Outbuilding earths

[riles]

Hi,
I would appreciate some advice on earth requirements for a new timber garage and separate workshop which will soon be erected. An existing two core armoured cable wired from the freshly rewired house will supply new supply boxes with 30mA RCD & 16 and 6 Amp MCB,s in each outbuilding. An underground junction box will split the supply to each building. I believe the house has an earth terminating next to the meter and this is common practice these days? The armoured cable is joined to the MCB controlled supply behind a blank in the kitchen wall and then goes straight outside and then underground. I don`t know if the armouring is earthed - or should be?? In the outbuildings, should I fit an earth spike and earth wires to the supply boxes??
Hope I`ve made things clear - ask away if I haven`t!
Many thanks in advance!!

 

[EFLImpudence]

I don`t know if the armouring is earthed - or should be??

Yes, it should be connected to earth at the house.

In the outbuildings, should I fit an earth spike and earth wires to the supply boxes??

Not necessary if there are no extraneous conductive parts in the out-buildings and the EFLI is sufficient for the OPD in the house.

If above is satisfactory you can connect the CPCs to the armour.

It would appear from the need to ask that you will not have the necessary equipment to determine these things so an electrician may be a good idea.

 

[PrenticeBoyofDerry]

What underground junction is being fitted?
and is this necessary and accessible?

 

[Spark123]

What sort of equipment will you have in this workshop?

 

[riles]

Thanks for the swift replies.
The underground box will be a Pratley 3 way size 0 and is needed as the armoured cable does not reach the site of the proposed new buildings after the demolition of the existing one. Additional armoured cable will be joined on at the box.
'Normal DIY' tools will be used in the workshop - saw, drill, vacuum cleaner etc.
I will look again at where the armoured cable exits the house to see if I can see if it is earthed.

 

[SaladFingers]

What underground junction is being fitted?
and is this necessary and accessible?

Could use a resin joint kit, then access isn't needed.

 

[PrenticeBoyofDerry]

Thanks for the swift replies.
The underground box will be a Pratley 3 way size 0

So what method is being used to comply to BS7671:2008 (526.3)
regarding to jointing of inaccessible joints? or will this be accessible?

 

[SaladFingers]

Thanks for the swift replies.
The underground box will be a Pratley 3 way size 0

So what method is being used to comply to BS7671:2008 (526.3)

Offer the guy some help instead of a post like that, it comes across as a little rude.

You know he's a diyer who's after help.

A better way to word it would be to say....

You need to comply to BS7671:2008 (526.3) with your selection of terminal boxes.

 

[PrenticeBoyofDerry]

What underground junction is being fitted?
and is this necessary and accessible?

Could use a resin joint kit, then access isn't needed.

They could and that is where I am leading! As I am not sure the OP is aware of the requirements.

 

[bernardgreen]

Have you considered extending the cable to the garage with the buried joint being a simple straight through joint and then taking a feed from the garage to the work shop. ( assuming the layout allows for this )

 

[PrenticeBoyofDerry]

Thanks for the swift replies.
The underground box will be a Pratley 3 way size 0

So what method is being used to comply to BS7671:2008 (526.3)

Offer the guy some help instead of a post like that, it comes across as a little rude.

You know he's a diyer who's after help.

A better way to word it would be to say....

You need to comply to BS7671:2008 (526.3) with your selection of terminal boxes.

rude: really moi
Don't like to sound rude but:

What distance is between the buildings and what size is the existing SWA? Might be worth considering doing away with it and starting afresh!

 

[riles]

Thanks again to all who have helped so far.
So regarding the underground supply and access to the junction box, I was simply going to mark its location with a plastic stake, but if this is undesirable I have two choices - either use a resin fill kit (I was aware of them, but had never used one); or try to make the original armoured cable reach the garage and then use an appropriate above ground box and then send the additional armoured cable underground to reach the workshop a couple of meters further on.

 

[viewer]

As you say "outbuildings" and no construction details, distances etc, then an alternative which is supported by many bodies would be to earth the armour at the house then make the first building TT by using a rod. The armour is not connected at the first building, only at the house. The next length of SWA would have the armour earthed to this first rod. At the second building the armour is not connected and a new rod provides the earth. And so on.
This is an alternative to the using of the armour as CPC for the whole system and the argument is that the potential difference between ground at the house end and at the farthest reach could be important. I won't make this a point of "being better" (although it solves several metal buildings problems) as only measurements would be useful, however, it may be easier for you as you only have to deal with one section at a time and don't have to join (electrically) the lengths of armour as you progress and may more flexibility in where the incoming/outgoing routes are positioned. It may help with the need for underground joints.

 

[JohnD]

how far is the building from the house?

will it have water or gas supplies with metal pipes from outside?

 

[riles]

The buildings will both be timber construction - the garage having a concrete floor, the workshop floor timber on top of concrete. The buildings will be about 12 metres from the house. The SWA armoured cable is 2.5mm twin core.