Single or double pole RCBOs???

[Amp David]

Installed a garage CU, 2 way. As the house is TNC-S an earth rod has been installed, which is giving an Ra of 102 ohms.

The supply to the garage is protected by a MCB on the non RCD side of the CU, as installation methods don't require RCD protection.

The circuit in the garage has been protected by a 30ma type B RCBO. It is only single pole. I have today been told that it has to be of the double pole kind. Have I messed up?

 

[Guest123]

As you have derived a TT form a TN-C-S then there is a possibilty of a PD arising between the combined neutral & earth of the PME and the true earth of the TT system under earth fault conditions should the RCBO operate and disconnect only the live.

Unless you are there to switch the main DP isolator off at ther same time, thiscan't be relied upon.