Does small rewiring job require updating consumer unit?

1001things · 26 Aug 2014

I'm going to be replacing a small flat roof and nearby thin wood panel wall, which contain a ceiling light and light switch. So that part of the wiring circuit will need to be moved and maybe ought to be replaced (it is at least 25 years old, maybe past 40 years).

Do regulations require I get the consumer unit replaced if doing this please? CU is also 40+ years old, old style of wrap your own fuse wire and wooden back.

ban-all-sheds · 26 Aug 2014

Any cables which you conceal in a wall or partition at a depth of <50mm are required to have RCD protection.

So you could either faff around and get a separate RCD added to just that lighting circuit, or you could have the CU replaced, which would be a good move anyway.

ricicle · 26 Aug 2014

Might be worth getting the existing installation inspected and tested anyway as there could be other issues. This would be especially paramount if the CU were to be replaced.

plugwash · 26 Aug 2014

ban-all-sheds said:
Any cables which you conceal in a wall or partition at a depth of <50mm are required to have RCD protection.

That is not entirely true. A more correct version is.

Any cables which you conceal in a wall or partition at a depth of <50mm and which are not protected by suitable mechanical protection or earthed metal enclosure are required to have RCD protection.

Achiving suitable mechanical protection is very difficult since what you are trying to protect against is people drilling holes in the wall and a powerful drill with a good bit (remember they now make universal bits designed to drill through almost anything) will go through most reasonable attempts at mechanical protection.

However earthed metal enclosure is certainly an option either by using a cable type that has it built-in (e.g. MICC or ali-tube) or by running the wiring in earthed steel conduit.

1001things · 26 Aug 2014

many thanks all!

even though a new cu is desirable on safety grounds i'd rather be looking at that next spring if possible, so the special cable option sounds good.

if i go with the new cu though, i've a couple of follow on questions.

1) is an rcbo cu likely to suffer trips with 1972 vintage (ie rest of the house) wiring?
2) does installing a new cu require a pir to be carried out?

I'm imagining a snowball that goes directly from having just a very short section of rewiring into needing the whole house rewiring, at least in part to comply with 2014 regulations, with all the hassle and mess that brings with it.

JohnW2 · 26 Aug 2014

plugwash said:
Achiving suitable mechanical protection is very difficult since what you are trying to protect against is people drilling holes in the wall and a powerful drill with a good bit (remember they now make universal bits designed to drill through almost anything) will go through most reasonable attempts at mechanical protection.

Do you think that the regs' requirement for "suitable mechanical protection" (if not RCD protected) requires that the protection should resist a determined attempt to drill through it - or do you think that it is adequate if the protection is such that one would become aware of the fact that one had 'hit metal' (before actually drilling all the way through it)?

Kind Regards, John

OwainDIYer · 26 Aug 2014

1001things said:
CU is also 40+ years old, old style of wrap your own fuse wire and wooden back.

That is decades overdue for replacement.

OwainDIYer · 26 Aug 2014

1001things said:
1) is an rcbo cu likely to suffer trips with 1972 vintage (ie rest of the house) wiring?
2) does installing a new cu require a pir to be carried out?

I'm imagining a snowball that goes directly from having just a very short section of rewiring into needing the whole house rewiring, at least in part to comply with 2014 regulations, with all the hassle and mess that brings with it.

1. Depends on the quality of the existing wiring. Unsatisfactory wiring should not be reconnected, but it doesn't have to be strictly compliant with latest standards to be acceptable for reconnection.

2. No, but it would be very unwise not to do an inspection before changing the CU, not least because it will make testing and certifying the new CU much much harder if there are uncorrected faults.

The most serious widespread defect likely to be found is no earth to lighting circuits. If that has been omitted they really should be recabled. Otherwise a 1970s installation if done correctly to the standards of the day and with good workmanship should be stubstantially reusable. The main issue is often later bodges to deal with the insufficient number of sockets provided originally. It is often possible to break 1 ring at a mid point, run 2 new cables back to the CU, and split the existing socket ring into two, adding new sockets as you go.

Electric shower if any will often be wired in 6mm cable for a 7.5kW unit and should be upgraded to 10mm for a 10kW unit. Immersion heater if used should ideally be moved off the socket ring onto its own circuit.

plugwash · 26 Aug 2014

JohnW2 said:
plugwash said:

Achiving suitable mechanical protection is very difficult since what you are trying to protect against is people drilling holes in the wall and a powerful drill with a good bit (remember they now make universal bits designed to drill through almost anything) will go through most reasonable attempts at mechanical protection.

Click to expand...

