Rcd protecting new ring main

[davek]

Hi all,
I have been to look at a job, in a unit who require extra socket in a office. It is one of those building that has been split into small units,
The supply is 3ph. Each unit is supplied from mains with separate meters and a 3pole isolation switch with bs88 fuse 63a.
the board is a merlin gerin isobar 4c. the breaker are c60hb. my thought where rcbo but I can only get a c rated 32a which using table b6 gives me 0.58 ohms the zs at supply to board is 0.18.any thought or suggestions.
thanks
Dave

 

[Pete999]

Re: Rcd prottecting new ring main

Can you not spur off an existing socket, and install a rcd socket outlet?

 

[davek]

Re: Rcd prottecting new ring main

I did not want to use existing as some of it looks quite old and shabby, don't think customer would go with the expense of 7 rcd sockets fitted the other thought I had was fit a small rcd c/u nect to the board and put in a 40a b type.

 

[Pete999]

Re: Rcd prottecting new ring main

Your post never mentioned 7 new sockets mate,I'll think it over

 

[telectrix]

Re: Rcd prottecting new ring main

first question is what's the design current of the new circuit. if it's office, then a lot of the load may be IT... low current but high integrity earthing.

 

[davek]

Re: Rcd prottecting new ring main

Ok thanks sorry sometime you forget add these thing as was mainly thinking on the breaker there is about a 5 meter run to the office partion so cable length is a concern on r1+r2

 

[telectrix]

Re: Rcd prottecting new ring main

5m? that's nowt.

 

[davek]

Re: Rcd prottecting new ring main

as far as a I have been told just heater fan or some oil rad pc and printer just sort of wanted socket add all round for general use as far as I know

 

[Pete999]

Re: Rcd prottecting new ring main

Ok thanks sorry sometime you forget add these thing as was mainly thinking on the breaker there is about a 5 meter run to the office partion so cable length is a concern on r1+r2

I'm pedantic Dave you mean R1+R2 surely, try ebay for a MG b type rcbo Ive just had a quick butchers and there seems plenty to chose from

 

[davek]

Re: Rcd prottecting new ring main

5m? that's nowt.

was just sort of adding up 5 meters plus 7 drops averaging 4.5 mts per drop plus the 10 meter for run to room possibly 50 meters total cable for ring

 

[telectrix]

so, say yout rfc circuit is 50m end-end. that will give you a R1+R2 of approx 0.25Ω. addthat to your 0.18Ω, gives a Zs for the circuit of 0.43Ω. well within the 0.58Ω you quoted for the RCBO.

 

[davek]

hi pete
yes may have et one off net just ha a quick ring round must locals only ha c in some just sounds like it was something odd

 

[bigdavs83]

Can you get 20amp type c or b? If it's a small office you could wire a couple of radials in 4mm which will give you plenty to play with

 

[davek]

so, say yout rfc circuit is 50m end-end. that will give you a R1+R2 of approx 0.25Ω. addthat to your 0.18Ω, gives a Zs for the circuit of 0.0.43Ω. well within the 0.58Ω you quoted for the RCBO.

yes hope full, just didn't want be to near the limits, but may order a b type just found one on tlc cheaper than the c breaker I have so that may be the answer

 

[Deleted member 72666]

Can you get 20amp type c or b? If it's a small office you could wire a couple of radials in 4mm which will give you plenty to play with

They make them in various sizes, 6,10,16,20,25 32,40,50,63..... in 'b', 'c' and 'd' types.

 

[davek]

is it me or does this forum miss letters out lol

 

[Deleted member 72666]

is it me or does this forum miss letters out lol

.......Or punctuation and uppercase letters?

 

[telectrix]

i rarely use upper case letters. can't be arsed.

 

[Pete999]

Just done the calcs Tel did I agree with Tel not a aproblem

 

[Plonker 3]

The Schneider KQ range come in type B, simply buy one of these and remove the clip on attatchment and there you have a type B MCB that will fit this board.