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Electrical Test Fail in Flat - confused.

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A100man
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PostPosted: 17:24 - 23 Mar 2021    Post subject: Electrical Test Fail in Flat - confused. Reply with quote

A flat I have an interested in (part owned with ex-wife) failed an electrical test due to cooker supply incompatibity with CPC cable size. 6mm cable with 2.5mm CPC/Earth and a 30 A fuse/MCB.

Here's what he wrote..

'Coordination between conductors and overload protective devices (433.1; 533.2.1). is in
a dangerous condition and presents risk of injury. Immediate remedial action is required. Oven supply is undersized
2.5mm instead of 6mm earth cable on a 30amp fuse cut off so no fault protection'


Is this right? Do I have to installed an auxiliary earth?

BTW I'm having the CU changed to metal type with RCD .
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Nobby the Bastard
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PostPosted: 17:32 - 23 Mar 2021    Post subject: Reply with quote

It means the wire will melt before the circuit breaker will trip.
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A100man
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PostPosted: 17:40 - 23 Mar 2021    Post subject: Reply with quote

Nobby the Bastard wrote:
It means the wire will melt before the circuit breaker will trip.


BUT 2.5mm earth is standard for a 6mm T&E cable as far as I know. Most of the cookers and showers in the country must be connected using it. Or have I missed something.

I expect RCD protection will sort it - it usually does.
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Freddyfruitba...
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PostPosted: 17:48 - 23 Mar 2021    Post subject: Reply with quote

I don't think this is anything to do with the earth (or CPC, to be more accurate) as such.

A circuit for a cooker should be wired with 6.0mm twin-and-earth cable, due to the higher current requirement (6.0mm cable is rated at 40 amps). Yours is apparently wired using 2.5mm twin-and-earth, which is rated at 24 amps. So the immediate problem identified is the 30A breaker you have fitted - as Nobby says, in a fault condition the cable would melt before that breaker pops. If you changed that to a 20A one, it would be safe, but the question then remains as to how much current your oven draws (do you even have an electric oven/hob fitted?). Eg, if you just have a fitted oven with no hotplate, that should draw less than 20A and would be fine; however if you have a 6-ring electric hob then it won't....
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Last edited by Freddyfruitbat on 17:50 - 23 Mar 2021; edited 1 time in total
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Nobby the Bastard
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PostPosted: 17:49 - 23 Mar 2021    Post subject: Reply with quote

It strikes me as saying the supply wires are 2.5 rather than 6mm. Its not talking about the earth.

I think its supposed to say earthed rather than earth.
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Freddyfruitba...
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PostPosted: 17:59 - 23 Mar 2021    Post subject: Reply with quote

Nobby the Bastard wrote:
It strikes me as saying the supply wires are 2.5 rather than 6mm. Its not talking about the earth.

Agreed: for "...2.5mm instead of 6mm earth cable...", read "...2.5mm^2 twin & earth cable instead of 6mm^2 twin & earth cable" (where "mm^2" means "millimetres squared")
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Islander
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PostPosted: 18:17 - 23 Mar 2021    Post subject: Reply with quote

Yep as others have said the fault is the cross sectional area (CSA) of the conductors rather than the cpc. It appears that 2.5mm2 has been installed instead of 6mm2.

6mm2 T&E carries a 2.5mm2 CPC which is perfectly fine.
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MCN
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PostPosted: 18:30 - 23 Mar 2021    Post subject: Reply with quote

Call a local electrician for estimates.
It won't be massively expensive and he'll not tale too long to run a heavier cable.
If it's an old house then a lot of cables will be easy to pull through with the new cable tied to it.
Failing that, then plaster and any capping over the cables may need to be removed and made good after. With some re-decoration involved too.

But with electrics it far better safer than sorrier.

I'd go for the bigger cable rather than a small breaker.
Some prick may replace the breaker for a bigger one and set fire to the place in the process.

Some community responsibility is advised. Very Happy
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A100man
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PostPosted: 18:48 - 23 Mar 2021    Post subject: Reply with quote

Islander wrote:
Yep as others have said the fault is the cross sectional area (CSA) of the conductors rather than the cpc. It appears that 2.5mm2 has been installed instead of 6mm2.

6mm2 T&E carries a 2.5mm2 CPC which is perfectly fine.


Yes this is that cable used. mention of 2.5mm is confusing as that is standard ring main stuff but int his case refers to the CPC - circuit protect conductor (aka Earth).

