces of metal are fusedtogether and they are secured on one end,the quickly expanding piece of metal bendsaway from the heat and makes the stripwarp. This is why it is called a warpswitch.

As you can see in the illustration, as thebimetal warps, it releases the movablecontact and the spring on the movablecontact opens the circuit. This puts theoilburner on ‘safe’ and stops the flow ofelectricity to the heater, see Figure 8-15.The only way to close this switch again isto wait for the bimetal to cool and warpback and then someone must push the‘reset’ button to reset the moveablecontact under the lip of thebimetal.

Electricity andmagnetism

Electromagnetismdescribes the relationshipbetween electricity andmagnetism. If you move awire in a magnetic field, yougenerate voltage if that wire ispart of a complete electricalcircuit. The generated voltagewill cause electric current to flow

through the wire. As electric current flowsthrough the wire, it creates a magnetic fieldaround the wire. A coil of wire creates astronger magnetic field than a straight wire.The coil is called a solenoid. If an iron corewere placed inside the coils of a solenoidand the solonoid is energized, the magneticfield created magnetizes the iron core whilethe current flows. This is an electromagnet.See Figure 8-15.

Two factors affect the strength of anelectromagnet:

1. The intensity of the currentin the coil.

2. The number of turns of wirein the coil.

Electromagnets are rated in amp-turns.

Solenoid valvesTo make a solenoid valve, an iron bar is

placed into the center of a coil of wire andelectricity is sent through the wire. Theelectromagnetic force will pull and hold thebar in the center of the coil. If a spring isattached to the iron bar (or valve stem), itreturns to its original position when theelectricity is shut off. If a valve seat is puton the end of the valve stem you have anelectrically operated valve. Figure 8-16.

Relay switchesRelays are electromag-

netic switches found inprimary controls,operating controls, andswitching relays thatuse electromagnets toopen and close. Tocreate a magnetic field,

wrap a coil of wirearound a metal core. The

magnetic field magnetizesthe core and this electric


Figure 8-17:Simple relay

Movable Contact

Spring

Electromagnet

To Control Circuit—Power Supply andSwitches

Fixed Contact

L2

L1

Load


magnet is used to open or close a switchthat is held in its normal position by aspring, see Figure 8-17.

The nice thing about this kind ofautomatic switch is that low voltage wiringcan be used for the electric magnet and theswitch that sends electricity through thecoil that can make or break a line voltageswitch. When the low voltage remoteswitch (thermostat) opens, the magnetismimmediately stops and the spring quicklyreturns the switch to its normal position.This snap action reduces arcing as theswitch opens or closes.

The biggest problem with relays is thecontacts. Dirty or corroded contacts addresistance to the circuit, resulting inreduced voltage to the load, which cancreate arcing that shortens the life of thecontacts. The good news is that most newrelays are enclosed in plastic to keep themclean. A properly working relay will notcause any voltage drop when closed.

Relays are represented in wiring dia-grams as the coil of wire and the switch.

The coil is usually energized by lowvoltage. The switch can control either ahigh or low voltage circuit. The workinglimit of the switch is determined by theamperage draw of the circuit it is control-ling. Many relays are single pole doublethrow switches, so you might have a lowvoltage switch and a line voltage switch.The way to keep track of all this is to labelthe coil with a number and a letter like 1K.Then label the switch contacts controlledby that coil 1K1 and 1K2.

TransformersTransformers use electric power at one

voltage to produce an almost equal powerat another voltage. In our industry trans-formers operate on alternating current(AC); they are made of an iron core withtwo separate wire coils wrapped aroundtwo sides. The coil where the electricitygoes in is the primary coil, and the coilwhere the electricity comes out is thesecondary coil. Figure 8-18.

Thanks to AC, the electric field in theprimary coil pulses back and forth, causingthe magnetic field it creates to pulse back



Figure 8-18:Basic design usedin an iron coretransformer

Primary Secondary

and forth in the iron core causing the northand south poles to switch back and forth.This pulsating magnet field creates apulsing electric field in the secondary coil.

