Garage consumer unit

[mjf]

Fitting a garage consumer unit in a detached garage / workshop. The consumer unit in the house is a dual 30ma rcd consumer unit. An swa will feed from the house to the garage. My question is around RCD's, should the 30ma rcd at the house be used and just a 2 pole main switch at the garage, or use a 100ma at the house with a 30ma at the garage ?

 

[The Ghost]

I exported my PME to garage 20m odd. Works and tests fine. I have 30ma RCD at house and in the garage at the moment as I didn't have anything else to hand. O o!

 

[buzzlightyear]

I exported my PME to garage 20m odd. Works and tests fine. I have 30ma RCD at house and in the garage at the moment as I didn't have anything else to hand. O o!

any metal pipe work in side it .

 

[The Ghost]

any metal pipe work in side it

Nothing extraneous whatsoever.

 

[mjf]

Thanks for the replies, but what I am asking is about the protection feeding the garage consumer unit? The garage consumer unit has a 30ma rcd and 2 mcb's for lights and sockets. What I don't want is a 30ma rcd feeding another 30ma rcd from the house to the garage. As this is a domestic premises reg 411.3.3 requires additional protection for sockets not exceeding 32A via a 30ma rcd. And reg 411.3.4 requires that AC final ciruits with luminaries requires additional protection via 30ma rcd. As this is not an "AC final circuit" I'm asking what is normally best practice. As it will be a clean run of SWA cable between the 2 is it best to use a switch fuse from the house to the garage or a 100ma rcd and mcb. My thoughts are that an rcd would be the better option. Yes the garage can be a TT system.

 

[Taylortwocities]

Here we go again.
There in no need to have an RCD at the house end for this circuit. It’s SWA out to the shed.
Run the SWA from a non RCD way in the house CU, or (even better) from a separate switch/fuse.

There’s no point having a 100mA RCD feeding a 30mA RCD. There’s no telling which will trip if there is an earth fault of >100mA.
You can only discriminate RCDs on the basis of TIME. You would need a time-delayed (S type) RCD at the supply end.

 

[mjf]

Thanks Taylor, that makes sense.

 

[Spunkywads26]

I agree with Taylor.

As it is a distribution circuit and not a final circuit it does not require RCD protection. However as it is TN-C-S it must be TT at the garage end. I'm sure you are not to export the earth from the house.

Is the water supplied via metallic pipework?

Could you not split the tails at the house end, install a small garage unit next to house CU, use 100A main switch and suitable circuit breaker to supply garage CU which will have its own RCD?

 

[Midwest]

Why can't you export or extend TN-C-S?

 

[Wilko]

Do the water pipes in the garage need bonding?

 

[Squid]

Do the water pipes in the garage need bonding?

Not if they are plastic.

 

[Norah Nabino]

The house is TNCS, and the cable run to the garage approx 25m. Yes water at the garage. As the swa is not feeding any sockets or lights direct but is via a garage consumer unit I don't see why it requires a 30ma rcd at the house. If someone were to get a shock in the garage it would trip the rcd in the house and could be reset by someone in the house unaware why it's triped. Hence the 30ma rcd at the garage.

He is runing the swa from dual rcd cu.
So what does he do with the rcd on the side where the swa is run ftom??

 

[Norah Nabino]

Thanks for the replies, but what I am asking is about the protection feeding the garage consumer unit? The garage consumer unit has a 30ma rcd and 2 mcb's for lights and sockets. What I don't want is a 30ma rcd feeding another 30ma rcd from the house to the garage. As this is a domestic premises reg 411.3.3 requires additional protection for sockets not exceeding 32A via a 30ma rcd. And reg 411.3.4 requires that AC final ciruits with luminaries requires additional protection via 30ma rcd. As this is not an "AC final circuit" I'm asking what is normally best practice. As it will be a clean run of SWA cable between the 2 is it best to use a switch fuse from the house to the garage or a 100ma rcd and mcb. My thoughts are that an rcd would be the better option. Yes the garage can be a TT system.

What do you mean by it not an 'AC' final circuit? ?
I thought both the circuits are AC final circuits.

 

[DPG]

I think he means the garage feed is a submain, not a final circuit.

 

[Norah Nabino]

I think he means the garage feed is a submain, not a final circuit.

Yes true that but the op should know that the two cicuits in the garage are AC final circuits.