Dual rcd????

[wisesparky]

Hi guys.
Run a 10mm to out building for garage board, out building is connected to house and it is twin and earth, as the regs state needs to be rcd protected (less than 50mm etc) but the board i got has an rcd in it to?
So what im asking is there any implications to having 2 rcd's on 1 circuit.
Many thanks guys

 

[Guest123]

Hey.

With two 30mA RCD's in line there would be no discrimination between the two so in the event of fault there is no way of telling which would trip first.

What I would say is that as you already have 30mA RCD protecting the sub-main then you dont really need another one in the DB at the garage end to protect the sockets and lights as you already have it at the house end.

How is your sub-main cable installed is it surface all the way??
Do you have any spare unprotected ways in your house DB??

You may (depending on various factors) not have to protect the sub-main with 30mA RCD and could have it on normal 32A MCB on unprotected side.

Cheers

 

[wisesparky]

Hey.

With two 30mA RCD's in line there would be no discrimination between the two so in the event of fault there is no way of telling which would trip first.

What I would say is that as you already have 30mA RCD protecting the sub-main then you dont really need another one in the DB at the garage end to protect the sockets and lights as you already have it at the house end.

How is your sub-main cable installed is it surface all the way??
Do you have any spare unprotected ways in your house DB??

You may (depending on various factors) not have to protect the sub-main with 30mA RCD and could have it on normal 32A MCB on unprotected side.

Cheers

Thanks for getting back to me.
The cable is run below floor boards and down a wall (about 20mm in) befor going out to were i will be putting new board.
was going to put it on 40amp breaker witch is covered by rcd.
so i should just get new board with a main switch and 6 and 16 or 32 amp breaker??
Once again thanks for your time.

 

[Guest123]

Hey mate.

As the sub-main cable needs 30mA protection then a unit as you have described for the garage will be fine.

Just make sure your RCD disconnection times are within limits.

Cheers.

 

[wisesparky]

Hey mate.

As the sub-main cable needs 30mA protection then a unit as you have described for the garage will be fine.

Just make sure your RCD disconnection times are within limits.

Cheers.

Thank you very much.