Garage Board - achieving discrimination?

[CraigL]

Hi all,

New to the forum so thanks in advance for your help.

I've just fitted a garage board details below:
Main Consumer Unit is Dual RCD - whoever did the re-wire had already fitted 6mm t&e direct from cu into an external jb. I've connected the t&e to swa (house end) and at the garage end the swa is fitted direct to the garage board.

The garage board is a dual board with an rcd main switch. At present I have it connected with rcds on both sides, and it is working fine. Note the garage is only used for storage and rarely used, it's not being used for a workshop. Therefore imo there is no danger caused by having rcds at either end, merely an inconvenience due to any tripping- but I don't want to leave a job if there is a 'realistic' better/safer option.

My understanding of the best option for installing a sub-main in a garage is to have the garage board rcd protected and the feed from the cu from a non-rcd protected breaker - and therefore no inconveniece tripping. However the consumer unit is dual rcd, so how is possible to fit a non-rcd protected breaker?

It's been suggested that I could have changed one block to rcbos, except the garage board breaker - but then it's an additional expense. Alternatively is it possible or even allowed to remove one of the ways from the busbar, and therefore leaving a spareway not connected to any rcd and take a direct feed from the main switch to this breaker - but this would mean 3 lives leaving the main switch, which I don't think would fit? Or could I take a feed from the live side of one of the rcds. In doing this surely I would have to fit another neutral bar and therefore I would be changing the board from it's initial design, implications??

Thinking allowed as I'm typing, even if it is possible to achieve the above scenario, doesn't this mean that the t&e from the cu to the external jb is now non-rcd protected...

Thoughts??

Thanks

 

[LankyWill]

Could Henley block the tails and install a small 2 way cu inside next to existing cu. Then supply the garage cu from the new 2 way board. This would only cost £50 tops and negate the need for rcbo's

 

[westward10]

Could Henley block the tails and install a small 2 way cu inside next to existing cu. Then supply the garage cu from the new 2 way board. This would only cost £50 tops and negate the need for rcbo's

Removing the single means of isolation.
Is the 6.0 T&E concealed in the wall it may require the rcd protection. Ditch the rcd in the garage.

 

[Jay Sparks]

Is the dual cu in the house a high integrity one? If so it should have 3 neutral bars so you can fit a new circuit from the main switch and not on any of the rcd. However, you need to make sure the 6mm twin in the house doesn't require rcd protection.

Jay

Sorry just realised you've said some of this in your OP. I shouldn't skim read!!

 

[Wilko]

Is the 6.0 T&E concealed in the wall it may require the rcd protection.

Yes, this is the question. If you change what you've got now without understanding this part you risk making an inconvenience a non compliance ...

 

[westward10]

The way I look at it is the OP has created this situation by fitting the rcd in the garage and is now looking for a solution. The correct thing to do was to fit a non rcd board in the garage as opposed to doctoring a perfectly good CU to resolve the error he has made.

 

[CraigL]

Thanks for replies

Westward - I was under the impression that rcds needed to be at the origin of the installation, and in the case of a sub-main in my case the garage board being the origin? Therefore tripping can be resolved in the garage. Obviously the original setup of the consumer unit has thrown a spanner in the works.

Wilko - Regarding the 6mm t&e I didn't install it and without ripping up the house I'd be guessing. Is my current setup compliant althought possibly an inconvenience depending which rcd trips?

Jay - 5+5 board pal.

 

[westward10]

The board in the garage is not the origin. What earthing system do you have.

 

[CraigL]

The board in the garage is not the origin. What earthing system do you have.

TN-S

 

[westward10]

The garage board does not require its own RCD protection because it has it at the point of source.

 

[Deleted member 9648]

Big time over thinking and over complication going on here. As already suggested, change the garage RCD for a main switch and the whole lot will be protected by the RCD at the house DB. There's no perfect scenario with a lot of this sort of thing, you can always find a snag whichever option is taken. Just use the simplest option in compliance with 7671 and head for the next job.

 

[LankyWill]

Removing the single means of isolation.
Is the 6.0 T&E concealed in the wall it may require the rcd protection. Ditch the rcd in the garage.

The new board would feed the garage by a 2 way rcd unit. The 6mm would still have rcd protection, you could then take the rcd protection out of the garage cu. As for the sole means of isolation the distributors fuse is still there Or you could fit a isolator.

 

[Jay Sparks]

By changing the cu in the garage to a none rcd one the only annoying thing would be if you were working in the garage and the rcd tripped, you would have to go to the house cu to turn it back on. And it would knock out all the other circuits in the house on that rcd.

Jay

 

[Wilko]

If I have understood correctly, you've got 6mm T&E from an MCB under an RCD in the house CU. Unless you can see how that cable is installed, I would assume the original installation Electrician put it under an RCD because it needed it. Having a 2nd RCD in series (in the garage) is not required but doesn't go against regs (in my opinion).

 

[westward10]

By changing the cu in the garage to a none rcd one the only annoying thing would be if you were working in the garage and the rcd tripped, you would have to go to the house cu to turn it back on. And it would knock out all the other circuits in the house on that rcd.

Jay

And by having an rcd in the garage would prevent this?

 

[CraigL]

Westward/Wirepuller - thanks for your advice. For some reason I thought in the event of tripping I needed to provide the ability to restore power to the garage, from the garage.

 

[westward10]

The new board would feed the garage by a 2 way rcd unit. The 6mm would still have rcd protection, you could then take the rcd protection out of the garage cu. As for the sole means of isolation the distributors fuse is still there Or you could fit a isolator.

Why would you lash in another CU to a perfectly good install removing the single means of isolation.

 

[LankyWill]

Why would you lash in another CU to a perfectly good install removing the single means of isolation.

Nothing stopping you going- meter-isolator-henley block

 

[Deleted member 9648]

Westward/Wirepuller - thanks for your advice. For some reason I thought in the event of tripping I needed to provide the ability to restore power to the garage, from the garage.

No requirement to do that, if that was the case any overcurrent or additional protection device at the origin of supply to an outbuilding would not comply.

 

[Pete999]

The board in the garage is not the origin. What earthing system do you have.

Westward/Wirepuller - thanks for your advice. For some reason I thought in the event of tripping I needed to provide the ability to restore power to the garage, from the garage.

2 RCDs in the same run asking for problems no discrimination whatsoever