Is a Fan isolator required

[Dillb]

As many on here will know MI require a 3 amp fuse also on most models

Have you ever come across one fail because it wasn’t?

 

[123]

Use a decent brand like Vortice and there is no need for the 3A fuse. Silliest thing I have seen is Bathroom Lights Fused down from 5A fuse/6A MCB to 3A fuse for the fan. Totally pointless exercise.

 

[brianmoooore]

I know of a fire in a new build a few years ago, where the fire was deemed to have been caused by stuck fan blades and the lack of a 3A fuse in the fan supply. Locked rotor current insufficient to trip the 6A MCB supplying the circuit.

 

[telectrix]

I know of a fire in a new build a few years ago, where the fire was deemed to have been caused by stuck fan blades and the lack of a 3A fuse in the fan supply. Locked rotor current insufficient to trip the 6A MCB supplying the circuit.

it would probably not have blown a 3A fuse either.

 

[brianmoooore]

I would think that is exactly the reason the manufacturers specify a 3A fuse.

 

[telectrix]

they specify a 3A fuse because they don't have a clue about OCPD discrimination. a 1A fuse would be more appropriate.

i'll give you a personal example. i had a vivarium with a 250wall heat/light reflector lamp. plug fuse was 5A. when the lamp blew, it took out the 16A MCB in the CU, leaving the 5A fuse in the plug intact.

 

[brianmoooore]

Presumably the collapsing filament produced a near short circuit, otherwise nothing would have blown/tripped. Under those circumstances a type B MCB probably would trip faster than a plug fuse would rupture. The stuck fan motor would pass a sustained current of a few amps which is a completely different scenario.
On a related subject, there have been many threads on here concerning MCBs in series, and their lack of discrimination. While this may be true when short circuits are considered, a lower rated second MCB in the chain will discriminate against overload.

 

[telectrix]

we hope.

 

[davesparks]

I know of a fire in a new build a few years ago, where the fire was deemed to have been caused by stuck fan blades and the lack of a 3A fuse in the fan supply. Locked rotor current insufficient to trip the 6A MCB supplying the circuit.

Then the manufacturer should have fitted appropriate protection within the fan, the ocpds we install are not there to protect appliances, they are there to protect the cables which feed the appliances.

 

[brianmoooore]

Not sure I'd like to argue that in front of a Coroner's court.
Fortunately, in the case I referred to, no Coroners were involved, although the property in question received serious damage to its roof, and presumably, water damage throughout the rest of the house.
I normally only fit triple pole fan isolators alongside in line fans in lofts, and supply the whole lighting circuit to the bathroom through a switched FCU, fitted with a 3A fuse as per most manufacturers instructions.
Wall mounted fans, which I try to avoid because of their comparatively poor extraction rate and noise, just get the switched FCU.

 

[Andy78]

Not sure I'd like to argue that in front of a Coroner's court.
Fortunately, in the case I referred to, no Coroners were involved, although the property in question received serious damage to its roof, and presumably, water damage throughout the rest of the house.
I normally only fit triple pole fan isolators alongside in line fans in lofts, and supply the whole lighting circuit to the bathroom through a switched FCU, fitted with a 3A fuse as per most manufacturers instructions.
Wall mounted fans, which I try to avoid because of their comparatively poor extraction rate and noise, just get the switched FCU.

Not sure I'd like to be a manufacturer in court explaining why the product I had designed and sold did not have adequate protection for its design.

 

[Wilko]

Not sure I'd like to be a manufacturer in court explaining why the product I had designed and sold did not have adequate protection for its design.

Agree Andy, but it doesn't seem to stop them. Many extractor fans and dryers are still made without thermal overloads, which is strange given their proximity to dust and fluff that jams them from time to time.