Fused neutrals

[ses]

Hi
Just trying find reason for not allowing fused neutrals in a fuseboard if there is one
I know why its dangerous to have fused neutral in service head

A single-pole, fuse, switch or circuit breaker shall be inserted in the LINE conductor only.

OR

Automatic disconnection in the event of a fault will disconnect the supply to the LINE conductor.

 

[Guest111]

Years ago both live and neutral were fused,however if a fault causes the neutral fuse to blow then the live stays live leaving a dangerous situation.

 

[telectrix]

not just that, phil. if a N fuse blows, then all the neutral conductors on that circuit will be at 240V, as there's no VD due to 0A flowing.

 

[ses]

Thanks guys

 

[7029 dave]

not just that, phil. if a N fuse blows, then all the neutral conductors on that circuit will be at 240V, as there's no VD due to 0A flowing.

100% correct

 

[ian.settle1]

Fused neutrals have not been allowed since 1955, are you sure the neutral is fused and is not a solid link in the fuse carriers?

 

[ses]

Positive rewirables had them all out

 

[Dean Williams]

Could Tel please explain how all the neutrals would be 230v if the neutral fuse blew, i can't get my head around it. thanks

 

[jamesBoater]

Surely it would be because they have no path back to the sub station where neutral is bonded to earth?

only an apprentice so please correct me if my thinking is incorrect.

james

 

[telectrix]

OK, Dean. think of a circuit. for simplicity, L ( 230V) feeds 1 light, then from the light goes via the N back to the supply N (0V). switch the light on and the supply goes through the load in at 230V and out at 0V. there is a current flowing in accordance with ohms law.

this means that there is a volt drop across the load V=IR.

now, imagine that the N is disconnected from the supply by a blown fuse. the current flow is the zero as it's open circuit.

the VD across the load is now zero so ye have 230V all through the circuit to where the open circuit is, draw it out, it becomes obviuos.

this situation only arises when the load is connected. if it's isolated or switched off , then there's no voltage after the switch.