ABB Power T&D Company Inc.Relay DivisionCoral Springs, FL 33065

LL. 41-553.2B

TYPE BL-1 THERMAL OVERLOAD RELAYFOR CLASS IE APPLICATIONS

CAUTION: Before putting relays into service,remove all blocking which may have been insertedfor the purpose of securing the parts during ship-ment, make sure that all moving parts operatefreely, inspect the contacts to see that they areclean and close properly, and operate the relay tocheck the settings and electrical connections.

APPLICATION

These relays have been specially designed andtested to establish their suitability for Class 1 Eapplications. Materials have been selected andtested to insure that the relays will perform theirintended function for their design life whenoperated in a normal environment as defined by

0 ANSI standard C37.90-1978, when exposed toradiation levels up to 1 O4 rads, and when subjectedto seismic events producing a Shock ResponseSpectrum within the limits of the relay rating.

“Class 1E" is the safety classification of theelectric equipment and systems in nuclear powergenerating stations that are essential to emergencyshutdown of the reactor, containment isolation,cooling of the reactor, and heat removal from thecontainment and reactor, or otherwise are essen-tial in preventing significant release of radioactivematerial to the environment.

The type BL-1 relay is used primarily for ther-mal overload and instantaneous overcurrentprotection of motors and generators, but it mayalso be used for the protection of transformers orany other apparatus if the temperature-rise under

overload is similar to that of motors. The thermalelement is the “replica type” and has a time-current characteristic closely approximating theaverage moderate overload heating curves ofmotors. Its characteristics prevent the protectedequipment from being subjected to overloads ofsuch magnitude or duration as, to cause them toreach dangerous temperatures, but at the sametime permit the utilization of the inherent thermalcapacity of the apparatus.

As its operation depends upon the rate of heatgeneration in a heater element within the relay, itmay be used for either ac or dc application. It isordinarily connected in the secondary circuit of asuitable current transformer in ac applications.Since the voltage drop across the relay must bewithin a range of about 0.49 to 0.88 volts at fullload on the protected machine, customary shuntsrated in millivolts are unsuited for dc applications.However, the drop across a portion of theprotected circuit, such as the interpole field win-ding of a machine, sometimes can be utilized as asource of energy for the relay,

CONSTRUCTION AND OPERATION

The double element type BL-1 relay Figures 1& 2 contains two heater units, two indicating in-stantaneous trip units I I T an indicating contrac-tor switch (ICS), and a slow dropout telephonetype relay.

THERMAL UNIT

The thermal unit consists of a housing of mold-ed material which encloses a coiled thermostatic

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All possible contingencies which may arise during installation, operation, or main-tenance, and all details and variations of this equipment do not purport to be coveredby these instructions. If further information is desired by purchaser regarding hisparticular installation, operation or maintenance of his equipment, the local ASEABROWN BOVERI representative should be contacted.

SUPERSEDES I.L. 41-553.2A DATED FEBRUARY, 1979CHANGED SINCE PREVIOUS ISSUE. EFFECTIVE DECEMBER, 1985

TYPE BL-1 RELAY I.L. 41-553.2B

design can be fully utilized. A high permeabilityreactor is provided in shunt with the heaters for acapplication. This reactor has no effect on the timecurve of the relay up to 1000% of pointer setting,but provides additional protection for extremelyhigh currents of short duration. The reactor shouldbe removed from the circuit for dc application.This is readily accomplished by removing theheavier lead from the two left hand terminals ofeach thermal unit.

The contacts are silver and are of the bridgingtype so that flexible leads are unnecessary. Themoving contact consists of a silver plate con-structed so that it can pivot on its mounting and beself-aligning with the stationary contacts. Thestationary make contacts are supported in moldedinsulation fastened to a plate which can be rotatedaround the shaft by means of a gear sector on itsedge and a pinion attached to the scale pointer.This serves to expand the scales and permit in-creased accuracy of setting.

Stationary break contacts are provided. Theseare similar to the make contacts and are mountedon a second rotatable plate in front of the platewhich supports the make contacts. This plate isheld in position by spring pressure, but can bemoved to any desired position with reference tothe make contacts. A scale on the supportingplate for the make contacts is used in locatingthe break contacts at a definite position. Rotationof the make contacts by means of the scalepointer does not change in the spacing betweenthe make and the break contacts. When no alarmcircuit is used, these break contacts are not con-nected electrically but are adjusted to provide abackstop for the moving contact. When an alarmcircuit is used, these break contacts are connectedelectrically to control the Auxiliary Time - DelayUnit.

lndlcatlng Contactor Switch Unlt (ICS)

The dc indicating contactor switch is a smallclapper type device. A magnetic armature, towhich leaf-spring mounted contacts are attached,is attracted to the magnetic core upon energizationof the switch. When the switch closes the movingcontacts bridge two stationary contacts, com-pleting the trip circuit. Also during this operationtwo fingers on the armature deflect a spring

located on the front of the switch, which allows theoperation indicator target to drop.

