Garage supply using PME or earth rod.

[cairns1990]

Evening gents, just seeking a little advice. Recently bought a new place, it has mostly been rewired, its on a TN-CS system. The garage which is approx a 40m run from the house is supplied by a 2.5mm cable believe it or not, it is donkeys years old. This supplies a 2 way rcd board in the garage, the wiring in the garage is all new T&E, which supplies a few lights and socket outlet.

Going to run a new 10mm SWA 3core armoured from the board, some of which will be clipped to a fence and some burried. Going to put this on a 40amp RCBO. With regards to the earthing arrangement in the garage, would it be sufficient to use the earth from the MET, or do you think it would be better to have it off an earth rod. Just thinking distance wise, might be better off with the second option. Thanks in advance. I am a qualified electrician, just have a been out the game for a couple of years.

 

[Octopus]

I wouldn't be clipping a cable to a fence - its not a permenant structure.

And surely you know its not good practice to have 2 RCD's in series

And why 40A - are you turning it into a habitable space?

 

[Deleted member 26818]

Why would you put the SWA on an RCBO?

 

[123]

It's not ideal to have 2 MCB's in series either

 

[Deleted member 26818]

It's not ideal to have 2 MCB's in series either

Not two with the same rating definitely.

 

[telectrix]

and why 10mm if you only want 40A? surely if you're going to the expense of 10mm, bung it on a 63A.and use the PME. your 10mm cpc is adequate for bonding. fuse at supply end. then MCBs at garage.

 

[cairns1990]

A fence is a fixed structure, it's new, concrete posts, concrete gravel boards, it won't be coming down very easily or anytime soon. Not converting the garage into a room, however I am sizing up for the length of the run 40m), volt drop etc and anything to be added to the garage down the line. I am aware that you don't have to have an SWA on rcd protection, I just prefer prefer to protect the armoured running to the garage.

 

[cairns1990]

and why 10mm if you only want 40A? surely if you're going to the expense of 10mm, bung it on a 63A.and use the PME. your 10mm cpc is adequate for bonding. fuse at supply end. then MCBs at garage.

Thanks telectrix, sounds like a good solution, 63a rcbo at the supply of the swa, switch the rcd in the garage board with a main fuse.

 

[Deleted member 26818]

Thanks telectrix, sounds like a good solution, 63a rcbo at the supply of the swa, switch the rcd in the garage board with a main fuse.

So if anything in the shed causes the RCD to trip, you will have to go back to the house to reset the RCD.

 

[happysteve]

and why 10mm if you only want 40A? surely if you're going to the expense of 10mm, bung it on a 63A.and use the PME. your 10mm cpc is adequate for bonding. fuse at supply end. then MCBs at garage.

10mm volt drop = 4.4mV/A/m. At 40m run, assuming there are lights in the garage (so 3% i.e. 6.9V max) then:

max Ib = (6.9 x 1000) / (4.4 x 40) = 39.2A

(not allowing for the volt drop contribution of (R1+Rn) and Ib of the lighting circuit in the garage, though likely to be small).

 

[cairns1990]

10mm volt drop = 4.4mV/A/m. At 40m run, assuming there are lights in the garage (so 3% i.e. 6.9V max) then:

max Ib = (6.9 x 1000) / (4.4 x 40) = 39.2A

(not allowing for the volt drop contribution of (R1+Rn) and Ib of the lighting circuit in the garage, though likely to be small).

Yeah 40amp rcbo then, thought initially 40amp. Cheers for your input, you've all been really helpful

 

[telectrix]

Thanks telectrix, sounds like a good solution, 63a rcbo at the supply of the swa, switch the rcd in the garage board with a main fuse.

NO. 63A fuse at supply end. RCD protection and MCBs in garage.

 

[DJ Ovengloves]

A fence is not a permanent structure in the eyes of insurance companies.

A fence is a fixed structure, it's new, concrete posts, concrete gravel boards, it won't be coming down very easily or anytime soon. Not converting the garage into a room, however I am sizing up for the length of the run 40m), volt drop etc and anything to be added to the garage down the line. I am aware that you don't have to have an SWA on rcd protection, I just prefer prefer to protect the armoured running to the garage.

 

[happysteve]

A fence is not a permanent structure in the eyes of insurance companies.

Nor is a shed (usually). I'm wondering, when wiring up a shed, would you recommend we use skyhooks or witchcraft as a method of support for the wiring system? I've looked in OSG Appendix D, and can find no reference to either.

 

[Deleted member 26818]

Only use skyhooks for temporary lighting.

 

[happysteve]

Only use skyhooks for temporary lighting.

Well, the shed lighting will be temporary as it's a temporary structure, so good advice, skyhooks for the lighting circuit then. Witchcraft for the sockets?

 

[Cadgey123]

Thanks telectrix, sounds like a good solution, 63a rcbo at the supply of the swa, switch the rcd in the garage board with a main fuse.

I don’t even think you can get a 63amp rcbo btw

 

[123]

I don’t even think you can get a 63amp rcbo btw

Don't recall ever using or seeing one, but you can get them for sure like here.

I'd be surprised if Hager and other big manufacturers don't do them, although they would charge handsomely for them no doubt

 

[Gavin John Hyde]

I don’t even think you can get a 63amp rcbo btw

Toolstation sell a Protek 63 amp RCBO for around 25 quid.
Its a type B where as most of the 63 amp ones i have seen have been type c.

 

[DJ Ovengloves]

No, it’s not. This post is however about a permanent structure.

Although what the op proposes is a bodge no matter what.

Nor is a shed (usually). I'm wondering, when wiring up a shed, would you recommend we use skyhooks or witchcraft as a method of support for the wiring system? I've looked in OSG Appendix D, and can find no reference to either.