new house electrics

[Paulg31]

hello

I've recently brought a new house. Before we moved in we had an electrical inspection carried out and paid for by the sellers as it was advised by the home information report. Following the inspection it was advised that the consumer unit should be changed along with new meter tails and earthing and bonding. Again the seller paid for these.

Looking through the electrical condition report and domestic electrical installation certificate there seems to be really varying circuits. I'd have expected the same circuits both pre and post new consumer unit as no other modifications were paid for. It was different companies which carried out the work. Can anyone help me understand what they might have done? For example it's gone from two lighting circuits to one? I've attached extracts from both reports.

I was only looking as we'd like a new oven and I was wondering if we'd need a circuit running in. Currently our built in electric oven is connected with a standard 13A plug. I know lots of ovens now advise on having a dedicated circuit.

I think I'm going to have to do a bit of investigation work as to what MCB switches off what and have a look at the wiring behind some of the sockets in the kitchen. Just from looking at the labels on the new consumer unit i'd have no idea without a bit of trial and error what turns of say upstairs sockets.




Cheers,
Paul

 

[endecotp]

Yes, it would have been really useful if the descriptions said e.g. "Upstairs" or "kitchen". On the face of it it seems that they've done more than just replace the CU - which os possibly a good thing.

 

[ericmark]

I will guess that the stairs lights were two way and the interlinking cables were two core. So it would seem the EICR missed the borrowed neutral but the people doing the remedial work found it.

As to dedicated circuits bs7671:2008 says that any item using more than 2kW which is not portable should have a dedicated supply. This would include the tumble drier, washing machine, oven, immersion heater, and dish washer. In real terms we tend to only have dedicated circuits for the immersion heater mainly as it runs for quite a long time.

Unless over 3kW the oven is like the other items in that although over 2 kW it does not draw that power for long so it is not really a problem. The real problem is the tumble drier or washer/drier as they use high power for a long time.

So in real terms you have no problems.

 

[flameport]

Lights combined into one circuit.
2.1 sockets was previously the cooker, fairly likely it could be put back to use for a cooker / hob / oven if required.
2.3 socket was probably a spur directly from the old fusebox, and has been put on it's own circuit, likely this is at or very near to the consumer unit.

 

[PrenticeBoyofDerry]

Circuits
1.1 looks like a shower circuit, having 10mm cable seems this could possibly be quite new, as you tend to find the older installation on 6mm
2.1 Is a 6mm cooker circuit where socket has been installed to accommodate a plug in appliance, this could be converted back to hard-wired cooker circuit. Not sure where they get the 4.00mm CPC from?
1.5 Will more than likely have two conductors in the MCB, one that was upstairs lighting circuit and the other downstairs lighting circuit, borrowed/shared neutrals will not all the two circuits to be split across two RCDs, but there is no reason they could not still be two lighting circuit on two individual MCB on the same RCD, so you can still have two lighting circuits providing they are not split across the two RCDs.

 

[JohnW2]

1.5 Will more than likely have two conductors in the MCB, one that was upstairs lighting circuit and the other downstairs lighting circuit, borrowed/shared neutrals will not all the two circuits to be split across two RCDs, but there is no reason they could not still be two lighting circuit on two individual MCB on the same RCD, so you can still have two lighting circuits providing they are not split across the two RCDs.

Indeed but, even better, get rid of the borrowed/shared neutral/live (assuming it is present, which seems very likely) and then re-split the lighting circuits and put one on each RCD. Some people would probably feel that splitting lighting across two RCDs is necessary to comply with regs.

Kind Regards, John

 

[ericmark]

I would say the "314.1 ~ (iii) take account of danger that may arise from the failure of a single circuit such as a lighting circuit ~ " is not satisfied where the lights are not split and are on the same circuits as sockets. Either some emergency lights or a RCBO are really needed to ensure should there be a problem with something plugged in you will not be plunged into darkness.

The standard method is to have sockets and lights for any one room coming off a different RCD.

There are many ways around the problem RCBO, New triple and earth cable, RF light switches, to name a few, but all cost and the electrician needs to have done an electrical installation condition report to have worked out the costs and agreed with the owner what will be done after assessing the risk. Since the work was done by the sellers you have no idea about what was agreed between them and the electrician. He may have suggested for example returning and fitting RF light switches and redistribution of the circuits once complete.

We are only looking at paperwork so no idea about the board as to if you can fit RCBO's as well or not. But the RCD can be swapped for an isolator and four RCBO's fitted in most modern boards. But if it were my house I would only worry if either it starts tripping or if you have rooms with no natural light. And if lighting is a problem then emergency lights work even when the DNO power is lost so likely a better option. I have one at the top of my stairs as in the centre of the house and very little light from outside.

 

[JohnW2]

There are many ways around the problem RCBO, New triple and earth cable, RF light switches, to name a few.

