Extractor Fan Isolator Switch????

OwainDIYer · 22 Jan 2013

JohnW2 said:
OwainDIYer said:

About the only way round it that I can see is to use a DP light switch, one pole switching the light and the other pole switching the fan trigger. The light not via the FCU, and the fan trigger, fan live and N through the FCU.

Click to expand...

How could you get "the fan trigger, fan live an N through the FCU"? At best, only one of the two L's would be fused.

The fan live, and N are direct from the FCU.
The fan trigger is from the FCU through one pole of the DP switch.

The light live and N are direct from the lighting circuit and not through the FCU.

[code:1] +------------------------------------------------------+
| |
N FAN |
LIGHT SL PL N--------------------------------+ |
L | | | |
| | +---------fan perm live---------+ | |
| | | | |
| | | | |
| | | | |
| +-----SW1a-------------------------+ | |
| | | |
+-------------SW1b--+ L N |
| +-------+ |
| | load | |
| | FCU | |
| | supply| |
| +-+---+-+ |
| | | |
+----------------------+ | |
| | |
L N |
| | |
| | |
| +-------+
| |
v v[/code:1]

JohnW2 · 22 Jan 2013

OwainDIYer said:
The fan live, and N are direct from the FCU. The fan trigger is from the FCU through one pole of the DP switch. The light live and N are direct from the lighting circuit and not through the FCU.

Ah, right - I misread/misunderstood what you wrote - apologies. Yes, that would work. However, given that we're talking a bathroom, the light switch is likely to be a pull one. One might therefore end up having to use a 45/50A one designed as a shower isolator (are they OK with frequent operatiom?), since I doubt one would easily (if at all) be able to find any other type of DP pull-switch.

Kind Regards, John

Electrifying · 22 Jan 2013

bernardgreen said:
You are not seeing the reason for the isolator are you.

If the fan comes defective or a hazard and HAS to be isolated then without a 3 pole isolator the only way to remove the hazard is to turn off the lighting circuit at the CU. Do you want ( can you allow ) your tenants to live in a house with no lights until the fan is repaired.

I was always under the impression that the reason for a seperate fan isolator was so that if the fan needed to be worked on, it could be done without having to isolate the lighting - which would obviously be an issue if the bathroom didn't have a window.

The 'Electricians Guide to the Building Regs' actually states the requirement for seperate isolation of a fan if the bathroom doesn't have a window......it doesn't mention there being a requirement otherwise.

JohnW2 said:
If you used the DP switch of an SFCU to switch the two L's, then the N wouldn't be switched - hence not true isolation.

Kind Regards, John

There is no requirement to isolate the neutral conductor in a TN system. (537.1.2)

lordwoody · 22 Jan 2013

Electrifying said:
bernardgreen said:

You are not seeing the reason for the isolator are you.

If the fan comes defective or a hazard and HAS to be isolated then without a 3 pole isolator the only way to remove the hazard is to turn off the lighting circuit at the CU. Do you want ( can you allow ) your tenants to live in a house with no lights until the fan is repaired.

Click to expand...

I was always under the impression that the reason for a seperate fan isolator was so that if the fan needed to be worked on, it could be done without having to isolate the lighting - which would obviously be an issue if the bathroom didn't have a window.

The 'Electricians Guide to the Building Regs' actually states the requirement for seperate isolation of a fan if the bathroom doesn't have a window......it doesn't mention there being a requirement otherwise.

There is no requirement to isolate the neutral conductor in a TN system. (537.1.2)

That is what I was led to believe also.

Scoby_Beasley · 22 Jan 2013

JohnW2 said:
One might therefore end up having to use a 45/50A one designed as a shower isolator (are they OK with frequent operatiom?), since I doubt one would easily (if at all) be able to find any other type of DP pull-switch.

Kind Regards, John

I believe MK and Crabtree do/did pull cords in the region of 15Amp. Pig ugly if I recall though!! (Used one in an outhouse years ago).

SaladFingers · 22 Jan 2013

Electrifying said:
bernardgreen said:

You are not seeing the reason for the isolator are you.

If the fan comes defective or a hazard and HAS to be isolated then without a 3 pole isolator the only way to remove the hazard is to turn off the lighting circuit at the CU. Do you want ( can you allow ) your tenants to live in a house with no lights until the fan is repaired.

Click to expand...

I was always under the impression that the reason for a seperate fan isolator was so that if the fan needed to be worked on, it could be done without having to isolate the lighting - which would obviously be an issue if the bathroom didn't have a window.

The 'Electricians Guide to the Building Regs' actually states the requirement for seperate isolation of a fan if the bathroom doesn't have a window......it doesn't mention there being a requirement otherwise.

JohnW2 said:

If you used the DP switch of an SFCU to switch the two L's, then the N wouldn't be switched - hence not true isolation.

