1 HVACR114 – Electrical for Gas Heat Fuses. 2 What is a fuse? A fuse is a simple device used to protect circuits from over-loading and overheating. Most.

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HVACR114 – Electrical for Gas Heat

HVACR114 – Electrical for Gas Heat

FusesFuses

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What is a fuse?What is a fuse?

• A fuse is a simple device used to protect circuits from over-loading and overheating.

• Most fuses contain a strip of metal that has a higher resistance than the conductors in the circuit.

• This strip also has a very low melting point.• Since it has a higher resistance, it will heat

up faster than the conductors.

• A fuse is a simple device used to protect circuits from over-loading and overheating.

• Most fuses contain a strip of metal that has a higher resistance than the conductors in the circuit.

• This strip also has a very low melting point.• Since it has a higher resistance, it will heat

up faster than the conductors.

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• When the current exceeds the rating on the fuse, the strip melts and opens the circuit.

• Fuses are one time devices and must be replaced when the strip or element melts.

• The cause for the circuit overload must be identified and corrected before replacing the fuse.

• When the current exceeds the rating on the fuse, the strip melts and opens the circuit.

• Fuses are one time devices and must be replaced when the strip or element melts.

• The cause for the circuit overload must be identified and corrected before replacing the fuse.

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Plug FusesPlug Fuses

• Plug fuses have either an Edison-base or a type S base.

• Edison base fuses are used in older installations and can be used for replacement only.

• The type S fuse can be used only in type S fuse holders. Otherwise an adapter must be used.

• Plug fuses are rated up to 125 V and 30 A.

• Plug fuses have either an Edison-base or a type S base.

• Edison base fuses are used in older installations and can be used for replacement only.

• The type S fuse can be used only in type S fuse holders. Otherwise an adapter must be used.

• Plug fuses are rated up to 125 V and 30 A.

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Dual Element Plug FusesDual Element Plug Fuses

• Many circuits have electric motors as the load or part of the load.

• Motors draw more current when starting and can cause a plain fuse to burn out or open the circuit.

• Dual element fuses are frequently used in this situation.

• Many circuits have electric motors as the load or part of the load.

• Motors draw more current when starting and can cause a plain fuse to burn out or open the circuit.

• Dual element fuses are frequently used in this situation.

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• One element in the fuse will melt when there is a large overload, such as a short circuit.

• The other, will melt and open the circuit when there is a smaller current overload lasting more than a few seconds.

• This allows for the larger starting current of an electric motor.

• One element in the fuse will melt when there is a large overload, such as a short circuit.

• The other, will melt and open the circuit when there is a smaller current overload lasting more than a few seconds.

• This allows for the larger starting current of an electric motor.

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Cartridge fusesCartridge fuses

• For 230 v to 600 v service up to 60 A, the ferrule cartridge fuse is used.

• From 60 A to 600 A, knife-blade cartridge fuses can be used.

• A cartridge fuse is sized according to its amperage rating to prevent a fuse with inadequate rating from being used.

• Many cartridge fuses have an arc-quenching material around the element to prevent damage from arcing in severe short circuits.

• For 230 v to 600 v service up to 60 A, the ferrule cartridge fuse is used.

• From 60 A to 600 A, knife-blade cartridge fuses can be used.

• A cartridge fuse is sized according to its amperage rating to prevent a fuse with inadequate rating from being used.

• Many cartridge fuses have an arc-quenching material around the element to prevent damage from arcing in severe short circuits.

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Knife- Blade cartridge fuseKnife- Blade cartridge fuse

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Circuit BreakersCircuit Breakers

• A circuit breaker can function as a switch as well as a means for opening a circuit when an overload occurs.

• Most modern houses and commercial buildings use circuit breakers.

• A circuit breaker can function as a switch as well as a means for opening a circuit when an overload occurs.

• Most modern houses and commercial buildings use circuit breakers.

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• Circuit breakers use two methods to protect the circuit.

• One is a bimetal strip that heats up with a current overload and trips the breaker, opening the circuit.

• The other is a magnetic coil that causes the breaker to trip and open the circuit when there is a short circuit or other excessive current overload in a short time.

• Circuit breakers use two methods to protect the circuit.

• One is a bimetal strip that heats up with a current overload and trips the breaker, opening the circuit.

• The other is a magnetic coil that causes the breaker to trip and open the circuit when there is a short circuit or other excessive current overload in a short time.

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Internals of a circuit breakerInternals of a circuit breaker

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