This is why I don't understand the report!
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A100man
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PostPosted: 18:52 - 23 Mar 2021    Post subject: Reply with quote

My only thought was that modern regs might not think 30A down a 2.5mm2 earth will trip fast enough - hence an RCD protection (or bigger earth) is needed
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A100man
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PostPosted: 19:00 - 23 Mar 2021    Post subject: Reply with quote

MCN wrote:
Call a local electrician for estimates.


Ah well theres a thing. The rental agent got a quote for the works - 750 quid (plus VAT) for a 3 circuit CU swap! I got another electrician onto it but were trying to understand this part.. Is it a mistake?
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Freddyfruitba...
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PostPosted: 19:13 - 23 Mar 2021    Post subject: Reply with quote

A100man wrote:
Yes this is that cable used. mention of 2.5mm is confusing as that is standard ring main stuff but int his case refers to the CPC - circuit protect conductor (aka Earth).
This is why I don't understand the report!

You and me both. I thought the wording on the report was your bit in italics, which doesn't mention "CPC" at all?

So do you actually know what size cable is fitted on the cooker circuit?

A100man wrote:
750 quid (plus VAT) for a 3 circuit CU swap!

Salty, but he's covering his arse, as fitting a CU with RCDs to old circuits is a potential nightmare, as it's almost a given that the RCDs will instantly trip due to previously undetected earth leakage, which chummy will have to track down and fix. Or, he just doesn't want the job because he knows it will be a PITA
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drzsta
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PostPosted: 19:17 - 23 Mar 2021    Post subject: Reply with quote

Is this an electric cooker (hob & oven)? If so, the following apply;



-Is the cooker circuit wired in 2.5 or 6mm t&e? If 2.5mm then the report is justified.

And/or

-Is the cooker connected with 2.5mm from the cooker connection plate? If so report is justified.
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A100man
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PostPosted: 20:15 - 23 Mar 2021    Post subject: Reply with quote

Freddyfruitbat wrote:
A100man wrote:
Yes this is that cable used. mention of 2.5mm is confusing as that is standard ring main stuff but int his case refers to the CPC - circuit protect conductor (aka Earth).
This is why I don't understand the report!

You and me both. I thought the wording on the report was your bit in italics, which doesn't mention "CPC" at all?

So do you actually know what size cable is fitted on the cooker circuit?



I was beginning to wonder but later in the report it definitely states it's 6mm2 conductors with 2.5mm2 earth/CPC. I'll be able to check on Saturday when I go in with my electrician mate... As it goes it's only powering a basic oven (gas hob) so we'll be able to sort it.. I just wondered if I'd missed some new 'cooker must have 6mm CPC' reg.
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steve the grease
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PostPosted: 22:15 - 23 Mar 2021    Post subject: Reply with quote

Seems clear to me that a 6mm twin and earth cable is made with a2.5mm earth cable. So The bloke doesn't know what the fuck he is talking about.

https://www.voltimum.co.uk/articles/q-day-cpc-sizes-twin-earth-cable-there-1
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Islander
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PostPosted: 22:39 - 23 Mar 2021    Post subject: Reply with quote

A100man wrote:
Islander wrote:
Yep as others have said the fault is the cross sectional area (CSA) of the conductors rather than the cpc. It appears that 2.5mm2 has been installed instead of 6mm2.

6mm2 T&E carries a 2.5mm2 CPC which is perfectly fine.


Yes this is that cable used. mention of 2.5mm is confusing as that is standard ring main stuff but int his case refers to the CPC - circuit protect conductor (aka Earth).

This is why I don't understand the report!


I'd go and have a look for myself if I were you. Then if it is 6mm2 ask him wtf he's on about.
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steve the grease
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PostPosted: 15:59 - 24 Mar 2021    Post subject: Reply with quote

Islander wrote:
A100man wrote:


6mm2 T&E carries a 2.5mm2 CPC which is perfectly fine.


Yes this is that cable used. mention of 2.5mm is confusing as that is standard ring main stuff but int his case refers to the CPC - circuit protect conductor (aka Earth).

This is why I don't understand the report!


I'd go and have a look for myself if I were you. Then if it is 6mm2 ask him wtf he's on about.[/quote]

Surely the brown and Blue will be 6mm and the Earth will be 2.5mm As is specified as being standard for this size of cable.

My son in law is a spark and he says that some of the people doing these inspections have been on a training course lasting about 5 minutes , and they don't know their arse from their elblow.
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