Do you have to protect submain if wired in SWA?

[rosewood]

Hi Guys,
Sorry title should have been 'do you have to protect a submain with an rcd if wired in SWA?'

Please excuse me if this has already been asked but i cant find a straight answer to question...

I need to change a fuseboard for a split load board (2x 30ma 63amp RCD's). off this board there will be a sub main to a garage split load board which feeds some stables and a barn etc.

The board i have to change is already got 3x32a circuits and 4x6a circuits (re-wireable fuses). If i change it to a new 17th board where the main RCD's are 63amp can i still put a 63amp mcb on this board (protecting 16mm SWA to garage buried 600mm)?

Thanks

 

[JD6400]

yep....give em 32A on a 4.0mm 3 core SWA (length of run considered of course).....that will give em a 20 A A3 circuit....and 6A for lighting.....with a bit spare...

Granted 63A is a fair lick , but the way things are going now days it is far from being unlikely .

It seems to be all the rage at the moment ( Well with the ones we are involved in at least .) for even the small lower end stable yards / couple of stables at the bottom of the garden , to have showers for the horse then they want a solarium and not forgetting rug driers and even the odd American style top loading washing machine to wash the rugs with if they have more money than sense and then some form of background heating to keep the tack from going mouldy , all this before any flood lighting and the obligatory kettle !

Don't get me wrong some still do just want just a couple of lights and socket , but these types seem rarer than the other type we tend to find now .

 

[SafetyFirst]

What happened to the pic's?? Did this thread get moved half way through or something?

 

[vjsmarwick]

Hehehe was reading the posts and about all I can think about now is the 20m run between the buildings I think instead of the run I would walk it and enjoy the view while working out how best to do the job but I have seen a meter for a caravan over half a mile away fixed to the hydro pole. I had the cu changed before the owner arrived to tell me where to isolate it talk about confused looks when he saw I was done and he had the only key to the isolator. Good luck looking forward to the pics.

 

[Quinnysparks]

I'm not 100% sure, but won't you need an earth rod at the garage if it's a PME system and being outside the equipotential zone from the main installation?

 

[malcolmsanford]

I'm not 100% sure, but won't you need an earth rod at the garage if it's a PME system and being outside the equipotential zone from the main installation?

There is nothing in either the BS 7671-2008 or the ESQCR-2002 to stop you extending the equipotential zone on a TNC-S system. This is another myth within our industry with really no sound basis.

Often if there are extraneous conductive parts in the out building, such as metallic construction or water services, it is financially better to TT the installation rather than trying to take a bond back to the MET

 

[JD6400]

There is nothing in either the BS 7671-2008 or the ESQCR-2002 to stop you extending the equipotential zone on a TNC-S system. This is another myth within our industry with really no sound basis.

Often if there are extraneous conductive parts in the out building, such as metallic construction or water services, it is financially better to TT the installation rather than trying to take a bond back to the MET

Don't forget though Malcolm that there is a stable involved in this one as well , i think ?
So unless it has required measures in place for such the op has no choice but to TT .
I know you would realise this , but others following this thread in the future might not .

 

[malcolmsanford]

Thanks DP I was just looking at the garage part

Though a TN-C system is not allowed in a Agi , or any other installation come to that, you can use a PME with the use of a metal grid in one.

But in the majority of cases I think your right TT systems are used mainly in Agi

 

[Marko10010]

Sorry to drag up an old thread but I'm in a similar situation... I have a 3p 25mm swa running underground that was installed during 17ed. It is a pme system it is protected by an mccb but does anyone know does it by 17th ed regs require rcd protection? As far as I'm aware it doesnt but I cant seem to find confirmation. Thanks in advance

 

[Wilko]

... I have a 3p 25mm swa running underground that was installed during 17ed. It is a pme system it is protected by an mccb but does anyone know does it by 17th ed regs require rcd protection? As far as I'm aware it doesnt but I cant seem to find confirmation. Thanks in advance

Hi - with its mechanical protection SWA cables can be exempted from the need for RCDs due to impacts. Perhaps confirm your cable is included in the list of BS types in Reg 522.6.204(i).

 

[Marko10010]

Hi - with its mechanical protection SWA cables can be exempted from the need for RCDs due to impacts. Perhaps confirm your cable is included in the list of BS types in Reg 522.6.204(i).

Thanks for the reply but is this a code for 18th ed?
I only need it to comply with 17th.

 

[westward10]

You won't find confirmation it doesn't need it only instances where it is required. Why do you need to know if it complied to the 17th Ed.

 

[Marko10010]

You won't find confirmation it doesn't need it only instances where it is required. Why do you need to know if it complied to the 17th Ed.

Thanks Westward

I was doing a lot of remedial works at a place 2 yrs ago after a guy failed a lot of tests on it. We finished work just before 18th edition officially started.

Basically there was a plant room outside a big house and business we replaced some of the control gear and boards as the original contractor had specced. There were half a dozen sub mains going to different buildings all SWA and underground. We fitted mccbs as that was what the previous contractor had put forward. It was a pme system so that seemed fine to me.

There was one of the 3p sub mains that went out to a mini pillar in the garden then split to go to 2 other locations. A new spark has come in now complaining that there is no rcd protection on said ccts and they have now been on the phone with me now to resolve. I'm just trying to clarify before forcing my opinion that there is no regulatory requirement for it...

Does that make sense?

 

[westward10]

If they are submains and fault protection is provided by the mccb there is no reason for rcd protection on a TN earthing system. I assume the split from the pillar just feeds distribution boards.

 

[Marko10010]

If they are submains and fault protection is provided by the mccb there is no reason for rcd protection on a TN earthing system. I assume the split from the pillar just feeds distribution boards.

Yea just feeding dist boards.
Thanks for the clarity

 

[westward10]

Best thing to do is for the other spark to confirm where in the 17th Ed it would be a requirement.