Discuss Garage Supply - 2 way metal consumer unit in a seperate garage in the Electrical Forum area at ElectriciansForums.net

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Dunc88

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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
 
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.
 
No need for RCD in series.
Use a 40A RCBO on the non-RCD side at the house CU.
 
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?
 
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?
 
Why do you need an RCBO for the swa?
What do you mean by 'have a main switch'?
 
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.
 
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 :)
 
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.
 
Well Dunc,It seems to be going round in circles in this thread
The 64K dollar question,can you feed it from a non Rcd protected mcb or no :)

Add
How has the twin and earth feed to the adaptable box been wired
 
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.

I've got 14 ways at the main consumer unit, all of which are protected by the 2x rcds (7 & 7), so the 4mm comes from one of those mcbs, I was just hoping to avoid it tripping at the house (& knocking off other circuits) but because there is no space for an rcbo/none rcd protected mcb it looks like i'm going to have to just use a main switch & mcb's in the garage and deal with it if a fault does ever occur. To be honest i'm only having a few twin sockets & a couple of lights, just being over cautious!
 
Well Dunc,It seems to be going round in circles in this thread
The 64K dollar question,can you feed it from a non Rcd protected mcb or no :)

Add
How has the twin and earth feed to the adaptable box been wired

Tricky one isnt it!
I took a 4mm t&e from the mcb and buried it in the wall before drilling it and feeding it directly into the back of the adaptable box on the external wall...
 

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