Safety of wiring to extractor fan

[KKen]

My extractor fan makes a lot of noise with very little to show for it. I was hoping to do a simple swap for a replacement fan, however when looking at the wiring, it doesn't follow best practise as shown here: //www.diynot.com/wiki/electrics:lighting:fan

Instead, a 2 pole isolator switch is run directly from the lighting circuit. The neutral and permanent (isolated) live then run to the fan over T+E (no ground required). However the switched live runs from a separate piece of T+E to a junction box at the nearest light. Only the switched live wire is used in this piece of T+E.

So we have: Lighting main -> Isolator switch (perm. live and neutral) -> Fan -> Light (switched live) -> Light switch -> Lighting main

I'm not sure if this is safe to leave as it is or if it requires me to get a sparky to fix it. Money is tight at the moment so would prefer to leave it alone if it's safe.

Doesn't appear to be a "borrowed neutral" as the neutral is disconnected from the isolator and besides, they're on the same circuit anyway?

Advise appreciated.

Cheers,

Ken.

 

[JohnW2]

...Instead, a 2 pole isolator switch is run directly from the lighting circuit. The neutral and permanent (isolated) live then run to the fan over T+E (no ground required). However the switched live runs from a separate piece of T+E to a junction box at the nearest light. Only the switched live wire is used in this piece of T+E.
...I'm not sure if this is safe to leave as it is or if it requires me to get a sparky to fix it. Money is tight at the moment so would prefer to leave it alone if it's safe.

I think one only has to apply common sense to see that this is not safe - an unsuspecting person could well imagine that operating the 'isolator switch' would actually isolate the fan, whereas it would leave the 'switched live' (which would be live if the light was switched on) still live. Safety-wise, it would probably be safer with no isolating switch at all - since no-one would then gain the 'false confidence' I've mentioned above.

If there is to be an 'isolating switch', it clearly must isolate both permanent live and switched live, otherwise it does not represent a means of 'isolation'

Kind Regards, John

 

[KKen]

...Instead, a 2 pole isolator switch is run directly from the lighting circuit. The neutral and permanent (isolated) live then run to the fan over T+E (no ground required). However the switched live runs from a separate piece of T+E to a junction box at the nearest light. Only the switched live wire is used in this piece of T+E.
...I'm not sure if this is safe to leave as it is or if it requires me to get a sparky to fix it. Money is tight at the moment so would prefer to leave it alone if it's safe.

I think one only has to apply common sense to see that this is not safe - an unsuspecting person could well imagine that operating the 'isolator switch' would actually isolate the fan, whereas it would leave the 'switched live' (which would be live if the light was switched on) still live. Safety-wise, it would probably be safer with no isolating switch at all - since no-one would then gain the 'false confidence' I've mentioned above.

If there is to be an 'isolating switch', it clearly must isolate both permanent live and switched live, otherwise it does not represent a means of 'isolation'

Kind Regards, John

Agreed however a big sticker warning of such would be cheaper than a rewire if there is no other reason

 

[JohnW2]

Agreed however a big sticker warning of such would be cheaper than a rewire if there is no other reason

Labels fade, fall off, get painted and, worst of all, may not be read, even when they should be.

The proper course is clear. If one wanted to avoid that, altough I wouldn't recommend it, I would personally be inclined to do away with the 'isolator switch' completely, replacing it with just a 'straight-through' connection (and a blank cover plate). At least it would then be apparent that the only way of 'isolating' the fan would then be to switch off the entire lighting circuit.

Kind Regards, John

 

[KKen]

Agreed however a big sticker warning of such would be cheaper than a rewire if there is no other reason

Labels fade, fall off, get painted and, worst of all, may not be read, even when they should be.

The proper course is clear. If one wanted to avoid that, altough I wouldn't recommend it, I would personally be inclined to do away with the 'isolator switch' completely, replacing it with just a 'straight-through' connection (and a blank cover plate). At least it would then be apparent that the only way of 'isolating' the fan would then be to switch off the entire lighting circuit.

Kind Regards, John

Fair point. However it's blatantly obvious that there are two wires going into the unit and something clearly a bit odd in the wiring. Any future sparky who even glances at it and assumes it's isolated will probably be well used to getting a shock!

I was more concerned with whether there were any other electrical safety issues (such as the "borrowed neutral" thing which I don't pretend to understand) which could arise from such a wiring oddity. I agree on the ideal course of action, but given the limited funds and the fact that it works, I will leave it alone if it's not causing any other issues.

Thanks,

Ian.

 

[JohnW2]

Fair point. However it's blatantly obvious that there are two wires going into the unit and something clearly a bit odd in the wiring. Any future sparky who even glances at it and assumes it's isolated will probably be well used to getting a shock!

Probably true, but little consolation to anyone (including your conscience) if he ends up dead. It's also worth noting that people other than electricians have often been known to replace fans.

I was more concerned with whether there were any other electrical safety issues (such as the "borrowed neutral" thing which I don't pretend to understand) which could arise from such a wiring oddity.

If, as sounds as if it is the case, the two cables come from the same lighting circuit, then there are no 'electrical' issues other than the (potentially major) safety one I have mentioned.

I agree on the ideal course of action, but given the limited funds and the fact that it works, I will leave it alone if it's not causing any other issues.

As I said, if you are adamant about not having it sorted out 'properly', I would personally be very inclined to replace the present 'isolator' with a straight through connection - which would only be a 5 minute job. That isolator is achieving nothing, other than introducing the potential danger we've been discussing, and almost certainly can't be said to satisfying the stated requirements of the fan manufacturer (who probably say that a 3-pole isolating switch must be fitted). In the final analysis, the decision is obviously yours.