Step-down transformers have moreprimary coils than secondary and reducevoltage. Step up transformers have morecoils in the secondary coil and increasevoltage. There is no electrical connectionbetween the primary and secondary coils.The only connection between the two is themagnetic field.

When voltage is applied to the primarycoil, a magnetic field is generated whichcreates voltage in the secondary coil. Theamount of voltage generated in the second-ary coil is determined by the ratio of coilsbetween the primary and secondary coils.

Transformers are very efficient and canprovide as much as 90% of the energy putinto the primary side to the secondary side.The small energy loss is due to the heatingof the wires in the coils.

Why are transformersand solenoids loads?

The greater the current, the greater themagnetic field around the conductor. The

magnetic field limits current flow bypushing back against the source voltage.

Remember, current is not only caused byvoltage from the power source, it is causedby any electromotive force that acts uponthe conductor. As the electricity goesthrough the coil of wire in the transformeror solenoid, it creates a magnetic field thatresists the flow of electricity. It becomes aload. This is called this “back emf” becauseit counteracts the voltage (electromotiveforce) from the power source.

MotorsMotors turn electrical energy into

mechanical energy.

If a permanent magnet is mounted on anaxle and placed between the opposite polesof two fixed magnets, the magnet on theaxle will spin until its north pole faces thesouth pole of the fixed magnet, and itssouth faces north. (Like poles repel eachother, opposites attract.)

If you could reverse the poles of thefixed magnets just as the rotating magnetwas coming to a stop, it would force it toturn another half circle until the oppositepoles lined up again. Figure 8-19.

If you make the fixed magnets electro-magnets every time the alternating currentin the electromagnet changes direction thepoles in the magnet flip (north becomessouth and south becomes north) driving therotating magnet around again. It will keepturning as long as the current in the fixedmagnets keep flipping. The fixed (station-ary) electromagnets are called the stator,and the rotating magnet the rotor.

Measuring electricitySince electricity can not be seen (except

for sparks), testing and measuring devicesare needed in order to properly trouble-shoot heating and air conditioning systems.



Figure 8-19:Arrangementsof magnets tocreate motion

To measure voltage (volts), amps (current),and ohms (resistance), you can buy adevice called a multimeter that lets you testall three. Your meter will come withdirections on how to use it. Read andfollow those directions.

Using a multimeterThe handiest device for electric testing

is the multimeter mentioned above. It canmeasure voltage, current and resistance.You can buy analog meters that use aswinging needle to give you continuouslyvarying readings, or a digital meter thatgives readings with discrete numbers on ascreen. Digital meters are easier to read anddon’t need to be “zeroed out” before use.

If you are reading a stable DC or ACvoltage or current, a digital meter is a goodthing. If you are measuring a slowly,varying current or voltage, a digital metercould be constantly refreshing itself,making the display very hard to follow.

Before you can use your meter, youmust decide what you want to measure (i.e.voltage, current or resistance) and what

reading (range of value) you expect to get.This way, you can pick which function touse and which scale setting within thatfunction. To prevent damage to the meter,do this before connecting the meter.Switching the function selection dialwhile attached to a live circuit coulddamage your meter. Always discon-nect the test leads or shut off the circuitbefore changing the selection dial.

Each function has a maximum andminimum range. Exceeding the maximumis dangerous to you and the meter. Thecloser you are to the middle range, themore accurate your reading will be. Pickthe range on the multi-position rotaryswitch that gives you the most accuratereading while not exceeding the maximumfor the range. If you are not sure, alwaysstart with the highest range and work yourway down.

Read your meter’s instructions todetermine what the symbols on the dialmean. The black lead should always beconnected to the COM (common plug)jack. The position of the red lead varies


Figure 8-20


L1

L2

Volts,OpenSwitch

VoltageDrop

L1

L2

Volts,ClosedSwitch

with the different functions based on thesymbols marked on your meter.

