Only one lighting circuit..

[SUNRAY]

So what is the issue of having 2 light MCB's on one RCD? They both connect to the same neutral bar.

Shared neutrals need to be eliminated regardless of whether or not they work well. They can be a real hazard when working on 'isolated' lighting circuits and no amount of checking for dead makes them totally safe.

 

[JohnW2]

My interpretation of that reg is that if you can segregate circuits, then do. However many are quite many are quite militant over that reg whereas I see many single points of failure whereby all lighting could fail.

I sort-of agree with yoyr interpretation.

However, as I said, there is a wide spectrum of interpretations and, as you say, some are fairly extreme ('militant'). I personally regard it as being sufficiently vague ("minimize inconvenience", "take account of", "reduce the possibility of", "mitigate the effects of") that it leaves scope for a high degree of individual discretion.

Mind you, I would say that the reg is not clear enough in explaining what is meant by 'segregation' of circuits. The term is not defined iun BS7671 and, if one uses the BS7671 definition of a 'circuit', one could 'segregate' the installation (per everyday meaning of the word) into countless circuits, all protected by the same RCD - which presumably is not what they would want.

If the risk to occupants due to a loss of lighting is high, emergency lighting should be fitted rather than insisting the circuits should be split.

Exactly, but I would go further than that. You are perhaps thinking of particularly 'vulnerable' occupants, but most of the theoretical risks that get discussed would equally apply to non-vulnerable ones.

As I have said countless times, if they are concerned about this, they should insist on emergency lighting, since even splitting lighting into dozens of circuits, each with their own RCBO, would not stop people being 'plunged into darkness' by a power cut, or by operation of the cutout fuse (or, in some cases, operation of the fuse in a switch-fuse upstream of the CU) or some fault arising in the installation upstream of the origin of the final circuit in question.

Kind Regards, John

 

[JohnW2]

However there is a difference with 20 odd people wandering around in darkness, to 2 people at home.

Slightly, but even with just one or two people in the house, the oft-discussed risks of dropping pans of boil oil or falling off step ladders still exists.

One has to assess the risk, and it will change home to home, for example @JohnW2 has assessed the risk and decided there is a greater risk from a total power cut than from an RCD tripping ...

It's not really a question of comparing alternatives. In any house, loss of lighting can be due to either an RCD/MCB trip or a power cut - all I'm saying is that if I went just with many people's interpretation of the regs, I would be providing some protection against the former but none against the latter - and in happens that, in my case, the latter is the more common.

... my last house was the reverse, RCD trips were regular, this house only RCB (RBCO) trips have been due to water ingress and I have never lost lights.

Again, I don't think that makes any difference. Even if RCD trips are much more common than power cuts, the latter can still happen - so, if one regards 'being plunged into darkness' as representing a significant risk to life/limb, then one should take measures (i.e. emergency lighting) that will work in either situation. Otherwise one is just gambling (on the basis of power cuts being uncommon).

Kind Regards, John

 

[securespark]

I had a customer who complained her lighting MCB blew randomly.

On examination, it was discovered that there was in excess of 2.4kW of load on the single circuit.

 

[securespark]

When I got here, there was one lighting circuit on a 10A breaker carrying a maximum of 3,180W!

Now, there are 4 separate lighting circuits (up, down, extension and lounge).

The lounge is separate so that if the downstairs lights pop, there is some light still downstairs.

The current maximum load is 832W, but that includes 2 6 ft flu's in the kitchen and 4 table lamps in the lounge on a dimmer. I have not replaced these with a more energy efficient alternative yet.

The flus are Thorn HFs (140W) dating to 1990 and when they pop, I will replace them with LED. I don't expect them to pop. The 4 table lamps (240W) only get used very infrequently.

 

[securespark]

I sort-of agree with yoyr interpretation.

However, as I said, there is a wide spectrum of interpretations and, as you say, some are fairly extreme ('militant'). I personally regard it as being sufficiently vague ("minimize inconvenience", "take account of", "reduce the possibility of", "mitigate the effects of") that it leaves scope for a high degree of individual discretion.

