Introduction to Electricity and Fuse BasicsModule 1

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Conductors and Insulators

Plastic Insulator covering

Metal Conductor

Current Flow

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Volts and Amps

Head of water inmetres = “Volts”Litres per Second = “Amps”

Volts - Pressure

Amps - Flow

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Watts

No of Pullers (Amps) x Determination (Volts)

= Power (Watts)

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Ohms

Short Thick Pipe = Low resistance

Long Thin pipe = High resistance

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The Fuse as ‘Weak Link’

The ‘Load’ • lamp• Heater• Radio

Fuse

Cable

voltage source Current

Vs

Plug Socket

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Basic Fuse Construction

Ceramic Body

Connecting Terminals(Tags)

Elements(Strip)

Sand Filler

Caps

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Element Operation

Arc burning away ends of element

Hot ionised gas carries current between broken element ends

Sand grains are molten to form glass tube

Sand grains stick together to form ‘fulgurite’

Element wire or strip

Sand filler

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AC or DC

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DC – Direct Current

Voltage and current is “always on”

Example :- Car Battery

Volts

Current

Time

Time

AC – Alternating Current

Voltage and current is cycles positive to negative passing through zero

Volts

CurrentExample :- Domestic plug socket, Industry & commercial

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Current-Limiting Effect

HRC fuse-link interrupting fault current

Current-Limiting effect of fuse

Fuse

Short Circuit Fault

Possible fault current in the event of a major short-circuit

Operation of fuse

Earth

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Fuse Rating

• Voltage Rating

• Current Rating

• Interrupting Rating

• Watts Loss

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Common Units

Multipliers Measure

• giga

• mega

• kilo

• milli

G 1 000 000 000 (109)

M 1 000 000 (106)

k 1 000 (103)

m 0.001 (10-3)

• Potential

• Current

• Resistance

• Power

Volts V

Amps A

Ohms

Watts W

• MW MegaWatts

• m milliOhms

• kV kiloVolts

• mA milliAmps

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Characteristics

• Fuse Characteristics

• Time Current Curves

• Cut Off Curves

• I2t Values

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Time-Current Characteristics

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Time-Current Characteristics

Current (Amps)

Tim

e (S

econ

ds)

Derivation of Time-Current Characteristic

Current (Amps)

Tim

e (S

econ

ds)

10A

25A

40A

63A

Family of Time-Current curves forGiven fuse type

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I2t (Ampere2 seconds) Characteristics

Time

Potential Fault Current

Pre-Arc

Total

I

Pre Arcing I2t

Total I2t

Areas

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Cut-Off Current Characteristics

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Fuse Discrimination

Total clearing I2t of minor fuse should be less than

pre-arcing I2t of major fuse.

Major Fuse

40A

Minor Fuses Loads

20A

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Certificates

Fuses tested by third party (ASTA, KEEMA, VDE SEMKO etc).

Fuses tested to relevant standard

Fuse the issued with certificate if all tests passed.

Typical certificate issued by third party test laboratory