The front spring, in addition to holding thetarget, provides restraint for the armature and thuscontrols the pickup value of the switch.

lndlcatlng Instantaneous Trlp Unlt (IIT)

The instantaneous trip unit is a small acoperated clapper type device. A magnetic ar-mature, to which leaf-spring mounted contacts areattached, is attracted to the magnetic core uponenergization of the switch. When the switch closes,the moving contacts bridge two stationary contactscompleting the trip circuit. Also, during the opera-tion, two fingers on the armature deflect a springlocated on the front of the switch which allows theoperation indicator target to drop.

Taps on the coil and a core screw accessiblefrom the top of the switch provides the adjustablepickup range.

Auxlllary Time-Delay Unlt (T) - When Used

This is a slugged telephone type relay with twosets of form “c” contacts. Only one set of contactsare used and they are connected as either Form“a” or as Form “b” contacts. The relay is normal-ly energized through the “break” contacts of theBL Units and while energized, Form “a” contactsare closed or Form “b” contacts are open. Whenthe T unit is deenergized either by the BL breakcontacts opening or by a loss of dc supply, theForm “a” T contacts will open or the Form “b” Tcontacts will close in approximately 115 ms afterhaving been energized at 125 volts dc ratedvoltage.

CHARACTERISTICS

THERMAL UNIT

The type BL-1 relay is designed for use in ap-plications where the current transformer ratio issuch that with 100 percent of full load on theprotected machine the relay will receive a currentwithin the limits of 2.5 to 5.0 amperes. For fullload currents within this range, the relay can be setto operate in accordance with the characteristiccurves shown in Figs. 3 and 4. Note that there arethree initial current conditions shown in eachfigure: O%, 70% and 100% of pointer setting. Thecurves are based upon having the initial current

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TYPE BL-1 RELAY

percent of a 3.75 ampere full load current will benear or somewhat to the left of the 3.5 amperescale marking.

It is not expected that these faster operatingcurves will be used for general application. Theyare presented to show how the relay characteristicsmay be modified to meet special conditions. Sincethe pointer position must be determined by test, itcould be located to give a time other than 15minutes at 125 percent overload. If the time werebetween 15 and 60 minutes, an approximateoperating curve could be estimated by interpola-tion between Fig. 3 and 5.

Fig. 6 is similar to Fig. 5 but shows fastertime-overload curves for full load currents thatrequire the use of the shorting link.

It will be observed that the curves of Figs. 3and 4 are approaching an asymptotic position at125% of full load, and that the Figs. 5 and 6 arefarther from their asymptotic position at 125% offull load, as would be expected because of theshorter time delay. Prior conditions of load(between zero and full load) will not affect thevalue of current that will uitimately close the relaycontacts, but variables such as friction and dis-crepancies in calibration prevent precise locationof the asymptotic value. However, after makingsome allowance for such variables, a value of 118%of full load current can be considered as the max-imum current that will not produce eventual clos-ing of the relay contacts when settings are made asdescribed for Figs. 3 and 4. For settings made perFigs. 5 and 6 this current value will be 110% of fullload.

Figs. 7 and 8 show resetting times for the typeBL-1 relay for the shorting link opened or closed.The complete resetting time is considered to be thetime measured from the moment the relay currentis interrupted until the contacts return to the posi-tion they would occupy for the steady state condi-tion of 100 percent of full load current. This com-plete time composed of the time required for thecontacts to part and the time for them to travelback to 100 percent position and separate curvesare shown for these two components of the com-plete time. The time will vary depending uponwhether the overload occurs after the motor hasbeen carrying 100 percent load or from a coldstart, and curves are shown for the two conditions.The curves are shown for a relay setting at eitherend of the adjustment range, and intermediate

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values may be obtained by interpolation.