Kind Regards, John

 

[yorkspark]

Blatently obvious or not the install is substandard and doesn't comply with bs7671 wiring regs as it has 2 points of isolation.

yet you are not concerned about that and are worried about 'borrowed neutrals' which you have not got and which you say you know nothing about anyway.

can i suggest if your not going to bring it up to standard then stop wasting our time posting

 

[RF Lighting]

Blatently obvious or not the install is substandard and doesn't comply with bs7671 wiring regs as it has 2 points of isolation.

Are you absoloutely sure about that?

 

[JohnW2]

Blatently obvious or not the install is substandard and doesn't comply with bs7671 wiring regs as it has 2 points of isolation.

Are you absoloutely sure about that?

Technically, you're obviously right to ask that question, since the CU main switch (or DP RCD) would act as a 'single point of (L&N) isolation' (or the lighting circuit's MCB/RCBO/fuse would act as a 'single point of {L only} isolation') for the fan. The regs' requirement for isolation are therefore technically met.

However, as you know as well as I do, the inherent danger in what has been described results from there being an apparent means of isolation which only partially isolates the fan (requiring isolation at a second point to achieve proper isolation). That clearly is potentially dangerous, and I would hope that we could think of some reg that such an arrangement violates, even if there is some other genuine method of 'single point isolation' available!

The other issue is the 'unpaired L' conductor in the T+E coming from a light switch. In a recent discussion, whilst we were agreed that it is not a good idea ('hum radiation' etc.), the suggestion that it is contrary to the regs was never confirmed, and I personally cannot think of anything in the regs which forbids it.

Kind Regards, John.

 

[KKen]

Blatently obvious or not the install is substandard and doesn't comply with bs7671 wiring regs as it has 2 points of isolation.

yet you are not concerned about that and are worried about 'borrowed neutrals' which you have not got and which you say you know nothing about anyway.

can i suggest if your not going to bring it up to standard then stop wasting our time posting

I believe that BS7671 came into existance in 1992, so given that the house was built in the 1970s, large portions of it probably don't meet BS7671 wiring regulations. Should I get my entire house re-wired every time the regulations change?

This is not a new installation, this is an issue I have found which I suspected was not correct hence why I posted on this forum. I will get it resolved at some point, by a registered sparky and following the relevant regulations in force at the time. However surely you can appreciate that this is likely to cost £60+ and given that the economy is STILL in the toilet, I'd rather not spend that money unless it is causing a safety hazard to my family. Again, the purpose of posting here is to ascertain the urgency of the remedial work.

Thanks for the advice, I WILL get it sorted but it may need to wait until I have another need for an electrician or do more major work on the bathroom.

Ken.

Edited to add, John's suggestion of removing the isolator is fine, but I don't want to make things worse and if I get a sparky to do so, he may as well fix it properly.

 

[JohnW2]

I believe that BS7671 came into existance in 1992, ...

That's literally true, but the IEE (latterly IET) Wiring Regulations came into existance in 1882 - we are now in the second amendment of the 17th Edition. Since 1992, the Wiring Regulations have been amalgamated with BS7671 as a single document/Standard.

...so given that the house was built in the 1970s, large portions of it probably don't meet BS7671 wiring regulations. Should I get my entire house re-wired every time the regulations change?

There is no such requirement. If any part of the installation is 'changed', the regulations/BS7671 require only that the part of the installtion in question be brought up to current standards - and one can debate whether replacing a fan constitutes such a 'change'. There is, in fact, no legal requirement to comply with BS7671. However, there is a legal obligation for all electrical work to comply with Part P of the Building Regulations - and, in practice, that requirement is virtually always fulfilled by compliance with BS7671.

However, none of this is about regulations and laws (I certainly didn't mention any, and personally don't care whether you comply with them or not). It's about the fact that, judged by whatever standards, you have a potential danger (to whoever) in your installation. What has irked some people is that you seem concerned about the possibility of a 'borrowed/ shared neutral', even though you don't understand the implications of that (which would never, in itself, be a threat to life) but seem unconcerned about something which, if it persists, carries a risk (no matter how remote) of killing someone in the future.

As I said, the decision as to what to do, and when to do it, is obviously yours. People here can but advise you and offer their opiniuons.

Kind Regards, John

 

[ban-all-sheds]

such as the "borrowed neutral" thing which I don't pretend to understand

Yet you persist in arguing against advice which you do not wish to hear.

 

[KKen]

such as the "borrowed neutral" thing which I don't pretend to understand

Yet you persist in arguing against advice which you do not wish to hear.

Apologies, it was not my intention to appear to be arguing against the excellent advice that has been supplied. I was just trying to determine the urgency of the remedial work.

I will get it resolved correctly as soon as funds allow.

Thanks again for all the help.

Ken.

 

[JohnW2]

Apologies, it was not my intention to appear to be arguing against the excellent advice that has been supplied. I was just trying to determine the urgency of the remedial work.

As I said previously, I have not (until now) been making comments in relation to regulations and laws. However, if you have any concerns about such matters, you perhaps should also be considering the urgency of replacing your noisy fan. If you buy a new one, the manufactuer's instructions will very probably say that it should be installed with a 3-pole isolation switch (and maybe also a 3A fises connection unit). Since 134.1.1 of BS7671 requires that all electrical equipment be installed in accordance with the manufacturer's instructions, if you simply replace the existing fan (retaining current wiring setup) you would be non-compliant with BS7671. Whilst the law (Part P of the Building Regs) does not require compliance with BS7671 if one can present some satisfactory alternative argument for the work/installation being safe, there is absolutely no way that you could successfully argue that what you have is safe. Simply replacing the fan would therefore probably leave you on the wrong side of the law, which may or may not concern you.

Kind Regards, John