Garage suply

[Gary latto]

Hi hope everyone is doing ok?
Question please,
Garage with swa supply on 32a mcb in house , can I replace dp switch on garage cu with dp rcd as don't have space for both in garage cu, and would like to take swa supply off of house cu rcd and put onto none side of rcd in house to prevent nuisance tripping in future ?? No issues with tripping at moment just a thought
Cheers gary

 

[pc1966]

Yes, you really should have RCD protection in the garage and a RCD-for-switch swap is the simplest option.

However, it is hard to get selectivity (formally known as discrimination, or coordination) between protective devices unless well planned. If you can get the garage supply off a non-RCD MCB and it is a protected cable (e.g. Steel Wire Armour) so no RCD protection of the sub-main is needed then a garage RCD will give you that aspect.

However, in the event of a high over-current fault the feed MCB will almost certainly trip along with the downstream (garage) one, and possibly also the 13A plug's fuse. Usually the best option for a garage supply is to split the meter tails and use a fused switch to feed the cable, however, that is most definitely not a DIY job, and the provision of a new/modified circuit of that style is covered by the Part P building regulations in England and Wales.

So you ought to be easily to change the garage CU to have an RCD incomer, but if doing more to the feed cable then you really ought to get a professional spark to do the job.

 

[Gary latto]

Yes, you really should have RCD protection in the garage and a RCD-for-switch swap is the simplest option.

However, it is hard to get selectivity (formally known as discrimination, or coordination) between protective devices unless well planned. If you can get the garage supply off a non-RCD MCB and it is a protected cable (e.g. Steel Wire Armour) so no RCD protection of the sub-main is needed then a garage RCD will give you that aspect.

However, in the event of a high over-current fault the feed MCB will almost certainly trip along with the downstream (garage) one, and possibly also the 13A plug's fuse. Usually the best option for a garage supply is to split the meter tails and use a fused switch to feed the cable, however, that is most definitely not a DIY job, and the provision of a new/modified circuit of that style is covered by the Part P building regulations in England and Wales.

So you ought to be easily to change the garage CU to have an RCD incomer, but if doing more to the feed cable then you really ought to get a professional spark to do the job.

Cheers for reply?
Situation is supply is currently swa buried under ground on a 32amp mcb in house on rcd side of board , and small board in garage with mcb's for socket outlets and separate mcb for lighting . And wanting to put on none rcd side in house and replace main switch to rcd main switch so going on what you said I assume makes sense to do what I was thinking to do that way all circuits will be rcd protected in garage and no nuisance tripping of rcd in house if was ever an issue in garage.
Thanks for your help cheers gary

 

[radiohead]

Bear in mind that the new RCD must be of the same manufacture and spec as the garage DB, it is no longer permitted to cobble in a different make even if it fits.

 

[Gary latto]

Bear in mind that the new RCD must be of the same manufacture and spec as the garage DB, it is no longer permitted to cobble in a different make even if it fits.

Yep understood and yes it is same make as existing board so guess what I'll be doing tomorrow well for half hour at least ? thanks again did make sense just wanted it confirmed cheers , take care mate ?

 

[pc1966]

Bear in mind that the new RCD must be of the same manufacture and spec as the garage DB, it is no longer permitted to cobble in a different make even if it fits.

Yes, forgot to mention that!

Basically the problem with CU is the bus-bar arrangements are not standard, even though the DIN mounting rail is, so if you use a device that is not recommended by the CU manufacturer it can end badly and is now a factor covered by the wiring regulations.

Now "how bad?" varies, but it is something to consider seriously.

For garage CU the whole assembly is not that expensive, but rewiring to change it is a skilled job and doing that properly means testing afterwards, and that is not in the usual DIY tool or skill range.

TL;DR check you can get matching parts first!

 

[Gary latto]

Yes, forgot to mention that!

Basically the problem with CU is the bus-bar arrangements are not standard, even though the DIN mounting rail is, so if you use a device that is not recommended by the CU manufacturer it can end badly and is now a factor covered by the wiring regulations.

Now "how bad?" varies, but it is something to consider seriously.

For garage CU the whole assembly is not that expensive, but rewiring to change it is a skilled job and doing that properly means testing afterwards, and that is not in the usual DIY tool or skill range.

TL;DR check you can get matching parts first!

Just didn't want to start changing board due to wired with conduit to out going circuits which I know not a big deal but obviously easier to just replace main switch for rcd etc,
Yes I'll be testing ie ramp test for rcd and zdb etc, thanks guys appreciated ?