SP RCBOs and TT Installations.

[Piratepete]

Hi Guys
On a farm I have a standard 3 phase Main Board with a standard main switch on a TN-C-S supply.
Single pole 30mA RCBOs supply some local 13 Amp sockets and lighting.

If I wish to supply a Sub-board with TT earthing in another building from this Main Board can I protect it with a Single Pole 30mA RCBO in the Main Board?
The Sub-board would have a main switch and 2 cbs for lighting and a couple of 13 Amp sockets.

I haven't been able to find the relavent clause in the Regs to clarify whether single pole is acceptable or not.

Cheers
Pete

P.S I did ask this in an earlier thread but felt the question was getting lost in confusion with others!

 

[Guest123]

There is a good thread here......

http://www.electriciansforums.net/e...forum/35643-high-integrity-csu-tt-system.html


WRT the sub-main, as this is protected by the TN-C-S earth, there would be no need for a DP RCBO as the neutral can be said to be reliably at or near earth potential.

 

[steve-the-hat]

Post deleted.

 

[Piratepete]

There is a good thread here......

http://www.electriciansforums.net/e...forum/35643-high-integrity-csu-tt-system.html

Just read it. Brill!
Pete

 

[Piratepete]

I would feed the sub board from an MCB and put a double pole RCD in the sub board.

Hi Steve
Can't do that - all farm circuits have to be RCD protected - including the cable feeding the sub-board.
Regards
Pete

 

[steve-the-hat]

My bad, I should have read your post more carefully.

 

[telectrix]

i may be incorrect her, but does the cable feeding the sub -board only need a 300mA RCD as long as it's not accessible to livestock?

 

[Guest123]

i may be incorrect her, but does the cable feeding the sub -board only need a 300mA RCD as long as it's not accessible to livestock?

Correct.

Socket outlets not exceeding 32A - 30mA

Socket outlets exceeding 32A - 100mA

All other circuits - 300mA.

 

[Knobhead]

Correct.

Socket outlets not exceeding 32A - 30mA

Socket outlets exceeding 32A - 100mA

All other circuits - 300mA.

OK I’m being a bit (a lot) sardonic here.

The higher rated socket? Higher current rating, higher leakage tolerance. Is that to make sure the cows are well and truly dead?