Wiring bathroom extractor/light off isolator switch fed by socket circuit

TheDoug · Post by **TheDoug** » Sat Dec 18, 2021 4:03 pm

Hi,
Need to install a new bathroom extractor and light, which would usually be simple enough, but the current extractor and light are fed by an isolator switch off of the socket circuit instead of the upstairs lighting.
Is it acceptable to go ahead and replace the extractor and light using the same feed isolator from the socket circuit or does it have to be changed so its being fed off the lighting circuit with just the extractor isolated separately.

thanks

Someone-Else · Post by **Someone-Else** » Sat Dec 18, 2021 6:47 pm

TheDoug wrote: ↑Sat Dec 18, 2021 4:03 pmfed by an isolator switch off of the socket circuit

Does it have a fused connection unit?

: FCU.jpg (22.59 KiB) Viewed 2214 times

Doesn't have to be this colour or switch. (or this big)

TheDoug · Post by **TheDoug** » Sat Dec 18, 2021 7:49 pm

Someone-Else wrote: ↑Sat Dec 18, 2021 6:47 pm
TheDoug wrote: ↑Sat Dec 18, 2021 4:03 pmfed by an isolator switch off of the socket circuit
Does it have a fused connection unit?

FCU.jpg

Doesn't have to be this colour or switch. (or this big)

Yeah, that's what I meant by isolation switch, the flex goes into the loft to a junction box that then has cables going to the pull cord, light and extractor.

TheDoug · Post by **TheDoug** » Sat Dec 18, 2021 7:57 pm

Assuming that its fine to run the extractor and light from that feed, would i still need to have a 3 pole isolator switch between the JB and extractor, even though both the light and extractor can just be isolated at the fused switch from the feed?

Someone-Else · Post by **Someone-Else** » Sat Dec 18, 2021 8:58 pm

You are supposed to.
The fan has to be easy to isolate, so the 3 pole isolator is supposed to be near the fan, but if that FCU is not far away..............

Neelix · Post by **Neelix** » Sat Dec 18, 2021 9:13 pm

There is absolutely no requirements for a 3 pole isolator for the fan

aeromech3 · Post by **aeromech3** » Sun Dec 19, 2021 5:37 am

Surely a 3 pole is necessary when a permanent live is fed to the fan for the run on timer?
Granted the Op has not stated it as a timer fan.

Neelix · Post by **Neelix** » Sun Dec 19, 2021 9:23 am

aeromech3 wrote: ↑Sun Dec 19, 2021 5:37 am Surely a 3 pole is necessary when a permanent live is fed to the fan for the run on timer?
Granted the Op has not stated it as a timer fan.

There is absolutely no necessity for an isolator for an extractor fan .......

OnlyMe · Post by **OnlyMe** » Sun Dec 19, 2021 9:29 am

Neelix wrote: ↑Sat Dec 18, 2021 9:13 pm There is absolutely no requirements for a 3 pole isolator for the fan

Interesting. Now is because the fused spur provides the required isolation?

Or the minimum wattage rule? Or as I suspect not required at all.

Neelix · Post by **Neelix** » Sun Dec 19, 2021 1:38 pm

OnlyMe wrote: ↑Sun Dec 19, 2021 9:29 am
Neelix wrote: ↑Sat Dec 18, 2021 9:13 pm There is absolutely no requirements for a 3 pole isolator for the fan
Interesting. Now is because the fused spur provides the required isolation?

Or the minimum wattage rule? Or as I suspect not required at all.

In this case the fan is spurred off the socket and fused down.

Somewhere in the building regs its "suggested" that for a bathroom or ensuite without windows an isolator is advantageous, but IIRC its not mandatory

ericmark · Post by **ericmark** » Sun Dec 19, 2021 4:17 pm

Neelix wrote: ↑Sat Dec 18, 2021 9:13 pm There is absolutely no requirements for a 3 pole isolator for the fan

BS7671:2008 wrote:314.1 Every installation shall be divided into circuits, as necessary, to:
(i) avoid hazards and minimize inconvenience in the event of a fault
(ii) facilitate safe inspection, testing and maintenance (see also Section 537)
(iii) take account of danger that may arise from the failure of a single circuit such as a lighting circuit
(iv) reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor currents produced by equipment in normal operation
(v) mitigate the effects of electromagnetic interferences (EMI)
(vi) prevent the indirect energizing of a circuit intended to be isolated.

The taking in account of the danger from the failure of a lighting circuit is the reason for the isolator, so should the fan become faulty it can be taken out of service allowing the lights still to be used, the same regulation is why it is often considered two RCD's are not enough, a MCB does not normally switch the neutral, a circuit = An assembly of electrical equipment supplied from the same origin and protected against overcurrent by the same protective device(s). It does not define if this overcurrent is through the circuit or from the circuit to earth (excessive protective conductor currents) so since 2008 we have needed to take into account, it does not say must, only take into account, however the problem is showing it was taken into account once it goes wrong.

So I am sure a risk assessment can be made and in light of that an isolator is not used. But the statement "There is absolutely no requirements for a 3 pole isolator for the fan" is wrong, as is a statement you must use an isolator. But any circuit altered will need RCD protection, and in a bathroom likely needs registering with the LABC. So in real terms not a DIY job as costs too much to DIY.

SilverfoxUK · Post by **SilverfoxUK** » Tue Jan 04, 2022 4:56 pm

Hi
chances are you are proposing to wire the fan in a 1.0mm twin and earth. You need to consider how you are going to protect the cable. At the moment the ring main has 2 x 2.5mm² cables serving it and in the event of a short circuit they could withstand many hundreds of amps for the split second it takes to clear the 32A MCB. Your 1.0mm cable will not stand this current. To get around this you would need to install a switched fused spur from the ring main. Change the fuse in this spur to maybe 3A. (needs be no larger) A 3 pole isolating switch is a good idea but again not strictly necessary if you have to trash the fabric of the building to get it in. The fan will be operated by a pull cord in the bathroom ceiling. You can locally isolate the fan at your new switched fuse spur. 3 pole is obviously better but you have achieved electrical isolation and you have protected the cable. Box ticked.