As I said, getting rid of the interconnection between circuits (borrowed/shared neutral/live) would be the ideal, and, as you say, that could be achieved by attention to the wiring or use of wireless switches (much as I hate them!). However, if that is not done, I don't see how RCBOs would help - if you re-split the lighting circuit (with 'interconnection' still present) and had one or both on RCBOs, there would surely still be a problem (i.e. one or both of the RCDs would trip), wouldn't there?

Kind Regards, John

 

[ericmark]

I have always seen the use of RCD's as splitting the supply into circuits and 314.1 would seem to say I am right. To my mind non socket supplies are less likely to fail than socket supplies so there is always a problem combining sockets and lights. However it is down to a risk assessment and to do that one has to take into account what is in the house.

My wife likes her reading lamp and at night should the lights trip then reading lamp will still be working because sockets and lights are not on the same circuit.

 

[JohnW2]

I have always seen the use of RCD's as splitting the supply into circuits and 314.1 would seem to say I am right.

Indeed, that seems to be how most people interpret it. However my point was that so long as a shared/borrowed neutral/line exists between the original two lighting circuits, putting them on two separate RCBOs (which you appeared to be suggesting was one of the possible 'solutions) will not work any more than would putting them onto two different RCDs.

Kind Regards, John

 

[ban-all-sheds]

Some people would probably feel that splitting lighting across two RCDs is necessary to comply with regs.

I would say the "314.1 ~ (iii) take account of danger that may arise from the failure of a single circuit such as a lighting circuit ~ " is not satisfied where the lights are not split and are on the same circuits as sockets. Either some emergency lights or a RCBO are really needed to ensure should there be a problem with something plugged in you will not be plunged into darkness.

I wonder how common that thinking was 14 years ago, when 314 essentially said exactly the same thing.

 

[ericmark]

I have always seen the use of RCD's as splitting the supply into circuits and 314.1 would seem to say I am right.

Indeed, that seems to be how most people interpret it. However my point was that so long as a shared/borrowed neutral/line exists between the original two lighting circuits, putting them on two separate RCBOs (which you appeared to be suggesting was one of the possible 'solutions) will not work any more than would putting them onto two different RCDs.

Kind Regards, John

Now I can see what you mean. I was not thinking of two lighting circuits on separate RCBO's, but one lighting circuit on it's own RCBO so that any problem with other circuits will not take out the lights. As it stands both ring finals and the lights are on the same RCD which means if an appliance is damaged causing a RCD to disconnect the supply you will be plunged into darkness. So to my mind using RCBO's instead of that RCD would remove that problem.

It seems to me little or no thought was used when splitting into two RCD circuits it was just a case of ease of install. The original clearly states immersion heater removed yet on second one it seems to have returned.

 

[ericmark]

Some people would probably feel that splitting lighting across two RCDs is necessary to comply with regs.

I would say the "314.1 ~ (iii) take account of danger that may arise from the failure of a single circuit such as a lighting circuit ~ " is not satisfied where the lights are not split and are on the same circuits as sockets. Either some emergency lights or a RCBO are really needed to ensure should there be a problem with something plugged in you will not be plunged into darkness.

I wonder how common that thinking was 14 years ago, when 314 essentially said exactly the same thing.

I think this was why in 2008 the wording was changed slightly. At the time I said it rather opened up a can of worms as it seemed to imply it should have always been that way we had just been misreading the regulations. So some one could claim it had never complied with the regulations so should be corrected FOC. I still feel it is leaving it open to complaint where RCD's trip. When installed there may not be any filters leaking to earth, but latter there may be enough, so without there being a fault, the RCD trips. To call back an electrician to fix what was at the time of the installation not a problem, is maybe not fair, however it would be to the courts to decide.

 

[securespark]

On the first sheet, the cpc resistance seems high for the first ring final, oddly labelled as "Plugs".

 

[JohnW2]

Now I can see what you mean. I was not thinking of two lighting circuits on separate RCBO's, but one lighting circuit on it's own RCBO so that any problem with other circuits will not take out the lights. As it stands both ring finals and the lights are on the same RCD which means if an appliance is damaged causing a RCD to disconnect the supply you will be plunged into darkness. So to my mind using RCBO's instead of that RCD would remove that problem.

Yes, that's true. However, as I said, you seemed to be suggesting that putting each of the two original lighting circuits onto separate RCBOs would be one of the possible 'solutions' to the problem of a persisting interconnection between the circuits - which, AFAICS, is not correct.

It seems to me little or no thought was used when splitting into two RCD circuits it was just a case of ease of install.

They appear to have combined, not split, the two original lighting circuits, and, as has been said, the most obvious reason would seem to be that there was an interconnection ('borrowed neutral' etc.) which precluded putting them on different RCDs. Mind you, they presumably could have left it as two circuits, each with their own MCB on the same RCD (which would have been no less compliant with 314.1 than was combining them into a single circuit), but for some reason they didn't do that. Maybe it was done by an 'electrician' who didn't realise/understand that (s)he could do that?

Kind Regards, John