• Be careful how you treat your meter

• Protect it from moisture and hightemperatures

• Replace worn or cracked test leads

• When not in use store it in its case

• Check the battery for corrosion

• Remove the batteries for long storageperiods

• Do calibration checks against knownvolts, amps, and ohms regularly

Measuring voltageA voltmeter is used to measure the

difference in electric pressure between twopoints. Since a load creates a difference inelectric pressure (or force) as it does work,

the pressure is relative; that is, one pointmust be measured against another.

Electrical charge flowing from anypower source is at a high energy level;when it returns from the circuit, its energyis low. The power source’s job is to boostthe energy level of the charge. The voltme-ter measures this change in charge (thedifference in energy level) through thecircuit.

Somewhere in the circuit, the energy ofthe flowing charge is converted into otherforms by the load. When a light bulb is lit,the electric energy becomes heat and light.To measure this conversion of energy(change in charge), use a voltmeter. Figure8-20.

Remember, “Voltage applied is voltageused.” Whatever voltage is applied to acircuit will be used up by that circuit. Thisis why measuring voltage is the best way tofind out if a circuit is working properly.

A voltmeter allows very little current togo through it. It has very high resistance,so it has almost no effect on the circuitbeing measured. When you connect theleads from the voltmeter to two differentpoints in the circuit, it measures thedifference in potential (volts) betweenthose points. It tells you how much energyis being used between the points where thetwo leads are touching the circuit.

To measure voltage, touch the one of thevoltmeter’s leads to each of the two wireson either side of the load. This willmeasure the voltage drop of that load.Voltage drop is the amount of electricalenergy that is being converted by that load.If you touched the meter leads to L1 andL2, you would measure the voltage step-upfrom the energy source.

There will be no voltage drop across aclosed switch. The pressure drop across an



Figure 8-21:Clamp-onammeter

Figure 8-22

Clamp-on Ammeters(Each Load is 100 ohms)

120 Volts

L1

L2

open switch will be the applied pressure ofthe power source.

A voltmeter measures the difference inelectrical pressure or the potential differ-ence in emf between two points in contactwith the test leads. Voltmeters are used inparallel to whatever is being tested.

The two things to remember whentesting for voltage on a live circuit are:There has to be resistance between the twopoints being measured and there must be acomplete circuit to make a zero readingmean something.

Measuring currentAn ammeter measures the rate at which

the electric current flows from the powersource, through the wire and load, and backto the source.

There are two kinds of ammeters; in-lineand clamp-on. In-line ammeters are notcommonly used by service technicians inour industry. They are primarily usedduring bench testing.

The clamp-on ammeter is easy to use. Ituses electromagnetic induction. Wheneverelectricity flows through a wire, it creates amagnetic field around that wire. Theclamp-on ammeter converts the strength ofthe magnetic field into a current reading.

To use a clamp-on ammeter, first pickthe correct scale (when in doubt start high)then open the jaws of the meter, insert oneline between the jaws, close the jaws andtake a reading. This meter can be usedsafely on a live circuit without disconnect-ing the power since the magnetic field isnot affected by the wire’s insulation. SeeFigures 8-21 and 8-22.

Clamp over one line at a time becausethe magnetic fields from each wire canceleach other out. If you placed both the hot

and neutral lines between the jaws youwould get a zero reading even if there wascurrent flowing in the wires. You can testeither the hot or neutral line, but not bothat the same time. Since AC and DCcurrents create different magnetic fields, besure to set your meter for the current youare measuring.

If the current you are measuring is toolow for your meter to read accurately, youcan loop the wire around the jaws severaltimes to increase sensitivity. Just divide thereading by the number of loops. Ten loopsis an easy number to use.


