10mm T&E to 6mm T&E

[farqu01]

Hi

I have recently had a bathroom replaced which had an electric shower, this was changed out for a mixer shower off the combi boiler.

The shower cable is a 10mm twin and earth which was pulled back to loft space and JB'd.
A 40amp cb fed the shower.

I am wondering if it is ok run a 6mm supply to my garage, tying into the above JB with the 10mm cable?

There will be a garage consumer unit installed which has a 40amp 30ma rcd, 32amp and 6amp cbs fitted.

The 10mm cable appears to be a horrendous,tight run hense reason asking if ok to utilise jb for supply.

Thanks

 

[Lister1987]

Hi

I have recently had a bathroom replaced which had an electric shower, this was changed out for a mixer shower off the combi boiler.

The shower cable is a 10mm twin and earth which was pulled back to loft space and JB'd.
A 40amp cb fed the shower.

I am wondering if it is ok run a 6mm supply to my garage, tying into the above JB with the 10mm cable?

There will be a garage consumer unit installed which has a 40amp 30ma rcd, 32amp and 6amp cbs fitted.

The 10mm cable appears to be a horrendous,tight run hense reason asking if ok to utilise jb for supply.

Thanks

The obvious question; What would you be looking to run with it, load wise?

 

[cliffed]

shame you can’t just continue in 10mm,but understand,no problems in changing cable to 6mm.
Mcb should be 32 amp for protection .

 

[farqu01]

The obvious question; What would you be looking to run with it, load wise?

Just lights and 3 or 4 double sockets.
Nothing pulling extensive load, need power points for general use such as hoover, karcher power washer, general every day houshold garage.
Reason I mention 6mm is that I happen to have a drum of this so if ok to use rather than purchasing 10mm cable.

Thank you

 

[ipf]

As previous, the 40 amp breaker is too big for 6mm.
Also, it would need RCD protection. It seems to be lacking, as you're intending the garage unit to have one.
Suggest you get someone qualified.

 

[telectrix]

if the 6mm is ref. method C, then a 40A breaker is OK.

 

[farqu01]

As previous, the 40 amp breaker is too big for 6mm.
Also, it would need RCD protection. It seems to be lacking, as you're intending the garage unit to have one.
Suggest you get someone qualified.

The 40 amp breaker is on the RCD side of the house consumer unit.
Going by other posts, Ill jist run in the 6mm from house CU to garage and get a 32amp breaker fitted in house cu.

 

[Dustydazzler]

In reality the chances of overloading a 6mm cable with a small garage installation is slim to none. A neat joint up in the loft via an adapter box with glands would be neat and tidy. Cable clipped above any loft insulation Would be best.
I would happily use the existing 40a for this job as long as it’s rcd protected then just put a 2 way garage consumers unit.

 

[farqu01]

shame you can’t just continue in 10mm,but understand,no problems in changing cable to 6mm.
Mcb should be 32 amp for protection .

So if I change the breaker to 32amp I could then tie the 6mm cable into the jb with the 10mm cable?
The 10mm cable breaker us on the rcd side of the house cu.

 

[GBDamo]

As previous, the 40 amp breaker is too big for 6mm.
Also, it would need RCD protection. It seems to be lacking, as you're intending the garage unit to have one.
Suggest you get someone qualified.

Not sure if I've understood you right here.

40A fine if clipped direct and why the RCD, surely the circuit now becomes a distribution not a final and RCD protection should be provide in the garage CU and the 10mm/40A should be moved to the non-RCD side.

Of course all depends on garage location, cable length, type and route.

 

[farqu01]

Not sure if I've understood you right here.

40A fine if clipped direct and why the RCD, surely the circuit now becomes a distribution not a final and RCD protection should be provide in the garage CU and the 10mm/40A should be moved to the non-RCD side.

Of course all depends on garage location, cable length, type and route.

The 10mm cable is approx 10meters to where it is then jbd. There would be an approx run of 5meters from this jb to garage where the garage cu is going.

