sub board

[sijaysee]

You add a new 2 way CU and its a distance away from the main CU.
Utilising a spare way on the main board with a 40A mcb.

If the main board is 30mA RCD protected then am i right in
saying that the sub wont need an RCD but just a main switch?

 

[Spark123]

Possibly, depends as to what is on the sub board as to wether or not RCD protecting the supply to is it a good idea.

 

[nozspark]

Yes, you only need to RCD protect a circuit once.

EDIT...

However you might want to think about using SWA for the sub-main and just use a MCB for protection and then have an RCD in the sub DB

 

[sijaysee]

spark i didnt understand your grammar too well.

 

[Spark123]

Put simply, if you have lights and sockets on the sub board then having it fed from the RCD side of a board upstream is not imho a good idea.
Better to have a non-RCD supply and provide the RCD protection i.e. using RCBOs in the board locally.

 

[sijaysee]

but what protects the cable from the main board to sub?

 

[RF Lighting]

Why do you think it needs RCD protection?

 

[Spark123]

What way? Re the concealled cable <50mm thing? Look to protect it using another method. Use SWA, conduit, trunking or 50mm> etc etc

 

[ricicle]

Are you competant to be carrying out this work?

 

[GaryMo]

but what protects the cable from the main board to sub?

EDIT - Already answered above. Need to refresh faster.

 

[industryspark]

You dont need rcd protection of the cable from the main board to the sub board, an mcb will suffice.

however you may require rcd protection of the cable to the submain depending on the cable route.

 

[mikeyd]

You said the board you were supplying it from was RCD protected anyway.

 

[industryspark]

too slow

dam you garymo

 

[industryspark]

maybe its split load?

 

[sijaysee]

yea it is RCD protected at the main board.
The circuits on the sub need to be as they are
sockets and cooker radial.

Then wont need to use SWA. Can bury cables in the wall.