RCBO Or No RCBO that is the question

[Robinson]

Hi Guys, Looked at a job today. Basement flat. CU Has a Circuit feeding a small CU in the upstairs shop
cable is a 16mm T&E on a 40 amp mcb. Rest of circuits on RCBO's.
Question is Should this cable feeding shop be RCD protected? Does this become commercial?
The Board in the shop is RCD protected.

SO its just the supply cable itself that is not. which is coming from a domestic environment.
i note though the cable comes out of board in flat straight through ceiling into shop..

any thoughts

 

[Rockingit]

There is absolutely no point in RCD protecting a lone cable, in my opinion. Also, were you too, you'd have a very expensive discrimination problem to solve as you'd need a 40A S type, and that won't be cheap.

 

[robsparky1975]

Is the cable protected by trunking,if so not needing rcbo.

 

[Marvo]

What type of cable, and how is it run?

 

[Rockingit]

Is the cable protected by trunking,if so not needing rcbo.

Even if it isn't, you don't need to RCD protect a distribution circuit with a 5s disconnection time. The FINAL circuits are protected, according to the OP, which is quite (probably) correct.

 

[Deleted member 26818]

I'm assuming that the cable is concealed in a wall, and there is no other acceptable method of additional protection.
As such (again an assumption) the OP is asking whether the exception to the requirement for RCD protection due to the installation being under the control of a skilled or instructed person is applicable.

 

[Robinson]

cable goes through ceiling (from top of FLATS CU). straight up into a TRUNKING then trunk all way to board (In Shop). Shop has very very small load. few sockets and 2 strips. And under operation of skilled person, its going to be a little store room..with a little man.

Rockit: Yes Rcd s typre $$$$$$ agreed.

Yes Final circuits are protected RCD.
This a 16mm Distribution we are talking about. On a Domestic CU 40amp breaker, feeding Commercial Stores.

 

[Amp David]

If run in trunking then sounds like no need for any additional protection.

What are the chances of the flat being under the supervision of a skilled or instructed person? In other words, if buried in the wall at<50mm the RCD needed.

 

[malcolmsanford]

Even if the cable is not buried and run in trunking if the earth system is TT you may still need to have the sub main on a RCD

 

[Amp David]

Yes, true, but just presuming its not TT. Good point though

 

[Robinson]

Its TN-C-S.