Single Pole RCBO's

Curious_Case

With the TT type of earthing, is it ok to have individual circuit protection provided by individual RCBO's (Single Pole) and no RCD's or should there be 1 or 2 upstream RCD's to provide double pole isolation if tripped.

2011

From memory there should be a main RCD for the entire installation, this would have a differential tripping current of 100 or 200mA (can't remember which). Down stream would be 30mA RCD(s).

All RCD's should be double pole.

I havn't looked at this in a long time, so it would be best to check the above in IS10101. Or maybe someone else can help you.

Are you sure it is TT? Not many of those in the ROI.

Scag Mattress

Do you mean single mod ?

Bruthal.

The upstream one for installation should have time delay. Bigger rating won't really prevent it tripping unless a fault just happens to be below its rating but above 30ma.

Curious_Case

https://www.boards.ie/discussion/comment/118360978#Comment_118360978

Thanks for replying.

Definitely TT, only Mains Phase & Mains Neutral coming on to the property, all earthing to rod.

When you say all RCD's should be double pole are you including RCBO's as a sub-category of RCD?

Curious_Case

https://www.boards.ie/discussion/comment/118361008#Comment_118361008

They are single module but also single pole, only the live gets interrupted when tripped . . .

2011

https://www.boards.ie/discussion/comment/118361045#Comment_118361045

+1

Curious_Case

I'm beginning to wonder about the earthing system . . . . Urban Detached House with earthing rod close to back wall . . . . no earth conducter coming in to house with supply.

2 Green Sheathed Earth wires (looks like 2.5mm) going from meter (there used to be 2 meters) to consumer unit earth block - could these be an indication of a TNCS system or are they there simply to ground the meter casing?

To reassure anyone reading, I'm simply considering having my consumer unit upgraded and trying to estimate the scale of the work involved. In essence, the existing wiring is in excellent condition but earth conductor from consumer unit earth block to outside earth rod doesn't seem big enough.

2011

https://www.boards.ie/discussion/comment/118365653#Comment_118365653

Most houses in ROI are TN-C-S, especially in urban areas.

"no earth conducter coming in to house with supply"

^^^This is expected for TN-C-S. See schematic below of TN-C-S.

Why do you think it is TT ?

Curious_Case

https://www.boards.ie/discussion/comment/118368826#Comment_118368826

Many thanks for taking the time to post the graphic - you are 100% correct !!!

I peeped up under the mounting board for both meter & fusebox and earth wire is Indeed coming from fusebox, not meter.

So definitely TN-C-S

Maybe it's usual to have an earth rod too ?

Have a Great Christmas!! 🙂

2011

A TN-C-S installation should have an earth rod as well. This provides the installation with a local earth reference.

Happy Christmas!