Thanks

 

[farqu01]

The 10mm cable is approx 10meters to where it is then jbd. There would be an approx run of 5meters from this jb to garage where the garage cu is going.

Thanks

That would be where I was asking if ok to tie in 6mm to.

 

[timhoward]

It would work, it would be safe, and as far as I can see it would meet the regs as long as the 6mm cable is always clipped to a wall or ceiling.
The only issue I can see is that as you have a 30ma RCD protecting this circuit, and a typical garage CU would also have a 30ma RCD you would have no discrimination - a fault in the garage could trip either or both.
If you have a spare way on the non-RCD side of the board it would be best to move the 40amp MCB to the other side of the board and keep the RCD in the garage. (exactly as @GBDamo said above).

 

[pc1966]

Yes, with a 32A breaker you have overload protection for the 6mm covering most likely routes (i.e. thermal insulation "methods" for cables).

Unless the T&E is routed so it is always visible, or at least 50mm deep, then it should be fed from the RCD side, as it has no protection against being penetrated by a nail, etc.

The issue of RCD selectivity with the garage is more of an inconvenience, and that it might result in you losing house electrics due to an outside fault (more likely with water, etc). Feeding the T&E from a non-RCD side avoids that, but then you have the shock risk along the length of the T&E which may, or may not, be acceptable depending on how vulnerable it is to damage.

Also note that T&E is not UV rated so if outside should be run in PVC trunking/conduit/etc to protect it from sunlight damage. Though to be fair a north-facing route in Scotland won't see much of that...

 

[pc1966]

Also to add, if you can get an 32A RCBO to fit your current CU so it has independent RCD protection from the house circuits then you could feed the T&E from that and simply omit the RCD in the garage CU if you want.

Two 30mA RCD in series won't be selective on a fault, but it is not in any way dangerous, just mildly inconvenient to have to check and/or reset both after some trip. Had the feed been inaccessible by the folk using the garage then it would be a whole lot more trouble and a better planned installation worth doing (e.g. SWA cable so no feed RCD necessary).

 

[ipf]

Of course all depends on garage location, cable length, type and route.

Exactly. What are the odds in a domestic situation? Presumptuous, to say the least, to leave it at 40amp.

Think what you like but I wouldn't be installing a T+E without rcd, sub feed or not.

 

[ipf]

Also to add, if you can get an 32A RCBO to fit your current CU so it has independent RCD protection from the house circuits then you could feed the T&E from that and simply omit the RCD in the garage CU if you want.

Two 30mA RCD in series won't be selective on a fault, but it is not in any way dangerous, just mildly inconvenient to have to check and/or reset both after some trip. Had the feed been inaccessible by the folk using the garage then it would be a whole lot more trouble and a better planned installation worth doing (e.g. SWA cable so no feed RCD necessary).

Plenty good points in both posts.

I think we're getting a bit involved for a DIY job, though.

It'd be a bit more interesting to see the 10mm JB arrangement in the attic.

 

[farqu01]

Ok thanks for the replies it is appreciated.
Garage is

So just to reflect

Exactly. What are the odds in a domestic situation? Presumptuous, to say the least, to leave it at 40amp.

Think what you like but I wouldn't be installing a T+E without rcd, sub feed or not.

Ok thanks for the info guys.

So what do you rekon of this then?

Change 40amp breaker for 32amp.
Use 6mm ties into 10mm via junction box then out to garage.
Keeping 32 amp breaker rcd side in house cu?

Is that workable or will i just bite the bullet and run my new 6mm cable end to end approx 20 meters. garage is attached to house so no out side cable run?

 

[pc1966]

If it is all "indoors" as an attached garage then go with the physically easier option of the 10mm-6mm join and keep it on the RCD side with a 32A breaker.

Make sure you have a proper JB that will take 10mm though. Something like this:

60A Junction Box 3 Terminal White

A selected range of special purpose moulded and stainless steel accessories

www.cef.co.uk

 

[timhoward]

Just to comment that I wasn't thinking enough about the original 10mm length when I posted above, I'd got idea it was all ref method C for some reason which as fairly stated is highly unlikely. Sorry for confusing matters.