The ambient temperature compensationprovided in the type BL-1 relay causes itsoperating time for a given current to remain ap-proximately the same regardless of changes in theambient temperature at the relay. If the ambienttemperature at the motor location varies, themotor of course will carry a higher overload safelywhen the ambient temperature is low. However, areplica type relay cannot respond to the ambienttemperature compensating means and unless it ismounted either adjacent to the motor or, if at adistance, in a location where there is assurancethat the ambient temperature will vary in exactlythe same way as at the motor. This condition fre-quently cannot be met. Also, the relay temperatureat the operating point should be very close to thatof the motor at its maximum safe operatingtemperature. The type BL- 1 relay was designed fora minimum operating temperature much lowerthan the safe operating temperature of a motor,but with a similar rate of rise when the rise is ex-pressed as a percentage of the total change in therelay temperature. This was done to obtain a lowrelay burden and to increase the amount ofoverload that the relay can carry without injury.With the low operating temperature of the typeBL- 1 relay, it would not be satisfactory to block orrender inoperative the ambient temperature com-pensation, as even moderate changes in ambienttemperature would cause appreciable changes inthe relay operating time.

The instantaneous unit used in the type BL-1relay has three taps covering a range from 6 to 144amperes. The core screw must be adjusted for thedesired trip current within a given range.

The Indicating Contactor Switch (ICS) Unitnormally supplied in the type BL-1 relay will pick-up at 1.0 amperes direct current.

CONTACT RATINGSControl Control Capacity in Amperes

Unit Voltage Will Break Will Close

HeaterHeater

0 HeaterInstan-taneous

125 Vdc 0.8 3.0 t250 Vdc 0.6 3.0 t120 Vac 5.0 5.0 t

125 Vdc 1.5 30.0 ttInstan-

0 taneous 120 Vac 30.0 71

TYPE BL-1 RELAY I.L. 41-553.2B

t These values apply where the contactor switchis not used to seal around the heater unit con-tact or contacts. For tripping duty, the heater

IIT UNIT

unit contacts can close 30 amperes at 125 or 250volts dc if these contacts are sealed around bythe ICS units.

tt The IIT unit contacts will carry 30 amperesfor 1 second.

Set the element for a pick-up current slightlyabove the maximum current which the apparatusmay receive in normal service, as for example, thestarting current of motor or the magnetizing in-rush current of a transformer. The proper tap mustbe selected and the core screw must be adjusted tothe value of pick-up current desired.

ICS

Three different operate level ratings areavailable.

The nameplate data will furnish the actualcurrent range that may be obtained from the IITunit. It is recommended that the IIT be set on thehigher tap where there is a choice of tap settings.For example, for a 20 ampere setting use the 20 to50 tap rather than the 6 to 20 tap.

Trip Circuit Constants

0.2 ampere dc rating 8.5 ohms dc resistance1 .O ampere dc rating 0.37 ohm dc resistance2.0 ampere dc rating 0.10 ohm dc resistance

IIT

Time of operation of the IIT unit at twicepickup is 35 milliseconds or less.

CAUTION: Since the tap block connector screwon the IIT unit carries operating current, be surethat the screw is turned tight. To avoid opening thecurrent circuits under load, do not change tap posi-tion without first opening the case mounted testswitches starting with the red handle switch first.Close the red handle switch last, after all tapchanges have been completed, to put the relayback into service.

INSTALLATIONBL HEATER UNIT

The relays should be mounted on switchboardpanels or their equivalent in a location free fromdirt, moisture, excessive vibration and heat.Mount the relay vertically by means of the fourmounting holes on the flange for the semi-flushtype FT case. The mounting screws may be utiliz-ed for grounding the relay. External toothedwashers are provided for use in the locationsshown on the outline and drilling plan to facilitatemaking a good electrical connection between therelay case, its mounting screws and the relay pan-el. Ground Wires should be affixed to the moun-ting screws as required for poorly grounded or in-sulating panels. Other electrical connections maybe made directly to the terminals by means ofscrews for steel panel mounting.

For the usual case, setting the thermal elementinvolves only locating the scale pointer at a posi-tion corresponding to the full load secondarycurrent of the protected equipment, and opening orclosing the shorting link depending upon whetherthe pointer is being set in accordance with the up-per or the lower scale markings. The relay thenwill have the characteristics shown in Figs. 3 and 4.This method of setting the relay for various fullload currents affords greater flexibility in applica-tion and precision in setting than is provided bymulti-tapped heater units or by interchangeableheater units of various ratings.

For detail information on the FT case refer toI.L. 41-076 for semi-flush mounting.

SETTINGS

It is desirable to have a time-current heatingcurve for the protected equipment, or to know thelengths of time that the equipment will standseveral different values of overload. These timeshould be as high or higher than the relay times forthe same load and overload conditions, as shownby Figs. 3 and 4.

