Fitting an extractor fan with 3A fuse

[Msitekkie]

I am in the process of fitting an in-line extractor fan (ACM125T) that requires a 3A fuse, for a utility room. Vent-Axia have advised That I do need a fused spur, from either the lighting circuit or the ring main circuit (as well as a fan isolator switch).
They also said "the switched live does not need to go through the fused spur, as this is fed to a galvanic isolation on the PCB which separates it from causing harm to the unit".

My easiest option is to take the fused spur from the upstairs lighting circuit (the fan is fitted in the chimney stack in the loft space), but the light switch in the utility room is on the downstairs lighting circuit, so in either scenario it seems to me I would end up with a shared neutral.

Although less convenient, it seems to me that I should take the fused spur from the downstairs lighting circuit to avoid a shared neutral, or am I missing something? I note other discussions on similar topics that I found did not mention the "galvanic separation". Although this separation suggests no current can flow to the other part of the circuit meaning the neutral associated with the permanant live could not be reached anyway... I should mention the Fan is a SELV unit with no earth wire.

 

[Taylortwocities]

Your live, neutral and switched live must come from the same source (circuit).

Personally see no point in having an FCU with a 3A fuse in it if the fan is fed from a lighting circuit with a 6A MCB.

In fact, the instructions only show an FCU for the basic model
There is no FCU in the diagram for the timer model.
ACM100-ACM200 F&W Instructions

Re:

I should mention the Fan is a SELV unit with no earth wire.

SELV? Really? I do not think so. Double insulated, maybe... but SELV nah!

 

[Pete999]

I am in the process of fitting an in-line extractor fan (ACM125T) that requires a 3A fuse, for a utility room. Vent-Axia have advised That I do need a fused spur, from either the lighting circuit or the ring main circuit (as well as a fan isolator switch).
They also said "the switched live does not need to go through the fused spur, as this is fed to a galvanic isolation on the PCB which separates it from causing harm to the unit".

My easiest option is to take the fused spur from the upstairs lighting circuit (the fan is fitted in the chimney stack in the loft space), but the light switch in the utility room is on the downstairs lighting circuit, so in either scenario it seems to me I would end up with a shared neutral.

Although less convenient, it seems to me that I should take the fused spur from the downstairs lighting circuit to avoid a shared neutral, or am I missing something? I note other discussions on similar topics that I found did not mention the "galvanic separation". Although this separation suggests no current can flow to the other part of the circuit meaning the neutral associated with the permanant live could not be reached anyway... I should mention the Fan is a SELV unit with no earth wire.

Double insulated but SELV not a chance

 

[Msitekkie]

In fact, the instructions only show an FCU for the basic model
There is no FCU in the diagram for the timer model.

Interesting! The diagrams are completely different to the copy of the installation instructions l downloaded about a week ago for the same model fans, which show the fuse for both basic and timer models. The stock reference Nos have also changed (but not the models). There must have been a recent revision to the ACM range.

 

[Msitekkie]

Double insulated but SELV not a chance

Was sure l had read that somewhere, but can't find it now so maybe was another of their models.

 

[Msitekkie]

Personally see no point in having an FCU with a 3A fuse in it if the fan is fed from a lighting circuit with a 6A MCB.

Other people have mentioned the same thought in earlier discussions so l queried the point with Vent-Axia. Their reply was "I'm afraid the fused spur is a requirement and is there to protect the installation".

Others have also pointed out that we have to follow the manufacturers instructions to comply with standards.

 

[bigspark17]

Yes you should follow MI and fit 3amp fuse or there warranry would void should the fan go up in flames. Click do a great range of interchangeable modules that can incorparate a 3pole fan iso and a fuseholder on a 3g faceplate.

 

[Taylortwocities]

This one is handy
Excel 3 Pole Fused Fan Isolator Switch - White | QVS Electrical Wholesalers - http://www.qvsdirect.com/excel-3-pole-fused-fan-isolator-switch-white

 

[Msitekkie]

Thanks for the suggestions, l didn't realise fan isolator switches were available that incorporated a fuse.

Vent-Axia seem to have gone quiet since I flagged the shared neutrals point with them. As it turns out I have actually got the newer version of the fan as per the instructions Taylortwocities found (thanks!) & no 3A fuse required after all on the timed version. The new diagram shows all 3 wires coming from the ceiling rose to the 3 pole isolator, but this of course assumes one is using a looped in system. My existing junction (old style) junction box is rather full so thinking to use one of those Surewire maintenance free junction boxes.
Just trying to tie up the loose ends here for anyone looking at this thread in future.

 

[Rpa07]

This one is handy
Excel 3 Pole Fused Fan Isolator Switch - White | QVS Electrical Wholesalers - http://www.qvsdirect.com/excel-3-pole-fused-fan-isolator-switch-white

I ordered a couple on the recommendation of the forum and worked a treat and neat to the eye as well. Got one in stock. Whilst ordering I bought a battery checker/bulb/fuse et al and I love it. Had a bunch of batteries that I wasn't quite sure whether dead, half dead. I've had a good time routing out the wheat from the chaff. Thanks forum!