UK When is an isolator not an isolator?

[clanky]

I need to add in another supply to a new workshop but im running out of space next to my dis board. I currently have two extra supplies (via tails to henley's) going to an outside barn and the utility part of my house. Looking at how these two supplies have been fitted (previous owner) the 'barn' supply is obviously the easiest option to copy due to size of the JB (80a RCD). But is this correct? The larger wylex box on the right also has a mechanical breaker on top of a cartridge fuse. I was always taught double isolation so to me the larger box is the right way despite taking up excess room. Or am i wrong and can i get away with the smaller box? ie remove the wylex unit and have 3 of the smaller RCD boxes? As ever TIA.

 

[oscar21]

The smaller unit probably hasn't got any over current protection, its more than likely just an 80A RCD as opposed to a RCBO (but maybe not) so the SWA cable isn't really protected. The one on the right hasn't got any RCD protection but has got overcurrent protection in the form of the fuse.

I would guess the outgoing SWA in both circuits probably doesn't need RCD protection at all (but it may do) but they both need fusing in some way.

If you are really struggling for space then you could replace everything there for a metal consumer unit with several MCB's to protect the outgoing SWA cables but they are much better on fuses, the ideal scenario is 3 of those wylex switch fuses.

*The SWA cables may need RCD protection if the incoming supply is a TT system (earth rod) or if they are supplying something critical that doesn't have RCD protection down stream.

*Fuses are better because even if the SWA is on a 50A MCB a fault on a 6A protected circuit downstream could still trip the 50A instead of/as well as the 6A where as a fuse probably wont blow as easy.

 

[westward10]

MCBs are not better than fuses you are almost certainly going to lose selectivity.
RCDs are used for fault, additional and fire protection. @oscar21 what would something critical be that needed RCD protection?

 

[littlespark]

just an observation..... no gromets in the top holes

 

[oscar21]

MCBs are not better than fuses you are almost certainly going to lose selectivity.
RCDs are used for fault, additional and fire protection. @oscar21 what would something critical be that needed RCD protection?

Thats why I said the SWA cables are better ON fuses, not THAN fuses.

By critical I mean sockets, hot tubs, things like that. If he replaces the RCD with a fuse because the SWA doesn't need it, whatever is on the end of it could be left unprotected. Safer the way it is now IMO.

 

[westward10]

Thats why I said the SWA cables are better ON fuses, not THAN fuses.

By critical I mean sockets, hot tubs, things like that. If he replaces the RCD with a fuse because the SWA doesn't need it, whatever is on the end of it could be left unprotected. Safer the way it is now IMO.

Apologies I misread your post.

 

[clanky]

The smaller unit probably hasn't got any over current protection, its more than likely just an 80A RCD as opposed to a RCBO (but maybe not) so the SWA cable isn't really protected. The one on the right hasn't got any RCD protection but has got overcurrent protection in the form of the fuse.

Thats correct. Its just a 100ma RCD on the left side.

I would guess the outgoing SWA in both circuits probably doesn't need RCD protection at all (but it may do) but they both need fusing in some way.

Both feeds go to a disboard with RCD incomers, so Im guessing you're correct (again) on them not needing RCD at this end?

*Fuses are better because even if the SWA is on a 50A MCB a fault on a 6A protected circuit downstream could still trip the 50A instead of/as well as the 6A where as a fuse probably wont blow as easy.

I'll be honest, this confused me. If the circuit is protected to 6A, it could still trip an upstream 50A mcb?

 

[clanky]

If you are really struggling for space then you could replace everything there for a metal consumer unit with several MCB's to protect the outgoing SWA cables but they are much better on fuses, the ideal scenario is 3 of those wylex switch fuses.

Thats what i suspected! Ive been looking around at different enclosures and it is possible to get slightly smaller ones but not by much! How about 3 of these, i suspect they might be a royal pain to wire up with 16mm tails but could it be a possible solution? (Earthing is TN-C-S according to the last EICR)

80A SP&N Fused Switch c/w 80A Fuse | Fusebox (FMS080)