new house electrics

[JohnW2]

No - the situation I was talking about was where there are 2 MCBs, one for the upstairs lights and one for the down.

I'm confused! If that's what you were "talking about", why did you write:

No - that's not the problem - that would bite you if everything were on the same MCB.

??? As I said, if "everything were on the same MCB" there would only be one MCB to turn off, so when one was working on the circuit (with that one {and only} MCB necessarily turned off) there would be no L anywhere in any of the lighting circuit(s) that could bite, would there?

In your diagram poor Andy gets a DIY cardioversion no matter how the neutrals are arranged.

That was my point. As I said to Andy, this "borrowed neutral" terminology is really very misleading - what we mean is that L comes from one circuit and N from another - so, depending on where one is looking from, it can be called either 'borrowed neutral' or 'borrowed line'. In my (third) diagram, all of the upstairs cabling directly associated with the (upstairs) landing light appears to be associated with the 'upstairs lighting circuit', which would make many people feel that it was 'on' the upstairs circuit. Only at the other switch, on another floor, does that light get its L from the other circuit - so probably reasonably described as a 'borrowed line'.

Kind Regards, John

 

[EFLImpudence]

Have I missed something. What is the connection between the two load side lines of the MCBs?

 

[JohnW2]

Have I missed something. What is the connection between the two load side lines of the MCBs?

Damnit again - third time was clearly not lucky!! That connection obviously should not be there - this will teach me not to create diagrams in haste! Watch this space! Thanks for noticing!

Kind Regards, John

 

[JohnW2]

Fourth time lucky, hopefully - herewith corrected diagram!

Kind Regards, John

 

[ban-all-sheds]

I'm confused! If that's what you were "talking about", why did you write:

No - that's not the problem - that would bite you if everything were on the same MCB.

??? As I said, if "everything were on the same MCB" there would only be one MCB to turn off, so when one was working on the circuit (with that one {and only} MCB necessarily turned off) there would be no L anywhere in any of the lighting circuit(s) that could bite, would there?

Because your diagram showed Andy touching a conductor which was live because it's MCB had not been turned off.

That will bite if there is only 1 MCB.

 

[ban-all-sheds]

Fourth time lucky, hopefully - herewith corrected diagram!
View attachment 82539

Andy is still playing the fibrillation lottery by touching the line conductor of the downstairs circuit, which is still on.

You seem to be missing the point. Yes, I guess there is the potential for people to fiddle with the landing light thinking it is off because it is physically upstairs, and they have turned the upstairs MCB off and then failed to test for dead, but that would be so even if the landing light had been supplied with a neutral in the proper way.

Where the risk of a nasty surprise really lies is when working on the upstairs circuit, which is off, and which would successfully pass a dead test until its neutral conductor is cut or otherwise rendered non-continuous.

 

[JohnW2]

Andy is still playing the fibrillation lottery by touching the line conductor of the downstairs circuit, which is still on.

Indeed - and that was my point.

You seem to be missing the point. Yes, I guess there is the potential for people to fiddle with the landing light thinking it is off because it is physically upstairs, and they have turned the upstairs MCB off and then failed to test for dead, but that would be so even if the landing light had been supplied with a neutral in the proper way.

I'm not 'missing' that but, as I said, it would be fairly easy for people to believe that it was on the upstairs lighting circuit, not just because it was 'physically upstairs' but also because all of the 'upstairs wiring' associated with the light and its switch were part of the 'upstairs lighting circuit'. Testing for dead would obviously remove that hazard, but we (at least I) are talking about a situation in which that is not done.

Where the risk of a nasty surprise really lies is when working on the upstairs circuit, which is off, and which would successfully pass a dead test until its neutral conductor is cut or otherwise rendered non-continuous. ...

Yes, I accept that - and always have done - and also agree that that is a more pernicious risk. This side discussion (and my series of incorrect diagrams!) all started simply because Andy said that he didn't agree with me that, in some situations, a hazard could exist even if no neutral was disconnected.

Kind Regards, John

 

[AndyPRK]

It wasn't that I didn't agree.

It was just such an obvious risk that if a switch still works, there is likely to be a live conductor behind it!

 

[JohnW2]

It wasn't that I didn't agree.

Fair enough, but I don't think I can be blamed too much for believing:

... i don't agree with that. ... The neutral supply to the isolated circuit has to be disconnected.

