Can anyone tell me where i can find in the regs whether or not an RCBO can be used on a TT installation.

A few threads i've seen have indicated that a TT installation requires double pole isolation. Can anyone expand?

It does indeed need double pole isolation but not necessarily double pole disconnection under fault conditions.

You need a double pole mainswitch, but you can use RCBO's on a TT installation. Personally I'd have a S type RCD mainswitch but that's because of the sort of sites I work on.


Stu

Thanks, the board does have a double pole rcd feeding it although it's not selective its just a standard MG Multi 9 100mA RCCB.

Do you know where i can find details about this in the regs.

Have a read in this previous topic:

http://www.theiet.org/forums/f...AR_FORUMVIEWTMP=Single

I've just fitted double pole rcbo's today to a TT system. The reason? Because I didn't want a neutral to earth fault to trip the rcd main switch. An S type will still detect a N-E fault and trip the entire installation. DP rcbo offers discrimination. Haven't got a regs book to hand but this is mentioned I'm sure. Or at least in a guidance note. It's certainly a good design choice.

It is indeed - 531.2.9 for one.
- Andy.

I did the same a few months ago with external CCTV on an industrial estate to avoid any unwanted tripping.

Regards

Can anyone advise on a suitable double pole RCBO for an old merlin gering metal clad board

Merlin used to make them, not sure if they still do


Stu

Hi Max,

If you don't have a time delayed main RCD then you won't get discrimination with a 30mA RCBO whether its one or 2 pole -

When theres a fault the RCBO won't limit the current, only the time before disconnection, so the main RCD may still trip.