Garage Board - achieving discrimination?

Post new thread

Currently reading:
Garage Board - achieving discrimination?

Discuss Garage Board - achieving discrimination? in the UK Electrical Forum area at ElectriciansForums.net

C

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
 
Sort by date Sort by votes
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
 
Upvote 0 Downvote
LankyWill said:
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
Click to expand...
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.
 
Upvote 0 Downvote
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!!
 
Last edited:
Upvote 0 Downvote
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.
 
Upvote 0 Downvote
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.
 
Upvote 0 Downvote
westward10 said:
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.
Click to expand...

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.
 
Upvote 0 Downvote
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
 
Upvote 0 Downvote
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).
 
Upvote 0 Downvote
Jay Sparks said:
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
Click to expand...
And by having an rcd in the garage would prevent this?
 
Upvote 0 Downvote
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.
 
Upvote 0 Downvote
LankyWill said:
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.
Click to expand...
Why would you lash in another CU to a perfectly good install removing the single means of isolation.
 
Upvote 0 Downvote
westward10 said:
The board in the garage is not the origin. What earthing system do you have.
Click to expand...
CraigL said:
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.
Click to expand...
2 RCDs in the same run asking for problems no discrimination whatsoever
 
Upvote 0 Downvote
westward10 said:
The obvious thing would be a non rcd garage board, why anyone thinks lashing in another board to be a good idea is quite frankly beyond me.
Click to expand...

That's what I'd do....but I can see that if you want to cover every eventuality then avoidance of the garage affecting any of the house circuits might seem a good idea. If there was a load of garden lighting for example on the circuit then you'd defo want to keep it away from the house RCD, but as the OP states a garage used for storage then I'd be quite happy to use the house DB RCD for any required additional protection.
 
Upvote 0 Downvote
wirepuller said:
That's what I'd do....but I can see that if you want to cover every eventuality then avoidance of the garage affecting any of the house circuits might seem a good idea. If there was a load of garden lighting for example on the circuit then you'd defo want to keep it away from the house RCD, but as the OP states a garage used for storage then I'd be quite happy to use the house DB RCD for any required additional protection.
Click to expand...
I see your point and it would have been better to fit a high integrity board with the garage on a separate rcbo, if required.
 
Upvote 0 Downvote
wirepuller said:
That's what I'd do....but I can see that if you want to cover every eventuality then avoidance of the garage affecting any of the house circuits might seem a good idea. If there was a load of garden lighting for example on the circuit then you'd defo want to keep it away from the house RCD, but as the OP states a garage used for storage then I'd be quite happy to use the house DB RCD for any required additional protection.
Click to expand...

I was thinking the same thing with a separate cu, it would avoid nuisance tripping on the main house cu.
 
Upvote 0 Downvote
CraigL said:
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.
Click to expand...

When you have 2 RCD's in series, of the same value, its normally the one in the main house that will trip first...

Connect up your MFT in the garage and test the RCD - then see which one will trip first.
 
Upvote 0 Downvote
Edited:
Thanks for the input all. The general advice seems to be swap out the rcd in the garage board for a main switch - but all this is doing is removing the two rcd's in series which means if the garage trips, we loose circuits on same side in the house - which is what I was trying to avoid by using an rcd protected garage board.

What is the benefit of removing swapping out the rcd in the garage board for a main switch. Is there anything dangerous about two rcds in series. I'll be testing tomorrow, so if the garage rcd trips first should I change the current setup?

For clarity am I correct in saying the ideal setup for a sub-main in the garage for this system would be:
High intergrity board, swa wired directly to breaker in cu, rcd protection fitted in garage board?
 
Last edited by a moderator:
Upvote 0 Downvote
CraigL said:
Thanks for the input all. The simple solution seems to be swap out the rcd in the garage board for a main switch.

However for clarity am I correct in saying the ideal setup for a sub-main in the garage for this system would be:
High intergrity board, swa wired directly to breaker in cu, rcd protection fitted in garage board?
Click to expand...
That would be one way or use any cable but install to a method which doesn't need additional rcd protection.
 
Upvote 0 Downvote
New posts

Reply to Garage Board - achieving discrimination? in the UK Electrical Forum area at ElectriciansForums.net

Similar Threads

Yellowhammer
  • Question
TT sub mains and discrimination..
Replies
8
Views
354
Yellowhammer
Yellowhammer
G
  • Question
UK RCD on bathroom ceiling?
Replies
7
Views
300
gggrrr209
G
J
  • Question
Mains cable to consumer unit top floor flat
Replies
18
Views
1K
DPG
DPG
strider6
  • Question
EVSE and RCD Questions.
Replies
8
Views
705
strider6
strider6
A
  • Question
First install of EV charger
Replies
14
Views
2K
baldelectrician
baldelectrician
Tiling Forum

OFFICIAL SPONSORS

Electrical Goods - Electrical Tools - Brand Names Electrician Courses Green Electrical Goods PCB Way Electrical Goods - Electrical Tools - Brand Names Pushfit Wire Connectors Electric Underfloor Heating Electrician Courses
These Official Forum Sponsors May Provide Discounts to Regular Forum Members - If you would like to sponsor us then CLICK HERE and post a thread with who you are, and we'll send you some stats etc

YOUR Unread Posts

UK Tiling Forum
This website was designed, optimised and is hosted by untold.media Operating under the name Untold Media since 2001.
    • Tiling Advice
    Back
    Top
    AdBlock Detected

    We get it, advertisements are annoying!

    Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website. For the best site experience please disable your AdBlocker.

    I've Disabled AdBlock