You have to remember that the regs is a minimum standard.

You can exceed the requirements.

Which is what people like aptsys and I would do when planning circuits.

 

[ericmark]

So what is the issue of having 2 light MCB's on one RCD? They both connect to the same neutral bar.

Oh dear, hope your not an electrician? The problem with a borrowed neutral is a circuit which tests as dead can be live, clearly very bad.

I can excuse some one who in error causes a borrowed neutral, it happens one good reason for using a neon screwdriver, however clamp on ammeter is better, but one error is found there is no excuse for not correcting.

 

[JohnW2]

You have to remember that the regs is a minimum standard. You can exceed the requirements.

Indeed - and that's precisely what I do.

However, many people do not seem to think beyond 'the letter of the regs', even to 'the spirit of the regs'. Whilst they may be content that the 'letter of the regs' has been satisfied by splitting lighting into two or more circuits (with different RCD/RCBO protection, which the reg does not specify), since it satisfies ...

Every installation shall be divided into circuits, as necessary, to:
.... (iii) take account of hazards that may arise from the failure of a single circuit such as a lighting circuit

... I do not personally believe that it satisfies the spirit (or common sense) of "take account of hazards that may arise from the failure of a single circuit such as a lighting circuit" - since only emergency lighting can satisfy that.

Conversely, if one has (as my house does) adequate emergency lighting installed, I believe that the installation will be compliant with 314.1(iii) even if there is only one lighting circuit, since the "as necessary" of "divided into circuits, as necessary, to ..." becomes 'unnecessary' if that potential hazard has been addressed by the emergency lighting.

Which is what people like aptsys and I would do when planning circuits.

... and, as I've said, also me. However, as per the above, that does not mean that I feel that one always has to comply with an "as necessary" regulation when such compliance is not "necessary" - whereas some (maybe you and/or aptsys?) seem to feel that it does.

In practice/pragmatically, of course, the main reason for "complying unnecessarily" with regs is probably to reduce the risk of problems/arguments if/when someone with limited thinking ability subsequently undertakes an inspection (e.g. EICR) of the installation!

Kind Regards, John

 

[JohnW2]

So what is the issue of having 2 light MCB's on one RCD? They both connect to the same neutral bar.

Oh dear, hope your not an electrician? The problem with a borrowed neutral is a circuit which tests as dead can be live, clearly very bad.

Whilst I agree with your second sentence, why do you think that "having 2 light MCB's on one RCD" implies that there is a 'borrowed neutral'.

At least one of my CUs has (as a leftover from previous 'requirements') two lighting circuits protected by the same RCD (plus another protected by a different RCD) - are you suggesting that there's something wrong with that?

Kind Regards, John

 

[securespark]

Whatever I have done as an electrician, another electrician may disagree.

So much of the book can be open to interpretation; even when guides are published to help electricians, they can be wrong.

If you have one circuit and it goes out, unless ALL the luminaires (or at least one in each area/ room where there is more than one) are emergency ones, there will be areas without light.

So splitting into more than one circuit coupled with emergency luminaires is, I believe, the way to go.

 

[JohnW2]

Whatever I have done as an electrician, another electrician may disagree. So much of the book can be open to interpretation; even when guides are published to help electricians, they can be wrong.

Indeed - and the reg we are talking about is probably more open to varying interpretations than are most.

If you have one circuit and it goes out, unless ALL the luminaires (or at least one in each area/ room where there is more than one) are emergency ones, there will be areas without light.

That's obviously true. What I try to do in my house is (a) ensure that any crucial room/area is supplied only by one lighting circuit, and (b) have a (non-maintained) emergency light in each of those rooms/areas supplied by the lighting circuit supplying that area.

So splitting into more than one circuit coupled with emergency luminaires is, I believe, the way to go.

It's certainly 'belt and braces'. However, as I've said, although it's not something I do, or would do, having just a single lighting circuit for the whole house would seem to be OK if there is adequate emergency lighting in all important areas (as above).