Kind Regards, John

Click to expand...

There is no requirement to isolate the neutral conductor in a TN system. (537.1.2)

It's a good idea to have the ability to isolate any equipment that's fixed, for reasons outlined in other posts.

JohnW2 · 22 Jan 2013

Electrifying said:
I was always under the impression that the reason for a seperate fan isolator was so that if the fan needed to be worked on, it could be done without having to isolate the lighting - which would obviously be an issue if the bathroom didn't have a window.

In the absence of any official explanation, one has to speculate. What you say certainly makes sense, and one would think is probably at least part of the explanation, but Bernard's point about being able to take a faulty fan off-line so as to allow lighting to work until the fan can be replaced/mended is another, oft-quoted (and 'reasonable') reason. AFAIAA, the regs themselves don't contain a specific requirement for fan isolators - so it's generally manufacturers who impose the requirement (without explanation of the reason). However, if you consider the 'reason' mentioned by Bernard, then ...

Electrifying said:
JohnW2 said:

If you used the DP switch of an SFCU to switch the two L's, then the N wouldn't be switched - hence not true isolation.

Click to expand...

There is no requirement to isolate the neutral conductor in a TN system. (537.1.2)

That's true in terms of the regs isolation requirements, but if there were a N-E fault in the fan (and, hopefully, an RCD protecting the circuit), inability to isolate the neutral would mean that the lighting could not be used until the faulty fan had been disconnected. [In any event, there are TT installations

].

Kind Regards, John

AdamCH · 22 Jan 2013

Depending on where the fan is you could use one of these:

View media item 55629
http://www.astra247.com/11197/Elect...Pull-Apart-Flow-Connector/20A-4-Pin-Standard/

SaladFingers · 22 Jan 2013

AdamCH said:
Depending on where the fan is you could use one of these:

View media item 55629
http://www.astra247.com/11197/Elect...rt-Flow-Connector/20A-4-Pin-Standard/[/QUOTE]

Hmmm, depends on where it is, as you say. Even if inline, may cause some faffling about in the dark to go into a loft or mess around with removing grilles and ducting to get to any connections through ceilings.

Electrifying · 22 Jan 2013

Would you concede that anything that could go wrong with the extractor fan in the bathroom could equally go wrong with a ceiling fan/light that you may have mounted in your living room?

SaladFingers · 22 Jan 2013

Electrifying said:
Would you concede that anything that could go wrong with the extractor fan in the bathroom could equally go wrong with a ceiling fan/light that you may have mounted in your living room?

Yes, but you can switch them off.

AdamCH · 22 Jan 2013

SaladFingers said:
Electrifying said:

Would you concede that anything that could go wrong with the extractor fan in the bathroom could equally go wrong with a ceiling fan/light that you may have mounted in your living room?

Click to expand...

Yes, but you can switch them off.

What if the shaver socket on the lighting circuit goes on the fritz? Don't hear any one worrying about that. Just had a shaver socket that started humming strangly and acquired a crack in the front - never had a fan go wrong though.

SaladFingers · 22 Jan 2013

AdamCH said:
SaladFingers said:

Electrifying said:

Would you concede that anything that could go wrong with the extractor fan in the bathroom could equally go wrong with a ceiling fan/light that you may have mounted in your living room?

Click to expand...

Yes, but you can switch them off.

Click to expand...

What if the shaver socket on the lighting circuit goes on the fritz? Don't hear any one worrying about that. Just had a shaver socket that started humming strangly and acquired a crack in the front - never had a fan go wrong though.

I haven't heard anyone worry about that either, interesting point, but if one did short, then that'd be easier to disconnect.

JohnW2 · 22 Jan 2013

Electrifying said:
Would you concede that anything that could go wrong with the extractor fan in the bathroom could equally go wrong with a ceiling fan/light that you may have mounted in your living room?

Yep, at least qualitatively (the bathroom environment may make faults a bit more common) ... but would not the manufactuer's instructions for that 'fan/light' also quite probably call for an all-pole isolator?

Kind Regards, John

JohnW2 · 22 Jan 2013

AdamCH said:
What if the shaver socket on the lighting circuit goes on the fritz? Don't hear any one worrying about that. Just had a shaver socket that started humming strangly and acquired a crack in the front - never had a fan go wrong though.

Indeed - the argument can be extended to requiring separate isolators for any number of things, to the extent of becoming rather silly. What you need to understand that it is neither the Wiring Regs nor, necessarily, electricians (some certainly are no fans) who have produced this requirement for all-pole isolators for extractor fans - it is the manufacturers of the fans. We are just trying to guess their (unstated) reasons for imnposing the requirement.

Kind Regards, John

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Extractor Fan Isolator Switch????

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