There are two settings to be made on the relay. For full load currents which lie between anyThey are the IIT Unit and the BL Heater Unit. two values marked on the scale, the pointer can be

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TYPE BL-1 RELAY

moved to a readily estimated intermediate positionwith negligible error. Even if the pointer were leftat the nearest scale marking the maximum devia-tion in pointer position from the actual loadcurrent would be only 2.5% at the 5.0 ampere set-ting, increasing’to 5% at the 2.5 ampere setting.The scale lengths will vary somewhat in differentrelays due to variations in the thermally sensitivesprings. However, some movement of the pointerwill be possible counterclockwise from the 3.5ampere point or clockwise from the 3.75 amperepoint, so that for a full load current between 3.5and 3.75 amperes the scale pointer can be set in acorresponding position without appreciable error.

If the safe operating time of the equipment atsome high value of overload should be less than thecorresponding relay time, and if the instantaneousunit cannot be set as low as this value of overload,either some additional relay must be used toprovide a shorter operating time at this overloadbut with a pickup setting higher than the lesseroverloads, or the type BL- 1 relay must have its set-tings changed for faster operation. This rarelyshould be necessary, but if it is required the contactsetting must be determined by test. It would be un-dersirable to complicate and confuse the scale byadding markings for special operating conditions,and the added calibrating time would increase thecost of the relay unnecessarily. Also, no singlespecial condition would be likely to occur morefrequently than others.

Figs. 5 and 6 illustrate the reduction inoperating time obtained by decreasing the contacttravel, but these curves also show that the time atlow overloads is reduced by a much greater percen-tage than the time at high overloads. Since ingeneral this will prevent the overload capacity of amotor at low overloads (which probably will occurmost frequently) from being fully utilized, thecharacteristic curves should not be lowered morethan necessary below those of Figs. 3 and 4.

If it is determined that the relay should be setby test to obtain faster operation, it should beallowed to stand de-energized for several hours ifthe check is to made from a cold start. The covershould be on the relay when the check is made, ofcourse. It is recommended that the check be made

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at 125 percent of the current setting, or that thispoint be included in case more than one overloadis checked. Set the adjustable break contacts totheir preferred position before setting the pointerin its final position. After energizing the relay forthe required time with required value of overload,which should be carefully regulated or adjustedthroughout the run, the pointer should be movedclockwise until the adjustable contacts just touchthe moving contact. Due to a slight amount of playin the gear ing, i f the pointer i s movedcounterclockwise until the contacts just part, itsposition may differ slightly from its position whenmoved clockwise until the contacts just touch. Thecalibration points on the scale are determined bymoving the pointer clockwise until the contactsjust touch and the same procedure should befollowed when making subsequent setting.

The adjustable break contacts control the slowdropout telephone type relay “T”, when suppliedwhich can be used to prevent re-starting a motoruntil some desired time interval has elapsed afterthe motor has been disconnected due to overload.By setting the break contacts close to the makecontacts, they can be used to initiate an alarm onopening, thus giving warning of the existence ofan overload before the motor reaches a temper-ature at which it should be disconnected (by themake contacts) and possibly permitting readjust-ment of the load so that it does not become nec-essary to disconnect the motor. A scale having tenmajor divisions and fifty minor divisions is pro-vided on the plate on which the make contactsare mounted. The scale is intended as a positionreference only and has no affixed relation toopening times.

“Preferred Position of Break Contacts”

The vertical edge of the plate for mounting themake contacts should be positioned between thefourth minor division from the right and the firstmajor division of the scale. See Fig. Il. This set-ting will provide “make” contacts with a seismicfragility of greater than 5.9g ZPA as defined inIEEE Standard C37.981978. It will also providesufficient force between the break contacts atrated load to enable an external alarm or preventlogic to work properly. The break contacts are notseismically rated.

TYPE BL-1 RELAY LL. 41-553.2B

The vertical edge setting may be set for a largercontact gap but should not be set for more than sixminor divisions if the break contacts are to be in aclosed position at full load.

External diagram in Fig. 9 show several com-binations for applying these units.

ADJUSTMENT & MAINTENANCE

The proper adjustments to insure correctoperation of this relay have been made at the fac-tory. Upon receipt of the relay no customer ad-justments, other than those covered under“SETTINGS” should be required.

