1mm CPC on Ring mains

[gselectrical]

Evening all.

I apologise if this has been discussed before but I have not got time to search previous threads!

So, upgrading distribution boards at premises where the 30A ring main circuits have a 1mm CPC rather than 1.5mm CPC. As this is no longer allowed would it be permissable to install 20A MCB's rather than 32A?

Cheers

GS

 

[M107]

From memory so long as you are putting in mcb/rcd no problem being on a 32amp.....but as I say that is without checking.

 

[PC Electrics]

Ok on a 32A MCB or 30A 1361. 1mm cpc only fails to comply on a 30A 3036. you should make it clear on the cert though that the circuit contains 1mm cpc.

---------- Post Auto-Merged at 18:19 ---------- Previous post was made at 18:17 ----------

Check the max Zs carefully 'cos the smaller cpc increases the R1+R2.

 

[NozSpark]

+1 to PC

It's only a problem on 3036's

 

[PC Electrics]

yes indeed. It's also something that gets missed a lot on PIRs - code 2.

 

[NozSpark]

Isn't it only a code 2 with 3036's

i.e. No code with semi enclosed fuses or MCB's

 

[Sidewinder]

Noz

IIRC Semi-Enclosed are 3036?...

 

[PC Electrics]

Yes, only with 3036s.

 

[gselectrical]

Right thanks lads, appreciated.

GS

 

[NozSpark]

NozIIRC Semi-Enclosed are 3036?...

Oh bum:coat

You knew what I mean't though

 

[Phoenix]

Technically as its a non standard arrangement and not found in the OSG, you need do do the adiabatic equation to establish the required cpc size and if its met or not..... in reaility as others have said unless its a rewireable fuse (or one of the older 3871 type 4 mcbs*) you are alright

*Even 1.5 cpc can be undersized on these sometimes, depending on what the zs is, a lot of them used the thermal part to hit disconnection times which was a lot worse than a 3036.