One For The Sparks

[Parm]

Im planning a new workshop build this summer and also want to upgrade the electric supply, this bit will be done by an electrician Mate

The new cable has to feed an outside store with a chest freezer plus a 2kw heater, then on to my barn which has 2 off 2kw heaters and then finally to my workshop with the usual range of stuff, none of which is run at the same time

Each of the three buildings has its own consumer unit

The total run will be about 30 meters

What size of armour cable will I need?

Is 10mm enough or should I go to 16mm?

 

[dobbslc]

Bigger is better says our Murican friends!
A single 2kw heater will draw about 8 amps.
I would definitely go with the 16mm swa, get a 2 core to save money and use the armoured as the earth. Make sure it's glanded into a metal containment and you'll be ok.

 

[dobbslc]

Been up late watching Forged in Fire Parm?

 

[normspanners]

Could you go into the first and second buildings with shorter lengths, ie more chance of used from e bay or getting offcuts from wholesalers, then use biggest you can find? ie for first run 16 or even 25 or maybe even 4 core 10 and use two cores for line neutral then reduce sizing, maybe as you go, you can always use bigger cable with smaller mcb but obviously not the other way, but you could also have reducing mcb's in each junction, as long as the last thinner run is adequately protected by the last mcb in line.

 

[WorkshopChris]

Do you know if you are on a PME supply where the earth and neutral terminal are combined by your supplier at the incoming before the house distribution board or do you have a earth rod?

 

[normspanners]

Yes Chris I was thinking about seperate earth ie exporting or not

 

[Parm]

Could you go into the first and second buildings with shorter lengths, ie more chance of used from e bay or getting offcuts from wholesalers, then use biggest you can find? ie for first run 16 or even 25 or maybe even 4 core 10 and use two cores for line neutral then reduce sizing, maybe as you go, you can always use bigger cable with smaller mcb but obviously not the other way, but you could also have reducing mcb's in each junction, as long as the last thinner run is adequately protected by the last mcb in line.

Yep, definitely

The first run to the store room is just under 8 meters, the second run to the barn is around 10m and then on to workshop

So yes I could probably buy off cuts to do what I need

 

[Parm]

Do you know if you are on a PME supply where the earth and neutral terminal are combined by your supplier at the incoming before the house distribution board or do you have a earth rod?

I’ve no idea?

Educate me, why is this important / relevant

 

[dobbslc]

It's to do with earthing, you are not allowed to export the earth "outside the equipotential zone" of the building if you are on a
PME/TN-CS supply. You should seperate the earth from the house and use an earth rod at the workshop end.
If you are on a TN-C or TT system you can use the earth from the main building.
Bloody confusing!
Get a photo of your service head/ main fuse and we should be able to tell you what you have .

 

[Parm]

It's to do with earthing, you are not allowed to export the earth "outside the equipotential zone" of the building if you are on a
PME/TN-CS supply. You should seperate the earth from the house and use an earth rod at the workshop end.
If you are on a TN-C or TT system you can use the earth from the main building.
Bloody confusing!
Get a photo of your service head/ main fuse and we should be able to tell you what you have .

Ok, just had a look, there’s an earth block with PME written on it.

The neutral incomer goes into a little black box which split to feed the meter and gives an Earth output to a grey box marked PME. From here the earth goes to the fuse box

Earth and neutral are definitely combined

 

[dobbslc]

Ok you'll probably need to put a rod in and seperate 30ma RCD's in the various buildings, although I had a supply to my garage for 18 years earthed from the house without a rod and it didn't kill me ......

 

[Parm]

Next question

So do I only need 2 core 16mm swa ?

And the earth will be a rod in the ground at the workshop end?

 

[Screwdriver]

In my experience if you ask ten different people you'll get ten different answers. Earthing is just one of those contentious topics no one really will agree on. Take an aggregate of opinion then make your own mind up.

As it happens I have a fair bit of 16mm 3 core SWA and "shed land" is now fully populated so it's going spare. Let me know your required length(s) and I'll see what I've got....

 

[Parm]

In my experience if you ask ten different people you'll get ten different answers. Earthing is just one of those contentious topics no one really will agree on. Take an aggregate of opinion then make your own mind up.

As it happens I have a fair bit of 16mm 3 core SWA and "shed land" is now fully populated so it's going spare. Let me know your required length(s) and I'll see what I've got....

I don’t know much about electrics, was just trying to get familiar with things before my sparky mate gets involved. Nothing like being in a conversation that you don’t understand

Looking for he bit about 15m and the other about 19m

 

[daedalusminos]

As dobslc says, you only need 2 core and use armour as earth (assuming the resistance of the armour is low enough which it probably will be). Sounds like you need to sink a rod (or most likely 2 stacked) - use an SDS drill. You'll probably only need the rod for the furthest building so the armour will export the house earth to the first two. In that case you need to take the earthed armour into the furthest building and then isolate - the rod will be your electrical earth in this furthest building.

It's a good idea to use RCBO's so each circuit is protected individually.

 

[Parm]

As dobslc says, you only need 2 core and use armour as earth (assuming the resistance of the armour is low enough which it probably will be). Sounds like you need to sink a rod (or most likely 2 stacked) - use an SDS drill. You'll probably only need the rod for the furthest building so the armour will export the house earth to the first two. In that case you need to take the earthed armour into the furthest building and then isolate - the rod will be your electrical earth in this furthest building.

It's a good idea to use RCBO's so each circuit is protected individually.

I shall show this to my sparky mate. He is the one doing all the doing

I shall just be passing tools and making tea on this project

 

[Parm]

On another note

I just got lucky

My neighbour runs a big ground works and utilities firm and his yard is in the village.

Went along to see him and asked if he had any cable, turns out he’s got a yard full of the stuff.

So after a quick look around I found some 16mm SWA. It’s on one of those big rolls must be at least half a drum.

His telehandler man has just dropped the drum on in my garden. Use what I need then give him a bell and arrange collection

He won’t take any money

 

[Ashley Burton]

On another note

I just got lucky

My neighbour runs a big ground works and utilities firm and his yard is in the village.

Went along to see him and asked if he had any cable, turns out he’s got a yard full of the stuff.

So after a quick look around I found some 16mm SWA. It’s on one of those big rolls must be at least half a drum.

His telehandler man has just dropped the drum on in my garden. Use what I need then give him a bell and arrange collection

He won’t take any money

Sounds like a result!

 

[normspanners]

Right----------- all down to parm for a swa party !!
As far as I understand it,
The problem with exporting the earth is, if there is a earth fault in the workshop it can be then transferred to the house through the earth cable or if you then use an earth rod in the earth at the garage as well as it is connected by an earth cable to the house and there is any potential difference in the ground, that issue can be transferred to the house and you can end up with nuisance tripping or no tripping of the rcd in the house depending on the fault but the actual problem is in the garage /workshop or in the ground around the garage etc