ROUTINE MAINTENANCE

All relays should be inspected and checkedonce a year or at other time intervals as dictated byexperience to assure proper operation. Generally avisual inspection should call attention to anynoticeable changes. A minimum suggested checkon the relay system is to close the contacts manual-ly to assure that the breaker trips and the targetdrops. If an additional time check is desired, passtest current through the relay and check the timeof operation.

All contacts should be periodically cleaned. Acontact burnisher #182A836HOl is recommendedfor this purpose. The use of abrasive material forcleaning contacts is not recommended, because ofthe danger of embedding small particles in the faceof the soft silver and thus impairing the contact.

ACCEPTANCE CHECK ANDCALIBRATION

ICS ACCEPTANCE CHECK

Refer to test diagram shown in Fig. IO.Connect an adjustable dc current source to relayterminal 4 as shown with a jumper type connectionmade inside the relay. Connect the jumper to theright hand (facing the front of the relay) stationarycontact of the ICS located in the lower right posi-tion.

Close switch S1 and pass sufficient dc currentthrough the trip circuit to close the contacts of the

ICS. This value of current should not be greaterthan the particular ICS nameplate rating. The in-dicator target should drop freely.

Repeat above except to pass 85% of ICSnameplate rating current. Contacts should notpick up and target should not drop. Open switchS1 when checking is completed.

ICS CALIBRATION

Use the following procedure for calibrating therelay if the relay has been taken apart for repairsor the adjustment have been disturbed. Thisprocedure should not be used unless it is apparentthat the relay is not in proper working order. (See“Acceptance Check”).

Initially adjust unit on the pedestal so that ar-mature lingers do not touch the yoke in the resetposition. This can be done by loosening the moun-ting screw in the molded pedestal and moving theICS in the downward position.

1. Contact Wipe: Adjust the stationary con-tacts so that both stationary contacts makewith the moving contacts simultaneouslyand wipe l/64” to 3/64” when the armatureis aganist the core.

For double trip type units, adjust the thirdcontact so that it makes with its stationarycontacts at the same time as the two maincontacts or up to 1/64" ahead.

2. Target: Manually raise the moving contactsand check to see that the target drops at thesame time the contacts make or up to 1 / 16"ahead. The cover may be removed and thetab holding the target reformed slightly ifnecessary. However, care should be exer-cised so that the target will not drop due to aslight jar.

3. Pickup: Unit should pickup at 98% of ratingand not pickup at 85% or rating. Ifnecessary the cover leaf springs may be ad-justed. To lower the pickup current, use atweezer or similar tool and squeeze each

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TYPE BL-1 RELAY

leaf spring approximate equally by applyingthe tweezer between the leaf spring and thefront surface of the cover at the bottom ofthe lower window.

If the pickup is low the front cover must beremoved and the leaf springs bent outwardequally.

Open Switch S1 when testing is completed.

IIT ACCEPTANCE CHECK

The IIT Unit requires a higher level of currentfor testing than is required by the BL thermal unit.Fig. 10 shows connections by which the IIT unitsmay be checked without passing current throughthe BL unit. When applying current in excess of 50amperes to test the IIT the current should not beleft on while adjusting it to the trip level. Instead,apply the current in short burst, not more than 2seconds long, to check for tripping. Make ad-justments in the current controls while the currentis off.

High currents left on for excessive time periodscan result in the softening and possible melting ofinsulation on the interconnecting wires.

Connect a 60 Hz current source to relay ter-minals 6 and 8 as shown. Switch S3 is connectedby a jumper to the upper left IIT tap screw. SwitchS4 is connected by a jumper to the lower left IITtap screws. Close S3 to check the upper left IITclose S4 to check the lower left IIT Open theswitch when check is complete.

The core screw which is adjustable from thetop of the trip unit and the tap located on the topof the IIT determine the pickup value. The tripunit has a nominal ratio of adjustment of 1 to 24.

The indication should occur within l/16”before, or at the same time, the contacts make.

The moving contact should provide l/64” to3/64” wipe of the stationary contact. This shouldprovide a minimum of 3 grams contact pressurewith the armature held against the core.

Apply sufficient current to operate the IITThe operation indicator target should drop freely.

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IIT CALIBRATION

Use the following procedure for calibrating therelay if the relay has been taken apart for repairsor the adjustments disturbed. This procedureshould not be used until it is apparent that therelay is not in proper working order (See “Accep-tance Check”).

Initially adjust unit on the pedestal so that thearmature fingers do not touch the yoke in the resetposition. This can be done by loosening the moun-ting screw in the molded pedestal and moving theIIT in the downward direction.

