Garage Supply - 2 way metal consumer unit in a seperate garage

[Dunc88]

Hi,
I'm installing a 2 way metal consumer unit in a seperate garage, the earthing arrangement in the property is TNCS. I am planning to install a new 4mm2 ciruit from the main consumer unit in the house, in 4mm2 swa to a garage consumer unit (5M run of cable).
There are no extraneous-conductive parts in the garage, so can I gland this swa directly into the garage consumer unit and have an RCD main switch feeding 1x 16a & 1x6a mcb? If so, how do I prevent both RCD's tripping (garage & main consumer unit)?
Would RCBO's still trip the RCD back in the main consumer unit?
Could I turn the garage into its own TT system? I could gland the swa into an adaptable box next to the garage consumer unit, & join the earth from the 4mm core to the swa inside that box, carrying the Live & Neutral through into the garage consumer unit, from there I would take a seperate earth down to an earth spike.
Thoughts/advice please!
Cheers

 

[telectrix]

as long as the feed cable from the house CU does not require RCD protection ( i.e. SWA and/or internal feed in house not subject to 522.6.101 then MCB the feed at the house CU. I'd up the cable to 3 core 6mm on a 40A MCB ... 1. to get a bit of discrimination. 2. to allow for increase in load in the future. then tere's only 1 RCD to worry about. and exten the TNC-S to the garage.

 

[Tink]

No need for RCD in series.
Use a 40A RCBO on the non-RCD side at the house CU.

 

[westward10]

Assuming the board has non rcd ways.

 

[Tink]

Ya absolutely right – I’ll hoping to shift alone the protective devices make room

Assuming the board has non rcd ways.

Ya absolutely right – I would be hoping to shift alone the protective devices make room to insert the RCBO

 

[westward10]

Why make room for an rcbo.

 

[Midwest]

No need for RCD in series.
Use a 40A RCBO on the non-RCD side at the house CU.

That's confused my small brain

PS OP there's a handy download on the home page halfway down on the right.

 

[DPG]

No need for RCD in series.
Use a 40A RCBO on the non-RCD side at the house CU.

Hopefully this is a typo.

 

[Dunc88]

Assuming the board has non rcd ways.

Thanks for the feedback all! Unfortunately not, no space for an rcbo! Its fed via an mcb on a split load board. It also starts as 4mm twin & earth before entering a weatherproof box (where i'm glanding the swa in), so from there could I not just enter the garage consumer unit and gland the cable straight in? Then just have a main switch as the circuit from the main consumer unit is protected by the rcd?

 

[Dunc88]

as long as the feed cable from the house CU does not require RCD protection ( i.e. SWA and/or internal feed in house not subject to 522.6.101 then MCB the feed at the house CU. I'd up the cable to 3 core 6mm on a 40A MCB ... 1. to get a bit of discrimination. 2. to allow for increase in load in the future. then tere's only 1 RCD to worry about. and exten the TNC-S to the garage.

I like this idea, would mean altering the work i've already done slightly, id have to remove the small peice of 4mm twin & earth, & raise the height of the adaptable box on the external wall so i can just run the cable straight into the back of the consumer unit once its glanded in... would mean the main consumer units rcd would trip but at least theres no RCD's in series?

 

[DPG]

Why do you need an RCBO for the swa?
What do you mean by 'have a main switch'?

 

[DPG]

I like this idea, would mean altering the work i've already done slightly, id have to remove the small peice of 4mm twin & earth, & raise the height of the adaptable box on the external wall so i can just run the cable straight into the back of the consumer unit once its glanded in... would mean the main consumer units rcd would trip but at least theres no RCD's in series?

Why would the main rcd in the house trip? The rcd protection would be in the garage. I think I'm missing something here.

 

[Des 56]

Yes gland it directly into the garage unit

 

[Des 56]

He has a Rcd protected supply to the garage
He can have a isolator as the main switch in the garage
Pointless TT ing and Rdc ing the garage end if its fed from a household Rcd,it would be a ---- up which pops first

Is ---- as in coin a swear word

 

[DPG]

But as per telectrix why doesn't he feed from an mcb in the house - he's using armoured so no rcd protection needed.

Yes fully agree with not tt'ing.