New Consumer Unit ?correct MCB's

[PaulWales]

My mother has just received the paper work for her consumer unit replacement and resiting.

From what I know there are one or two possible problems with the work/paperwork.

She has had a duel RCD unit installed. Both the light circuits are on the same RCD - I was told by the electrician this is because "all the houses around here have a shared neutral".

My concern is that the light MCB's are both 10 amp - though the light switched I have looked at are rated at 5 or 6 amp. He told me "thats OK you'll never overload the switch".

The paperwork states that the light circuits are wired in 1.5mm2 cable. How can I check this statement?

Does it matter that the switches appear to be under-rated?

The CU has the usual RCD labels on, but nothing about using the new (Brown/Blue) and old (Red/Black) cable covers.

Anything else I should look for to ensure the work has been done properly.

Many thanks

Many thanks

 

[spark1]

1. It would have been preferable to have had the shared {borrowed ] Neutral problem rectified, and if the lighting circuits are on seperate mcb s then this is a defenite No .No. and a potential Shock risk.

2. If the lights are wired in 1,5mm then a 10A. mcb is probably o.k providing any light switches and fittings are also rated to handle a short circuit fault current of the 10 A. mcb

3. If two standadrs of wiring insulation colours are installed then a notice must be provided at the consumer unit stating this .

4. You should receive a Building Regulations Compliance Certificate from your Local Authority Building Control Department. within 28 days.

 

[rebuke]

Hmm - by "shared neutral" I assume he means borrowed neutral - an acceptable solution to that is not just to stick them on the same RCD, it should be rectified...

I can't see any reason to have used 10A MCBs, you might as well use 6A ones - the only reason I can see not to is because you end up with an excess of 10A ones.

If you can post the test results, then we can take a look and see if they seem realistic - it's not unknown for people to just make up test results etc...

 

[ericmark]

Most lights in domestic have ceiling roses that double as junction boxes so limit the lighting circuits to 5/6A.

It says:- 314.1 Every installation shall be divided into circuits, as necessary, to:
(iii) take account of danger that may arise from the failure of a single circuit such as a lighting circuit

Unless emergency lights are fitted then it would not comply.

He is in a way right as far as light switches go as bulbs should have built in fuses so each single lamp should not be able to overload.

The word is "should" and all too often the new energy saving bulbs don't have this feature and when they blow with a 10A MCB it can melt the solder on bottom of bulb glueing it into the 2A rated holder meaning the whole holder needs changing.

The regulation:- 559.6.1.6 Lighting circuits incorporating B15. B22. E14. E27 or E40 lampholders shall be protected by an overcurrent protective device of maximum rating 16A.

Makes many people think it is OK to fit 10 and 16A MCB's

However:- 559.4.1 Every luminaire shall comply with the relevant standard for manufacture and test of that luminaire and shall be selected and erected in accordance with the manufacturer's instructions.

Means if ceiling rose is 5A then MCB has to be 5A so he will need to change it.

The borrowed lives are a problem and this happens where originally there was a single lighting circuit which has latter been split and the strappers used between up-stairs and down-stairs switches on a two way lighting are twin core rather than three core.

Putting both lights on same MCB would remove the problem. But using two MCB's on the same RCD would still come under the "Borrowed Neutrals" label so not allowed.

Easy way out is an emergency lamp far cheaper and easier than any other option. But to have two 10A MCB's on a house lighting does ask the question why. You can run 23 x 60w bulbs on a 6A MCB so no normal house should ever need two 10A MCB's.

 

[flameport]

Many houses do have shared (borrowed) neutrals on the stairs/hall lights.
Rewiring would probably be the preferred solution, but would generally involve significant damage to decor.

If the borrowed neutral has to remain, the realistic option would be to connect both circuits to a single RCBO.

Two MCBs is not acceptable, as switching one of them off won't fully isolate the circuits.
One MCB on a dual RCD board isn't really good enough either, as a fault on another circuit could cause total loss of all lighting.

 

[PaulWales]

Many thanks.

First off one query, the documentation I have states the lights are wired in 1.5mm2, how do I check it is 1.5mm2 not 1mm2, and would this make a difference for how it should be fused.

From what you say, if I understand correctly, options are:-

1) Sort out the borrowed neutral, redecorate as necessary, and move one lighting circuit to the other RCD. Mum will not be fussed with the "mess".

2) Reconfigure the CU so it can take an RCBO. Not sure of the CU make/type, but the MCB's and RCD's are Legend. From looking at the internal photos, I'm not sure it can be reconfigured.

3) Move both lighting circuits onto one MCB and fit/have fitted a maintained emergency light such as http://www.tlc-direct.co.uk/Products/TPS28BOEMHF.html. Mum leaves the currrent landing light on all the time - would this light be suitable?

4) ??

Knowing mum I think option 3, should the MCB be 6 amp, or using one of the current 10 amp ones OK.

Dont have the test results with me, but should have them by this afternoon/evening and will post them then.

I have put what pics I have in the following album //www.diynot.com/network/PaulWales/albums/6094 - hope the link works!!

Again many thanks one and all

 

[ban-all-sheds]

I was told by the electrician this is because "all the houses around here have a shared neutral".

I would question the title "electrician".....

 

[ericmark]

A lamp like This does not look too bad and gets around the plunged into darkness problem. Nearly every florescent lamp can be converted to emergency type and they do have the advantage even if there is a fire and all power is cut they still work. They switch on and off like any normal lamp but will also automatically light if power is cut for about 3 hours.

However These do same thing with added advantage you can remove to light way to consumer unit. If powered from same RCD as lights it will light if RCD trips but not of course if MCB to lights trip.

As to fuse size don't know how many lights in the house but already quoted how many can be run together from 6A MCB so even with one MCB unless loads of down lighters are fitted likely not a problem.

All the switches you show are single way and unless there is two way switching the shared neutral problem is unlikely to exist.

The CU you show can't readily be converted to type using RBCO as well.

the board shown has three way split having two MCB/RBCO slots not RCD protected there may be kit for your board but not really your problem.

And I agree with BAS that the guy has behaved more like a DIY'er than electrician and I question what paperwork has been left. Anyone can and should fill in an installation certificate but only the LABC and scheme registered electricians can produce the Part P completion certificate. And work like you describe would likely lose him his registered status.

If done under LABC then they also want taking to task.