It was just such an obvious risk that if a switch still works, there is likely to be a live conductor behind it!

Yes, it's an 'obvious risk' - but, as I've said, I think one has to accept the existence of people who do not perceive 'the obvious' and would not even check to see if the switch 'still works', let alone testing for dead! However, as I wrote to BAS, I do agree that the issue you were thinking of is a more pernicious (and 'subtle') one.

Kind Regards, John

 

[Paulg31]

Thanks guy. I'll do a bit of investigation on wha the circuits feed this weekend and let you know.

Some good points with splitting the light circuit again but I think as has been suggested it's not really a DIY job. I guess it'd be classed as adding a new circuit so notifiable work.

It makes sense having the majority of sockets on a different RCD to the lights, I'm surprised the guy putting the new consumer unit didn't do it like that. Unless the cables went quite long enough.

I'll update you on the weekend. Thanks for all your help so far!

 

[JohnW2]

Some good points with splitting the light circuit again but I think as has been suggested it's not really a DIY job. I guess it'd be classed as adding a new circuit so notifiable work.

Yes, I can't see that it would not count as 'adding a new circuit' - so, yes, probably notifiable. Mind you, since we're agreed that it's not really a DIY job, if you got a self-certifying electrician to do it, the 'notifiability' would not be of much consequence.

As has been said, a good few would regard having a single lighting circuit, particularly when on the same RCD as most of the sockets, as being non-compliant with the regulations. However, if you didn't want to address that directly, you could probably solve the problem by having a battery-operated (or battery-backed up) light or two (ideally proper 'emergency lights') in the house. That would also serve you in the event of a power cut, which no amount of re-arranging the CU could help!

It makes sense having the majority of sockets on a different RCD to the lights, I'm surprised the guy putting the new consumer unit didn't do it like that. Unless the cables went quite long enough.

Yes, I think most of us are 'surprised' by that. If the cables "weren't quite long enough", that could have been addressed.

Kind Regards, John

 

[Paulg31]

Hi all,

So tonight I've done a bit of investigating by switching the 'socket' circuits off one by one and checking with a lamp if they're still live. It seems:
-the front half of the house is on one 32A MCB
-the back of the house is on another 32A MCB
-next to the cooker there is a single socket and seperate FCU. Looking behind these the FCU goes to the cooker hood and another wire goes down. I'm guessing there could be a point behind the oven. Not that the oven is plugged into it as that's on the back of house circuit. 32 MCB.
-randomly there's one socket in the back of the lounge on it's own radial. The wiring inside looks newer too. 16A MCB

I've attached an image I did to make it clear to me. That seems to have cleared up the socket situation. Also I guess I could convert the point by the cooker back into a circuit just an oven.

Paul

 

[AndyPRK]

With your circuit layout, RCBO's should have been used (these are RCD & MCB in one unit) however they are more expensive.

Using the bits you have, I would probably put the blue sockets and lights on the same RCD.

And the green/purple sockets, on the other RCD.

The reason being that kitchen appliances are more likely to trip the RCD, and at least you would be left with your lights and most sockets working from the other RCD.

There are different opinions, but what you have now is silly.

What do you use the yellow socket for ?
Whats the red square ?

 

[AndyPRK]

Or if you wanted to spend some money, you could buy a C6 RCBO for your lights and
B32 RCBO for the blue sockets, and not use one RCD.

Everything else would be on the remaining RCD. (Kitchen sockets, cooker, old immersion)

Probably cost you £60 and you would need to be confident with playing with the CU.

OR !

Buy 1 B32 RCBO for blue sockets. (there is a used tatty one on ebay for £15)
You would need a bus bar to supply the RCBO though.

1st RCD could be used for lights only.

2nd RCD for remaining kitchen sockets.

 

[Paulg31]

Thank for the info.

I think installing RCBO's is probably a bit beyond what I'd feel confident doing but I do like the idea of swapping some of the circuits round as you suggested to the other RCD.

On my diagram the red box is the consumer unit. It's in the garage.

Also the yellow socket is just one below a window in the lounge. The wiring in it looks newer so it use have been added on in the not too distance past. Below it is a bit of flex which is cut of a below the socket. The bit of flex then passes through the wall to outside where it is also cut off flush to the wall. So I can only guess it used to feed something out there. I wonder if it was put in one its own radial as it may have caused less disruption that way. No chasing the wall needed as I guess the cable runs between the floors then down the void with the soil stack.