1

2.

3.

Contact Wipe: Adjust the stationary con-tacts so that both stationary contacts makewith the moving contacts simultaneouslyand wipe l/64” to 3/64” when the armatureis held against the core. This can be ac-complished by inserting a .0125 thicknessgauge between the armature and core andadjusting the stationary contacts until theyjust touch the moving contacts.

For double trip types adjust the third con-tact until it makes with its stationary con-tact at the same time as the two main con-tacts or up to l/64” ahead.

Target: Manually raise the moving contactsand check to see that the target drops at thesame time the contacts make or up to I/ 16”ahead. If necessary, the cover may beremoved and the tab holding the targetreformed slightly. However, care should beexercised so that the target will not drop dueto a slight jar.

Pickup: Place tap screw in the 6 to 20 tapand turn the core screw all the way in. Con-tacts should pickup between 5.1 and 5.7amperes. If pickup is above this range itmay be reduced by using a tweezer orsimilar tool and squeezing each leaf springapproximately equally by applying thetweezer between the leaf spring and thefront surface of the cover at the bottom ofthe lower window. If the pickup is belowthis range it may be increased by removingthe front cover and bending the leaf springs

TYPE BL-1 RELAY I.L. 41-553.2B

outward equally. An approximate adjust-ment would be where the end of the leaf spr-ing is in line with the edge of the moldedcover.

The desired pickup is obtained by setting thetap screw in the proper range and adjustingthe core screw.

“T” TELEPHONE TYPE RELAY CHECK

The T unit has a copper slug located on thecore at the end away from the clapper type ar-mature. This construction provides a fast-pick-upand a slow-drop-out characteristic. The purpose ofthis unit is to “ride through” momentary openingsof the BL break contacts which might occur duringvibrating conditions which might be produced dur-ing a seismic event.

Connect relay terminals 5 and 10 to a 125 Vdcsource as shown in Fig. 10. Close switch S2 andobserve that T contacts connecting relay terminals2 and 3 change state. Open S2 and observe that Tcontacts return to their deenergized condition in105 ms to 125 ms.

HEATER UNIT

The assembly and adjustment of the thermalunit requires alignment fixtures and other specialtools, as well as special test equipment for locatingthe position of the compensating spring assemblyon the shaft and determining the calibrationpoints. Any dismantling or alteration of the ad-justments should be avoided, as this may result inexcessive bearing friction or calibration errors.However, the construction and overload capacityof the thermal unit is such that very littlemaintenance should be required.

The resistance of the heater and the IIT set for6-20 range measured at the case terminals, shouldbe within 10% of 0.25 ohm when the shorting linkis open and 0.20 ohm when the link is closed.

The moving contact should rotate withoutnoticeable friction, and when displaced manuallyand released it should return to its original posi-tion. The shaft should have about 0.010 inch end

play.

If the calibration of the thermal unit is to bechecked at one or more points, the precautionsmentioned in previous sections should be observed.Testing should be done with the relay in its caseand the cover in place, and preferably with the casemounted on a switchboard panel. If the relay timeis to be checked from a cold start, the relay shouldhave been de-energized for several hoursbeforehand. If the overload is to be applied follow-ing a constant load, the current must be main-tained at the constant initial value until there is nofurther change in the moving contact positionbefore applying the overload. Both the load andoverload currents must be carefully regulatedthroughout the test. The relay should not be sub-jected to drafts or sudden changes in temperatureduring the test, as there is some delay in theresponse of the temperature compensation. In thefactory calibration the relay is held in a controlledtemperature and other precautions are taken tominimize factors which would introduce calibra-tion errors.

The test current should be interrupted as soonas the contacts close in order to avoid possibledamage to the heaters, particularly when testing athigh values of overload.

RENEWAL PARTS

Repair work can be done most satisfactory atthe factory. However, interchangeable parts can befurnished to the customers who are equipped fordoing repair work. Completely assembled andcalibrated thermal elements can be furnished, butindividual parts for the thermal element should notbe ordered since factory fixtures and equipmentare necessary for satisfactory assembly andcalibration. When ordering parts, always give thecomplete nameplate data.

ENERGY REQUIREMENTS

The burdens of the BL heater unit and the IITunit are listed separately below. Total impedancemay be determined by adding the two together forthe settings selected.

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TYPE BL-1 RELAY I.L. 41-553.2B

SHORTINGLINKS (OPEN

THERMAL UNITS

SCALE POINTERS

Figure 12. BL-1 Relay-front view.

1919