What would you do?

[securespark]

Got a quote:

12 way board downstairs.

8 way up: 8 way fed via split-con from 60A submain downstairs.


Dilemma: do I fit an RCD onto the submain's tails, knowing nothing of the cable route?

C'mon, speak your mind!

 

[Lectrician]

If you are changing the kit that supplies the split con, then yes.

If you are leaving the origin as it is.........umm......

 

[1john]

You could put it as a departure. It may not comply but how would you assess the risk, perhaps the home owners would be happy to have a departure for ease of versatility on the installation? On the other hand, should it be RCD protected at source then in your everage home the home owner would need to go to the 'main CU' to reset a problem anyway.

This is where the regs make things awkward, to have a 30mA RCD up front on this board in a different location is not ideal, You can bet your bottom dollar that the cable isnt 50mm deep.

Infact to look at any job done within the "17th" that didn't have RCD protection on certain curcuits, are you supposed to take this as granted that the cables are 50mm deep or are you to do some investigating, if so, how??

 

[Taylortwocities]

If you put an RCD on the sub main tails then that will be a failure point that will affect all of the 8-way board.
I would contend that is potentially more hazardous than leaving it like it is.

Any earth fault on the 8-way board will trip the RCD on the submain - at a place that is distant to the 8-way board.

The bestest option is to swop the split con for SWA, but then we are living in the real World......

 

[ajrobb]

I've no idea, but I'd have thought you either need concentric earth protection or RCD protection on the submain cables.

 

[Taylortwocities]

Do you believe that concentric provides the level of protection required by BS7671 for cables less than 50mm from the surface?

 

[ajrobb]

I suspect that concentric earth protection (e.g. SWA) is required for cables not run on the surface, buried deep (or other fictitious mechanical protection) or protected by RCD. Obviously it needs to carry the full fault current to blow the main fuse.

 

[Adam_151]

Whats the extent of your works Simon?, going along with what lec says, if its existing and you arnt touching it, i'd seek to leave it as is

 

[SimonH2]

If you put an RCD on the sub main tails then that will be a failure point that will affect all of the 8-way board.
I would contend that is potentially more hazardous than leaving it like it is.

Any earth fault on the 8-way board will trip the RCD on the submain - at a place that is distant to the 8-way board.

The bestest option is to swop the split con for SWA, but then we are living in the real World......

Would an alternative be to fit a time-delayed RCD to the supply ? If the 8 way had RCD protection then the time delay should provide discrimination for most faults on final circuits, but is this sufficient to protect the split con* ? You could argue that it's better than not protecting it, and probably better than dropping the entire 8 way for end circuit faults.

* Before a few hours ago when I read this, I wouldn't have had a clue what that was !

 

[RF Lighting]

Personally I'd leave it without RCD and list is as a departure.

I take it changing the cable to SWA or the like is not really viable, then it's a case of lesser of two evils in my opinion.

The risk of electric shock due to the penetration of screws and nails etc is low due to the line being surrounded by earth / neutral, where as the single point of failure of an RCD supplying the submains in the event of a fault, and the hazards this can create is much more of a risk.