Coding for a Ring Final Circuit 1.5/1mm

[James18288]

Afternoon all,

A quick EICR question. I have found a Ring Final Circuit that has been run in 1.5/1mm twin and earth. It is RCD protected and OCPD is a 16a type B MCB. All testing has come back as expected for a Ring final that has been installed in 1.5/1mm and the measured Zs is well within max values. The installation actually has an EIC and has been recorded as being installed in 1.5 method C.

Im not sure on coding, could arguably be C2 as it is not able to be considered a RFC in accordance with 433.1. Could be C3 as although not an approved method it’s not dangerous and the cable is protected by the OCPD. Could even arguably be no code for the same reasons as reduced conductor size is allowed for socket outlets elsewhere.
I’m torn between a C3 and C2 citing 433.1.

If coded as a C2 and asked to complete remedial works, would you consider removing one leg of the ring and have the circuit as a 16a radial, but in my opinion this does not really change the safety of the installation and still isn’t best practice due to the cable sizing?

 

[Mark Wright]

I'm not qualified to answer just found this interesting, presumably a circuit with sockets not a lighting circuit in a Ring?

what's the current carrying capacity of 3mm cable?
because that's basically what it is?

not great is it and likely to be mistaken later and put into a 32A mcb

the only reason I can think for doing it is smaller rated MCB lower max Zs
but 1.5mm?

 

[ackbarthestar]

Well its not a standard circuit arrangement.
In its favour is that most loads these days are not 3kW heaters
Against might be that a buyers solicitor would have a field day reducing the expected sale price or demand that the property meets all the current regulations for letting purposes.
Most normal people would code it as a C3 with a note and apply condititons.
Problem now is that there are many unnormal litigious C21st warriors out there waiting to strike.

 

[Strima]

TBH I wouldn't even code it. Cable is good for 19 amps method C and OCPD is 16 amps.

 

[Pete999]

TBH I wouldn't even code it. Cable is good for 19 amps method C and OCPD is 16 amps.

Don't often disagree with you Mate, but on this I do, although the cable as you say is good for 19Amps on a 16 A breaker should be OK, what would happen if there is a lot of nuisance tripping, due to people overloading the 16 Amp OCPD and someone decided to up the OCPD to a32 Amp OCPD, sorry to be at odds with someone I admire but in this case I think you are wrong, change to a 20 A radial or 32 A RFC wired in N 2.5mm2 cable

 

[SJD]

TBH I wouldn't even code it. Cable is good for 19 amps method C and OCPD is 16 amps.

I agree, and maybe even argue it would be OK on a B20 MCB (subject to max Zs and voltage drop being OK). I like creative circuits that don't follow the expected norm!

 

[Baddegg]

Surely you can only inspect and code what’s in front of you not what someone may do to it in the future?....that leaves no ends if possibilities to everything...I agree with @Strima as the circuit is designed and installed it complies I’d note that is a bit unusual but not code it....

 

[telectrix]

it's a C3 all day long, as although there is noimmediate or percieved danger, it falls foul of 433.1.204.

 

[James18288]

Bit more info, it is a 2 bed flat. The customer has never experienced any nuisance tripping in the 5 years they have lived there. There are actually 2 RFC both installed in this way, one is the kitchen ring.

my worries are that if someone has installed a RFC in this way, can I trust that they have actually installed this with reference method C?

on the other hand, if someone upgrades the OCPD to 32a, that’s not really my issue as I am giving a report on the condition of the circuit/installation as it is? If that is how we should code, then all shower circuits with 6/10mm T&E could be coded because someone could change the unit for an over powered one.

Also, from a purely design point of view, I agree that the circuit is safe and also agree that it would probably be alright on a 20a MCB. However, 433.1 says a RFC is 2.5mm/1mm or 1.5mm MICC with 30/32a OCPD only. So surely, even if it is safe it is a C3 minimum as it doesn’t meet 7671?

if it is a creative circuit not following the norm, it should be listed as a departure on the EIC with reasoning and it obviously isn’t. Arguably it could be? But why open yourself up to the hassle for the cost difference between 100m of 2.5 vs 1.5?

 

[SJD]

it's a C3 all day long, as although there is noimmediate or percieved danger, it falls foul of 433.1.204.

I would interpret 433.1.204 to say a ring with a 30A or 32A OCPD is OK in 2.5mm2 cable or greater (or 1.5mm2 MICC), because even though the OCPD is larger than the rating of the cable, it is a ring with both legs sharing the current. So such a circuit can be deemed to meet the requirements of 433.1.1

If the cable anyway meets 433.1.1 in its own right (e.g. if it would as a radial ) then I don't believe 433.1.204 is taking away the option to actually wire it as a ring. Yes it will be non-standard, and I know some people will disagree!

 

[Strima]

Don't often disagree with you Mate, but on this I do, although the cable as you say is good for 19Amps on a 16 A breaker should be OK, what would happen if there is a lot of nuisance tripping, due to people overloading the 16 Amp OCPD and someone decided to up the OCPD to a32 Amp OCPD, sorry to be at odds with someone I admire but in this case I think you are wrong, change to a 20 A radial or 32 A RFC wired in N 2.5mm2 cable

Same could be said for a 32 amp RFC with 2.5/1.5mm cable.

 

[Baddegg]

@Pete999...@strima gets an explanation and an apology for you disagreeing I just get a big fat X......am I not worthy? ?

 

[Strima]

@Pete999...@strima gets an explanation and an apology for you disagreeing I just get a big fat X......am I not worthy? ?

You must try harder!!!

 

[Baddegg]

You must try harder!!!

I agree I’m not on your level professionally and many others on here but surely I just scrape in as a human worthy of a response.......ish? ??
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I agree I’m not on your level professionally and many others on here but surely I just scrape in as a human worthy of a response.......ish? ??

Just checked with my wife.....ignore my previous statement ?

 

[Strima]

I agree I’m not on your level professionally and many others on here but surely I just scrape in as a human worthy of a response.......ish? ??
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Just checked with my wife.....ignore my previous statement ?

I am not human, I am potato hence I get more responses.

 

[telectrix]

I am not human, I am potato hence I get more responses.

as long as yous ain't got a chip on your shoulder.

 

[Baddegg]

I am not human, I am potato hence I get more responses.

That’s uncanny cos she describes me as a vegetable.....although she wasn’t that specific ?

 

[Strima]

as long as yous ain't got a chip on your shoulder.

I am a well balanced potato, I have a chip on each shoulder.

 

[pc1966]

That’s uncanny cos she describes me as a vegetable.....although she wasn’t that specific ?

Aubergine?
I will skip the emoticon for obvious reasons
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Back to the OP, it is unusual as you say but not unsafe. My own flat was on a 20A rewirable (originally, then MCB) for the RFC but sensible enough of 2.5mm T&E and never had issues of tripping without 13A fuses blow. C3 folks?

The argument about it being modified to be unsafe by changing to 32A MCB is a bit dubious as anyone doing that ought to be covered by Part P regulations (I guess, not in my backward/forward region) and they damn well should know better!

 

[davesparks]

It doesn't conform to the 'standard circuits' in BS7671, but then neither do half of the circuits we install.
Lighting circuits, cooker supplies, sub mains and many other circuits do not have standard circuits in the book but you don't go around giving them codes.

If it complies with the requirements of the regulations for circuit design and cable sizing then there is no code to be applied.

If you found a 200A ring distribution circuit would you code it just because it isn't a 32A ring wired in 2.5?