Figure 8-23:Ohmmeterreadings


No resistance(short)

Measurableresistance

Infiniteresistance (open)

To understand what your ammeter ismeasuring, you should know:

• The type of circuit

• The design ampacity (current carryingcapacity) of the components

• The design current draw of the loads.

The design ampacity is usually markedon each component and must be higherthan the amp rating of the fuse protectingthat component. For example, a 15-ampfuse should protect components exposed to120 VAC.

The design current draw of a load isusually listed on the rating plate. The listeddesign current draw, in amps, is for steady-state normal operation. On start-up andunder increased motor load, there is ahigher required torque and a sloweroperating speed, the motor current will behigher.

The surge current draw on initial start-up of a motor may be four or five times itsnormal current draw. Sometimes the surgecurrent draw is also listed on the ratingplate.

If a burner motor bearings are dry, or theoil pump has rust in its gear set, the motor

will not be able to function normally andthe current draw might be less than thelisted rating.

Measuring resistanceThe ohmmeter is used to measure

resistance. It measures the resistancebetween two points. It can measure just oneload or a whole circuit.

The ohmmeter has its own electricsource (a battery). Since it provides its ownpower, disconnect the circuit or device tobe tested from the power source. It mea-sures the resistance between two points byapplying a steady voltage from the meter’sbattery to a de-energized circuit or device.Figure 8-23.

You can use the ohmmeter to see iftheres is a complete circuit. This measure-ment is called continuity. If you touch oneohmmeter lead to a wire disconnected fromthe power source going into a circuit and,at the same time, touch one of the leads tothe wire coming out of the circuit and thereis no current returning to the meter, itmeans the pathway between the two wiresis broken.

The ohmmeter will read infinite resis-tance and there is no continuity. If, on theother hand, 1 amp of current returns forevery volt applied to the circuit, there is noresistance. The ohmmeter will read zero.This is a short circuit. Any reading betweenzero and infinite is the resistance to flowfor the circuit measured.

Unlike the voltmeter and ammeter, theohmmeter must never be connected to alive circuit. It supplies its own power fromits battery, and it will be damaged if outsidecurrent goes through it.

To use the ohmmeter, disconnect thepower supply and isolate the line or device



Figure 8-24:Commonohmmeter readingerror, isolate theload to be tested

Figure 8-25: Safelydischarging acapacitor

L1

L2

LoadActuallyTested

Broken LoadYou Wanted

to Test

putting out 10,000 volts and that can giveyou a dangerous and serious shock. Alwaysuse proper test equipment.

Be sure to verify that all capacitors arefully discharged before touching orworking on them. To safely discharge acapacitor you will need a 20,000 ohm 5watt resistor, two insulated screwdriversand two jumper wires with alligator clipson both ends. Figure 8-25. Connect onejumper wire clip to one wire of the resistorand clip the other jumper wire to the otherresistor wire. Connect the clips on the

being tested from other paths back to thesource. Do this in case there is a capacitor(a device that stores electricity) in thecircuit.

The ohmmeter must be zero adjustedbefore every test. Just touch the two testleads together creating a short circuit withzero resistance and use the zero adjustmentdial. Most digital meters automatically zeroadjust. If your meter will not read zero, thebattery is too weak and must be replaced.

To test for resistance, disconnect L1 andL2 (H and N wires) from the power sourceand touch the two leads on either side ofthe component to be tested. If there is noresistance the reading will be zero. If thereis no connection between the two points theresistance will be infinity. The digital meterwill read OL (overload). A reading betweenzero and the maximum scale setting is theresistance between the connected points.

Not only must you isolate the circuit tobe tested from the source, it must also beisolated from the rest of the circuit. Other-wise, you will get a false reading from theresistance of another load in a branchparallel circuit. Figure 8-24.

Electrical safetyElectricity can be dangerous. It can

create three hazards: fire, skin burns, andshock. Shock can cause muscle spasms,unconsciousness and even death.

Proper installation of all electricalequipment is essential. The NationalElectric Code® sets the standards. Localcommunities can make this code law, and inaddition, they can make their own codeseven more restrictive.