The one thing about which I think we are probably agreed is that, despite what the 'letter of the regs' people seem to believe, IF one feels that loss of lighting results in hazards which need to be addressed, then complying with 314.1(ii) by splitting the lighting circuits does NOT address that potential hazard adequately - even though not required in domestic properties by the regs, one has to have some sort of emergency lighting to fully address that potential hazard.

Kind Regards, John

 

[conny]

In my current house, (which is rented), the CU was badly identified when we moved in 5 years ago. Circuits had been called one thing then at some later date, (I presume when the extension was built on), had been crossed through and something else written over the original. I decided to trace each circuit and re-label all the mcb's correctly.
I was pleased to discover that the upstairs lights were on two separate circuits and so were the sockets. So if one light circuit tripped there would still be another on the same floor working. Same with the sockets, two circuits for upstairs, however, what I didn't like was that the two circuits actually fed different sockets in one of the bedrooms. I.E. In the master bedroom there are 4 double sockets, 2 of these are fed from one circuit and the other 2 are fed from the other circuit. The danger here is that someone could isolate one of the sockets and think they had isolated all of them. Obviously this is where testing for dead after isolation has taken place proves its worth, but there will always be someone who 'assumes' rather than checks. I found the same scenario for the downstairs circuits, (2 light circuits, 2 socket circuits with a crossover in the same room), so had a chat with one of the electricians I used to work with and asked his opinion. Like me, he saw the 'advantage' of it, but also the danger of it. After a chat with the landlord he agreed to having it changed. So we now have separated dedicated circuits that do not feed the same rooms. CU is now correctly marked up with circuit locations and also drawn a plan of the house identifying the relevant rooms, as per the circuits, which is affixed to the inside of the CU cupboard door and can't be missed. As an addition I have also put one inside the wall cupboard door in the utility room for the benefit of the next tenants if we should ever move.
As my wife and stepson are disabled we also have re-chargeable torches placed strategically in each room. e.g. bedrooms have them close to the bed head so easily in reach when in bed, top and bottom of stairs in case someone is on the stairs if the lights fail and by all doors in the downstairs rooms. Cooker hood on it's own circuit so if kitchen lights fail hood will remain on.
I don't think there is much more we can do to try and be safe in the event of a power failure, (and we have quite a few with being in the countryside), other than install a changeover generator which would be going beyond reasonable.

 

[JohnW2]

As my wife and stepson are disabled we also have re-chargeable torches placed strategically in each room. e.g. bedrooms have them close to the bed head so easily in reach when in bed, top and bottom of stairs in case someone is on the stairs if the lights fail and by all doors in the downstairs rooms. Cooker hood on it's own circuit so if kitchen lights fail hood will remain on. I don't think there is much more we can do to try and be safe in the event of a power failure, (and we have quite a few with being in the countryside), other than install a changeover generator which would be going beyond reasonable.

If you're talking about standard rechargeable torches, one step better, for at least some locations, are things like eric illustrated earlier in this thread, such as (eric's pic) ...

They are generally pretty cheap, plug into a wall socket (hence keep charged) and will automatically light up (so you can find them) in the event that the power top the socket fails (for any reason). You can then simply lift the torch out of the cradle and use it as you would any other torch. In other words, these are a very simple version of 'emergency lighting' which are cheap and require no 'installation'.

Kind Regards, John

 

[securespark]

There is, of course, a train of thought that "hazards" in this context are electrical ones (ie exposed live parts), not consequential ones (like darkness resulting from an electrical outage).

 

[JohnW2]

There is, of course, a train of thought that "hazards" in this context are electrical ones (ie exposed live parts), not consequential ones (like darkness resulting from an electrical outage).

Indeed - so it would not be particularly surprising (or unreasonable) if BS7671 had decided to restrict itself solely to matters of 'electrical safety'.

However, in 314.1(iii) (and other places**) they have gone beyond that by talking about the potential consequential hazards created by loss of a lighting circuit - so they clearly don't (at least, totally) have that 'train of thought'.

[ ** "Other places' includes the oft-discussed issues of 'non-combustible' CUs and metal cable clips/restraints - which are essentially totally unrelated to anything to do with 'electrical safety'. ]

Kind Regards, John