Do you think that the regs' requirement for "suitable mechanical protection" (if not RCD protected) requires that the protection should resist a determined attempt to drill through it - or do you think that it is adequate if the protection is such that one would become aware of the fact that one had 'hit metal' (before actually drilling all the way through it)?
n

Probablly the latter. The trouble is you son't know the characterstics of the users drill and bit and therefore it's hard to calculate how much metal you would need to reasonablly garuantee that the user noticed they had hit metal before the bit went through. I certainly wouldn't think thin metal capping would be sufficient.

The appearance of universal bits is IMO a major concern for protection against drilling. Conventional masonary bits are pretty useless for drilling anything other than masonary so your protection would just have to be thick enough to prevent the hammer action punching through but presumablly these universal bits will hit the metal and keep going.

I'm also of the opinion that unearthed metal covering electric wiring is generally a bad thing, even if that wiring is double insulated and I can't think of much other than metal that would be both sufficiently tough and sufficiently clearly "not mansonary" .

This is just my opinion though, others may differ.

JohnW2 · 26 Aug 2014

plugwash said:
Probablly the latter. The trouble is you son't know the characterstics of the users drill and bit and therefore it's hard to calculate how much metal you would need to reasonablly garuantee that the user noticed they had hit metal before the bit went through. I certainly wouldn't think thin metal capping would be sufficient. The appearance of universal bits is IMO a major concern for protection against drilling.

They obviously are a bit of a concern, but I suspect not quite as much as you are suggesting/fearing. Although it is true that some of these universal bits will carrying on drilling through metal when a masonry still would just stop drilling, I think the user would very probably be aware of the fact that they were drilling through a different material.

plugwash said:
I'm also of the opinion that unearthed metal covering electric wiring is generally a bad thing, even if that wiring is double insulated and I can't think of much other than metal that would be both sufficiently tough and sufficiently clearly "not mansonary" .

Yes, I essentially agree with all that.

Kind Regards, John

1001things · 26 Aug 2014

OwainDIYer said:
1001things said:

1) is an rcbo cu likely to suffer trips with 1972 vintage (ie rest of the house) wiring?
2) does installing a new cu require a pir to be carried out?

I'm imagining a snowball that goes directly from having just a very short section of rewiring into needing the whole house rewiring, at least in part to comply with 2014 regulations, with all the hassle and mess that brings with it.

Click to expand...

1. Depends on the quality of the existing wiring. Unsatisfactory wiring should not be reconnected, but it doesn't have to be strictly compliant with latest standards to be acceptable for reconnection.

2. No, but it would be very unwise not to do an inspection before changing the CU, not least because it will make testing and certifying the new CU much much harder if there are uncorrected faults.

The most serious widespread defect likely to be found is no earth to lighting circuits. If that has been omitted they really should be recabled. Otherwise a 1970s installation if done correctly to the standards of the day and with good workmanship should be stubstantially reusable. The main issue is often later bodges to deal with the insufficient number of sockets provided originally. It is often possible to break 1 ring at a mid point, run 2 new cables back to the CU, and split the existing socket ring into two, adding new sockets as you go.

Electric shower if any will often be wired in 6mm cable for a 7.5kW unit and should be upgraded to 10mm for a 10kW unit. Immersion heater if used should ideally be moved off the socket ring onto its own circuit.

The only possible socket alteration since installed was one single socket swapped for a double, but I'm not 100% on this. Could simply have been a replacement of a double with double. Shower isn't an issue. So, sounds good to me on the usability of the existing cabling, assuming of course it was installed properly, hasn't been chewed by a mouse at any point, and the earth to lighting circuits.

On the PIR, if a PIR concludes that any rewiring is needed does this act as a legal block on continued use as a failed GasSafe check would, or is it up to the customer to choose when to rewire?

1001things · 26 Aug 2014

Couple of follow ups.

1) Are there brands of CU that are preferred (quality, reliability etc) or to avoid?
2) What should I expect to be tested in a 2014 standard PIR? eg % of sockets, switches, all circuits or just a few?

RF Lighting · 26 Aug 2014

Hager and Schneider are the best manufacturers of CUs. I avoid wylex, Crabtree, and volex due to issues with quality. Also avoid cheap CUs with three letter names such as mcg, cgd, ced etc.

Have a chat with your electrician as to how thorough you want the report to be.

ban-all-sheds · 26 Aug 2014

RF Lighting said:
Also avoid cheap CUs with three letter names such as mcg, cgd, ced etc.

MEM?

endecotp · 26 Aug 2014

Have a look at:

http://www.electricalsafetyfirst.org.uk/mediafile/100126675/Best-Practice-Guide-1.pdf

"Replacing a consumer unit in domestic premises where lighting circuits have no protective conductor".

Or, more generally, their "best practice guide 6" about replacing consumer units.

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Does small rewiring job require updating consumer unit?

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