A common, but dangerous practice, istesting the oilburner ignition transformerwith a screwdriver. The transformer is


The lowerthe wire

number, thebigger the

wire and themore amps it

can carry.


Testing Review

Voltmeter:Touch one lead from the meter to one side of the load or circuit to be tested and one to

the other so the meter is parallel to what you are testing. This test is done on a live circuit.The reading is the difference in voltage from the spot where one lead is touching to thespot where the other is touching.

Ammeter: Now, energize the circuit and the meter will tell you the amps traveling to that load

or circuit. The clamp on ammeter is much easier and less intrusive to use. Close theclamp around the single wire you wish to test while the circuit is energized and it will tellyou the amps flowing through that wire. The meter will read the amps through the wirecover, so this test need not be done on bare wire.

Ohmmeter:Disconnect the hot and neutral wires from the power source and discharge any

capacitors that may be in the circuit to be tested. The ohmmeter supplies its own power.Touch the leads from the meter to the wires you have disconnected from the powersource and the meter will show the resistance of that circuit or load.

opposite ends of bothjumper wires to differentscrewdrivers, hold thehandles of the screwdriversand touch the blades toopposite terminals of thecapacitor.

Electric energy needs apathway from the sourceand back to the source. Ifyou do your job, this

pathway is our electric circuit.

Any wet object has enough minerals inthe water to provide an alternate pathway.The human body is over 50% water, andwhen the skin is damp it will provide agood pathway back to the source if there isnot an easier one. Never allow your bodyto be that pathway! Always consider allelectrical components to be energized untilyou test and prove they are not.

When you are working on electricity,remove all metal objects such as watchesand jewelry from your hands and wrists.Until you are absolutely sure a circuit isshut off, only use one hand—keep the otherin your pocket. This prevents the electricpathway from going from one hand to theother hand through your heart. Be sure toreplace any damaged or frayed wires,protect wires from touching movingequipment, and keep them clear of walk-ways.

FireEvery wire has resistance and converts

some electrical energy into heat. Whencurrent flows, the wire warms up and keepsgetting hotter until it reaches steady statewhere the heat it loses to its surroundingsequals the heat being created. If there is toomuch current being drawn by the loads in acircuit, the steady state temperature of the

Multimeter Tips



wire may be dangerously hot, creating afire. This is called an overloaded circuit.

Common causes of overloads are: • Too many devices on the circuit

• Devices working harder than theyare supposed to

• Damaged or worn out devices

• Current surge when a motor starts

A short circuit causes a sudden exces-sive draw well beyond the capacity of thecircuit. It happens if the resistance of theloads is removed, or there is a directunrestricted current flow to ground,conductors touching grounded metal, or thesource conductor is touching neutral.

Fuses and circuit breakersTo protect against any circuit carrying

too much current, every circuit needs a fuseor circuit breaker. It is wired in series so allthe current in the circuit goes through it.These are automatic switches that open ifthe current goes higher than their rating.

Fuses are one time only devices. Whenthey blow, they must be replaced. Circuitbreakers can be reset and used repeatedly.Never used an oversized fuse or circuitbreaker; this defeats the purpose of the fuseor breaker and may create a dangeroussituation. You should find out why thecircuit is drawing too many amps, causingthe fuse or breaker to open.

Shock protectionThe electric shock from a 120-volt

circuit is dangerous and can be fatal. Ashock occurs when a person becomes partof an electric circuit. The severity of shockdepends upon:

• Amount of current

• Type of voltage (AC or DC)

• The path the electricity takes throughthe body

• Amount of voltage

• Time duration of the shock

• Condition of the skin

To protect from shock, electricity mustbe kept in the wire. Install the circuits sothat in case the electricity escapes, it doesno harm.

A shock is when an electric currentpasses through the body, causing spasticcontraction of muscles. If it goes throughthe heart, it may kill.

