advice please

[cagedanimal2010]

im racking my brain guys! got to move a board, will be over 3 meters from incoming so need a sub main, now the sub-main will be t+e run in loft/wall, so this needs to be covered by an 30mA rcd, now the board iv moved will be a 17th edt board so it will also have 2x 30mA rcds, now to try and limit nuisance tripping to the sub main is a time delay rcd what i need? now i cant for the life off me find in the brb, what the ruling is on discrimination.
cheers for any help guys!!
danny

 

[Guest123]

Do you have to bury the T&E sub-main in the wall??? can you not surface mount in mini trunking to avoid having to use a 30mA RCD to protect it??

Or could you run it in earthed metallic conduit in the wall???

 

[malcolmsanford]

This would come under discrimination 531.2.9 where you have RCD in series.

As it's protecting a sub main you could use a 100mA normal rcd or as you say a time delay or 'S' type

 

[Guest123]

This would come under discrimination 531.2.9 where you have RCD in series.

As it's protecting a sub main you could use a 100mA normal rcd or as you say a time delay or 'S' type

Sorry Malcolm but no he couldn't.

If one of the sections of 522.6.6 cannot be satisfied, this cable must be additionally protected by a 30mA RCD as per 522.6.7 and subsequently 415.1.1

 

[malcolmsanford]

Quite right Lenny then it would have to be a S type 30mA.

Always SWA but as you said surface would be better

 

[malcolmsanford]

Thinking on further it might even have to be a RCBO for overload protection as well

 

[Guest123]

Quite right Lenny then it would have to be a S type 30mA

Now if you can find one of those you're a better man than me, for I believe there to be no such beast! as what would be the point in having an RCD to protect you if it's operation was delayed??

 

[Amp David]

My first choice for this kind of job would be SWA but suppose it depends on the area its going to be run.
For some reason it doesn't feel right to me to do sub mains in T+E

 

[malcolmsanford]

Now if you can find one of those you're a better man than me, for I believe there to be no such beast! as what would be the point in having an RCD to protect you if it's operation was delayed??

This is where I need to go in a dark room and lie down with someone giving me a rub down with the sporting life.

As you rightly point out only 100ma have time delay, I'm determined to make him use that 100mA

In my defence as an old man when I said RCBO, another part of the brain clicked in with RCCB which in theory can have current discrimination, but is hard to achieve, so therefore time is used. So what an RCCB as to do with a RCBO is again a mystery only known to me

Now where is that boy and the sporting life

 

[Guest123]

Yes, overcurrent protection is the primary concern as it's the DNO who wont guarantee their fuse over 3M. So either an RCBO or MCB & RCD combination in this instance is required.

 

[cagedanimal2010]

cheers guys really appreciate the input, think i am going to look at the swa option, see how the costing comes out.