Garage Board - achieving discrimination?

[westward10]

Nothing stopping you going- meter-isolator-henley block

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.

 

[Deleted member 9648]

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.

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.

 

[Jay Sparks]

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

No, I was making the remark based on the OP changing the cu in the garage to a none rcd one as was suggested earlier in the thread. But tbh there would be no difference in leaving it as it is now.

Jay

 

[westward10]

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.

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.

 

[LankyWill]

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.

I was thinking the same thing with a separate cu, it would avoid nuisance tripping on the main house cu.

 

[Octopus]

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.

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.

 

[CraigL]

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?

 

[Octopus]

A better solution is a RCBO board....

 

[westward10]

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?

That would be one way or use any cable but install to a method which doesn't need additional rcd protection.

 

[CraigL]

That would be one way or use any cable but install to a method which doesn't need additional rcd protection.

Sorry I edited my post during your reply - would appreciate your feedback on my revisions pal?

 

[Flanders]

The problem you have is that 6mm twin and earth as others have said if its not more than 50mm in the wall and not protected by earthed mechanical prorection then you will nead rcd protection for it. For your situation I would say remove the main RCD in ths garage board and fit a main switch , as you say the garage will hardly be used so it is highly unlikely that the rcd in the house will be triping out. The reason i say to remove the RCD in the garage is because it will be difficult to test due to the house rcd triping and if you cant test it you can't fill out the EIC correctly

 

[westward10]

Do you mean the rcds in series, nothing dangerous about it you just don't have discrimination between rcds.

 

[Wilko]

... I'll be testing tomorrow, so if the garage rcd trips first should I change the current setup? ...

Hi - you may find that both RCDs trip during testing, showing the inconvenience of this set up. Do all the testing and hopefully all will be well. Except ... when both of the RCDs trip, which one was it that the tester recorded ?
If it tests out ok, have a think before breaking out the tools. My place is wired the same as yours and "some day" I'm going to update the house CU and I'll sort it then. But for the 5yrs I've been here it's not been a problem, just an occasional longer walk after I've plugged in something I shouldn't have.

 

[Ian1981]

The ideal scenario has been mentioned. a swa to feed the garage consumer unit with the swa on a mcb not protected by an rcd.
If your that bothered about the discrimination side of things then that's the way to go.
If that means changing your db at the origin it's your shout but if where in my own home and this was the set up I really wouldn't be that bothered.

 

[Karin]

Hi - you may find that both RCDs trip during testing, showing the inconvenience of this set up. Do all the testing and hopefully all will be well. Except ... when both of the RCDs trip, which one was it that the tester recorded ?

as an exercise, yep it's worth seeing which one is likely to go first, but for testing purposes you will only testing the downstream RCD so it's not a problem.
i'd always prefer the distribution circuit not on RCD where possible, but figure if there's an RCD on the dis. circuit at the house either way, it doesn't really matter what the incomer is at the garage for discrimination purposes?

 

[Risteard]

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

Not sure that I'd agree. It depends on the individual tripping times of the devices, so could be either (or both).

 

[Rpa07]

this threads getting longer than 'I say you say'!

 

[Deleted member 9648]

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?

Just because the garage RCD might trip first if you test, doesn't mean it will under real fault conditions. Almost certainly both will trip.
There is absolutely no point whatsoever in the garage RCD if there is already one at the source of the circuit. There's no harm either as long as the end user understands they will have two devices to reset.

 

[Rpa07]

Nail on the head @wirepuller
Under fault conditions - safety kicks in you need to investigate and rectify
Under nuisance condition - RCD (s) kick in you need to investigate and rectify (possibly then removing garage RCD)
So no harm as long as end user understands they will have to reset to devices or one whichever.
Difference with this scenario is the original tail CU to adapt box and its protection to that point - SWA after that point wouldn't need the protection.
If no fault or nuisance conditions exist, power will be supplied to garage until the cows come home.
We've all seen MUCH worse scenarios than this install.

 

[Octopus]

Not sure that I'd agree. It depends on the individual tripping times of the devices, so could be either (or both).

I was wondering if he has a MFT!