Shocks happen when you touch a wirecarrying lots of volts and some other partof your body is touching something atground potential. Bare feet, especiallywhen wet, are very dangerous. A dryhuman body is pretty resistant to electricflow, but a sweaty or otherwise wet one is avery good conductor. Rubber soled shoesinsulate your body from ground andprevent the formation of a complete circuit.

Good insulation keeps the electricityinside the wire, but insulation may crackwith age or high temperature and may alsowear off if it is touching a moving part. Soeven if it was wired right at first, with ageit may go bad and let electricity leak out,presenting a shock hazard.

To be sure that the electricity has an easyway to get home without going throughyou, install a ground fault protectionsystem (GFI- Ground Fault Interrupter).Grounding provides a direct low resistancepath from the circuit to ground.



For example, suppose the insulation onthe wire inside a burner motor cracks andthe wire is touching the motor case. If youkneel down on a damp floor to work on theburner and you touch the motor with yourhand, the current could flow through yourbody into the floor, and over to the groundrod from the house service—a completecircuit. This is a dangerous situation. Tostop this from happening, run a ground(bare copper or green) wire from the burnerback to the ground rod.

This pathway will offer much lessresistance to the electricity than your bodyand the cellar floor and the current will gothat way. Electricity is lazy; it will alwaysgo the easiest way, the path of least resis-tance. Figure 8-26.

All electric codes including the NEC—National Electrical Code®—call for carefulgrounding. Connections from one wire toanother must be enclosed in insulation.Every switch, outlet, and appliance must beprotected. All these devices should beconnected to each other by grounding wiresconnected to a rod driven 10 feet into theearth. The ground wire is the third prongon plug-in devices.

To protect us, the ground wire must gofrom the load back to the panel without anybreaks. The best way to check this is totouch one lead from your voltmeter to theeither the hot or neutral wire and one to theground wire. If the ground is good you willget the same reading as you would fromhot to neutral.

Stay on the lookoutfor potential problems

When troubleshooting a circuit, electricjunction boxes often must be opened. Thiscan be dangerous. Sometimes wires frommore than one circuit might be hiding in a

box. If you can, try to trace all the wiresgoing into the box to see if more than onegoes back to the service panel. The goal isto shut off all the electric wires going tothat box before removing the cover.

If this is not possible then treat the wiresin the box as if they were hot. Whileholding the cover plate, use an insulatedscrewdriver to carefully loosen the screwsand ease off the plate. To test for power,use only one hand to gently pull out thewires so all connections are at least an inchapart. Unscrew the wire nuts and use yourmeter to test for voltage.

Watch out for overcrowdedjunction boxes

Too many wires jammed into too smalla box can cause shorts.

• Check for old and cracked insulation.

• Confirm polarization. White wires goto silver terminals. Black goes to brass. Besure there is only one wire hooked to eachterminal.

• Check armored cable connectors. Thecut end of the metal cable can be sharp. Toprevent the wire insulation from being cutbe sure protective plastic bushings areinstalled at the cable ends.

Safety tipsThe Occupational Safety and Health

Administration’s (OSHA) electric safetyregulations require that anyone doingelectrical repairs must receive safetytraining. They also require that employersmust adopt safe electrical work practicesand that a lock out tag out must be used forhard-wired equipment that is de-energized.

The key to safety is to know the dangersof electricity and how to avoid hazards.


Figure 8-26




Lock outtag out

should remove locks and tags is the personwho put them there.

To do a lock out tag to OSHA’s satisfac-tion, a lockout device and tag stating not toremove the lock should be placed over thecircuit breaker, fuse box, or switch that willprevent a person from energizing thecircuit.

It is difficult to put a lock on a stairswitch. As an alternative to locking out apiece of equipment, tag outs can be used ifit will provide an equivalent level of safety.

OSHA indicates that shutting off theequipment in two places will provide suchequivalence. For example, if you shut offthe circuit breaker and emergency switch atthe top of the stairs and stick a note on bothof them you have met the requirement.

The following are some safety tips:• Shut off the power!

• Stay focused! Even after turning offthe power, work as if the wires are live.

• Post a sign on the electric panel andremote switch so no one will turn on thepower while you are working on the circuit.

• Always check to be sure that theequipment being used is grounded.

• Always use insulated tools and be surethe insulation is in good condition. Useelectrical tape on wire nuts and connec-tions for added protection.

• Water on the floor is a good conduc-tor—when working in wet areas, be sure touse protective equipment like rubber-soledshoes.

• Do not overload electrical circuits.

• Use extra caution with extensioncords. Their insulation can be cut, and theycan be overloaded leading to increaseddanger.

• Inspect heating equipment beforestarting repair to be sure it is de-energized.

• When inspecting a circuit, keep onehand in your pocket to prevent hand-to-hand shock.

Lock out tag outThis procedure is used to be sure that no

one turns on a switch and energizeselectrical equipment while you are workingon it. Use a tag or lock connected to theswitch or circuit breaker to let other peopleknow you turned it off on purpose and youwant it to stay off. The only person who



Figure 8-27:Wire nut

Figure 8-28:Strap andwrap wire

Obviously this procedure is veryimportant if the circuit breaker and remoteswitch are in different rooms than theequipment you are working on. You do notwant some helpful person thinking theyfound the problem with the heater andturning on the breaker in the other roomwhile you are hooking the black wire fromthe primary control to the L1 wire.

Practical tipsSplicing wires

To splice wires first strip the wires witha wire-stripping tool. (Don’t use a knife; itmight nick the wire, reducing its electriccarrying capacity.) Slip the wire into thecorrect hole in the stripper, squeeze, twist,and pull off the insulation.

Next hold the stripped wires togetherand grab the ends with lineman’s pliers.Twist clockwise, making sure all wiresturn. Twist them together like a candy caneinto a neat looking spiral. Now snip off the

end leaving enough exposedmetal so the wire nut willjust cover it. (About a halfinch is good.) Now slip onan appropriately rated wirenut as far as it will go andturn it clockwise untiltight, Figure 8-27. Finallywrap electrical tape around

the bottom of the nut and wires.

Hooking wires to a terminalBefore you start, many devices come

with the terminal screws unscrewed. Screwin any terminal screws for terminals youare not going to use. Now you are ready tohook up your wires.

Strip about three quarters of an inch ofinsulation from the wire end. Then usinglong nose pliers grab the wire just abovethe insulation and bend it back at about a45-degree angle. Move the pliers upabout a quarter inch from theinsulation and bend again in theopposite direction about 90degrees to start a loop. Nowmove the pliers another quarterinch and bend the wire into aquestion mark”?”. Leave anopening in the end just bigenough for the terminalscrew. (You can buy a wire-bending screwdriver tomake this job easier.)Figure 8-28.

Make sure the terminal screw is un-screwed far enough, and then slip the loopover the screw threads, with the looprunning clockwise. Use the long nose pliersto squeeze the loop around the terminal,and then tighten the screw.

You should never attach two or morewires to one terminal screw. To make amultiple connection, make a “pigtail” wireby cutting a six-inch length of wire, stripboth ends, splice the multiple wires to oneend, and then attach the other end to theterminal screw.

Armored cableTo cut armored cable, bend it about one

foot from the end and squeeze the benduntil the armor breaks apart slightly. If youhave trouble, use a pair of channellocks tosqueeze the wire. Figure 8-29.


Figure 8-29:Cuttingarmored cable


• Electricity must have a complete pathfrom an electrical source through a load andback to the source.

• Conductors offer less resistance to electriccurrent than insulators.

• Voltage is the electrical pressure differencebetween two points in a circuit that causeselectricity to flow.

• Current is the rate of flow as measuredin amps.

• Resistance is the opposition to flowmeasured in ohms or pressure drop.

• A load offers resistance to an electrical current.It determines the current draw for any voltage applied.

• The load will only draw enough current toovercome that resistance.

• Voltage applied is voltage consumed.

• It takes one volt to push one ampthrough one ohm.

Basic Concepts about Electric Circuits

TwistClockwise

Snip andRemove,

Trim SharpEnds

Bend andSqueeze

Bonding Strip

Bushing

Cut Here

Grasp the cable firmly on each side ofthe break and twist the waste end clockwiseuntil the armor comes apart enough for youto slip in cutters. If you have trouble doingthis with your hands, use two pairs ofpliers.

Cut through one rib of the armor with apair of side-cutting pliers. Slide the wastearmor off the wires. Remove the paperwrapping and plastic strips. Leave the thinmetal bonding strip alone. Use side-cutpliers to trim away pointed ends of thesheathing that could nick a wire.

The next step is to slip the plasticbushing over the wires. Slide itdown into the armor so it protectsthe wires from the sharp edges ofthe armor. If there is a bondingstrip, cut it to about two inches andwrap it over the bushing and aroundthe armor to ensure conductivecontact between the armor and thebox.

Option: If you plan to do a greatdeal of wiring, you might want tobuy an armored wire cutter to speedup this job.

Now attach the clamp (connector) to thecable. Remove the lock nut from the armorcable clamp and slide the clamp down overthe bushing as far as it will go. Thentighten the screw.

Finally remove the knockout from thejunction box, and poke the wire andconnector into the hole. Slide the locknutover the wires, and thread it onto the cableclamp. Use a hammer and screwdriver totap the locknut tight.


field. Some of the electrons are at the back of the end zone.The electrons have almost no mass, but they carry anegative charge equal to the positive charge of the proton.So a neutral atom has as many electrons in the spacesurrounding the nucleus as it has protons inside it. Theelectrons are held close to the nucleus by the electric forceof attraction between opposite charges.

In different kinds of atoms, the electrons farthest from thenucleus may be bound strongly or weakly. The ones thatallow their electrons to escape easily are called conduc-tors. The atoms that hang on tight to their electrons areinsulators.

The flow of free electrons in a conductor is what we callelectric current. If you throw a switch to turn on a lamp fivefeet away, it takes 40 minutes for the little electrons to fighttheir way through the conductor from the switch to the lamp.What turns on the lamp right away is a pulse, each electronpushing those ahead of it until the pulse reaches the lamp.The pulse travels almost at the speed oflight.

If you are feeding the lamp withAC, it is not a pulse that travels buta wave. Each electron vibratesback and forth, passing its energyalong to the next, just like moleculesof air passing a sound wave or waterin the ocean passing a wave.

In case you are interested

In this chapter we have talked about what electricitydoes. We have not really covered what it is. That isbecause electricity can be confusing. However, some ofyou might be wondering what electricity actually is. So forthose brave souls who want to know more, read on. If youare already hopelessly confused, you can stop readingnow.

Everything contains electrically charged particles, bothpositive and negative. These particles make up the atomsthat are the building blocks for everything in the universe.Atoms are really, really small. It would take several millionof them, lined up, to reach across the dot at the end of thissentence. Each atom is electrically neutral because itcontains equal amounts of positive and negative charge.

The positive charge of an atom is in the center, calledthe nucleus. The nucleus is made of protons that have apositive charge and neutrons that have no charge. Thenumber of protons determines what kind of material theatom is. For example, hydrogen has one proton, andoxygen has eight.

Circling around the outside of the nucleus are elec-trons. They are sort of like planets circling around the sun.As in the solar system, there is a lot of empty space. Thenucleus is like a marble sitting in the middle of a football


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00 Customer Service - NORAweb.org8-4 Basic Electricity Figure 8-1: Water analogy Chapter 8 Basic Electricity voltage pushes the electricity through the wires, it keeps it under pressure