UK Summerhouse earthing

[BertySimp]

Hi all,

I am having a new summerhouse built at the end of my garden circa 50m from house consumer unit. House has TNCS earthing arrangement. I was planning to run a 10mm 2 core SWA cable to the summerhouse and put in an earthing rod and earth direct to that. Someone has just advised to run a 3 core and connect to house earthing. Which is the best option. Obviously would i would get a professional to connect etc but was going to do the majority of the cable runs etc myself. Need to run the cable before summerhouse is built S currently having a patio laid and cable will run under it.

please could someone advise which is the best and safest method.

many thanks in advance.
b

 

[James]

depending on the loading, 10mm might be big enough, but it might not.
I would suggest running a duct so the cable can be pulled through later.
it is often worth pulling a couple of network cables down at the same time.
cctv, wifi, bird box camera etc.

 

[BertySimp]

depending on the loading, 10mm might be big enough, but it might not.
I would suggest running a duct so the cable can be pulled through later.
it is often worth pulling a couple of network cables down at the same time.
cctv, wifi, bird box camera etc.

Thanks James, good idea with network cable.10mm 2 core has a rating of circa 80a. I thought that would be sufficient. It’s for a fridge, tv, small electric heater, a few sockets and lighting. May later run a 13a hot tub off the summerhouse CU at a later date. Just confused about best earthing method to go with as two people have said two different methods. With one saying I could not earth off the house TNCS.

 

[telectrix]

perfectly OK to use the house earthing. run a 3 core SWA. 10mm should be protected with a fuse/MCB of 50A.

 

[James]

at that distance, around 30A is the most you can push down 10mm and stay within 3% volt drop.
hot tub and heater combined could be 26A so it is not as much spare to play with as you might think.

Agree with @telectrix about the earthing arrangement.

 

[BertySimp]

at that distance, around 30A is the most you can push down 10mm and stay within 3% volt drop.
hot tub and heater combined could be 26A so it is not as much spare to play with as you might think.

Agree with @telectrix about the earthing arrangement.

Thanks everyone. So would you recommend 16mm SWA just to be safe?
[automerge]1597339775[/automerge]

Thanks everyone. So would you recommend 16mm SWA just to be safe?

Just found the guys message he sent regarding earthing, saying that if it’s for a hot tub or running water then i can't export TNCS earthing system to man cave from house.

 

[James]

cost difference is likely to be negligible in the scheme of things.
so bigger is better as they say.

I would recommend that you get the spark that will finally connect it to specify the cable type and size, route, method of burial, depth, marker tape etc. all agreed before purchasing anything.

 

[davesparks]

Thanks James, good idea with network cable.10mm 2 core has a rating of circa 80a. I thought that would be sufficient.
Just confused about best earthing method to go with as two people have said two different methods. With one saying I could not earth off the house TNCS.

You've missed some steps in your calculation if you managed to calculate that 10mm can carry 80Amps at a distance of 50metres!
At a guess 10mm might be OK for 32A at that distance.

Whoever told you you cannot use a TNCS earth to an outbuilding was talking nonsense.
[automerge]1597340244[/automerge]

Thanks everyone. So would you recommend 16mm SWA just to be safe?
[automerge]1597339775[/automerge]

Just found the guys message he sent regarding earthing, saying that if it’s for a hot tub or running water then i can't export TNCS earthing system to man cave from house.

No, I'd recommend carrying out the cable size calculation and volt drop calculation to work out what size cable is required.

It would be nice to hear the reasoning behind that statement about hot tubs and running water, I doubt very much they can support the statement with any regulation.

If a 3 core cable is used with a CSA of 10mm or greater then it will satisfy the requirements for main bonding and allow the use of the TNCS earth.

 

[cliffed]

No probs using Tncs,if no main earth bonding required.
Also TT May be advisable to supply hot tub.

 

[telectrix]

i'd use 10mm with up to 40A load. this would give a VD of 9V @ 40A over 50m, which is over the 3% for lighting, but that 3% came from the days where incandescent and fluirescent lighting was the norm. with LED lighting it's out of date. tin hat firmly attached to bone head.

 

[Ian1981]

Really all that matters is that the voltage is sufficient for the current operating equipment Such as led drivers which normally state an operating voltage of between 220-250 volts.
The 3 percent is a safe design value, the voltage could be around 245 volts say before you’ve even installed a sub main.
Then again it could be less.

 

[BertySimp]

Hi all,

I am having a new summerhouse built at the end of my garden circa 50m from house consumer unit. House has TNCS earthing arrangement. I was planning to run a 10mm 2 core SWA cable to the summerhouse and put in an earthing rod and earth direct to that. Someone has just advised to run a 3 core and connect to house earthing. Which is the best option. Obviously would i would get a professional to connect etc but was going to do the majority of the cable runs etc myself. Need to run the cable before summerhouse is built S currently having a patio laid and cable will run under it.

please could someone advise which is the best and safest method.

many thanks in advance.
b

I would just like to thank everyone for their help, support and advice. It is greatly appreciated.

 

[DefyG]

Not sure of actual figures but I think the CSA of the SWA of a 2core 10sqmm is greater than 10sqmm equivalent copper and can therefore be used as a TNCS bonding conductor.

 

[davesparks]

Not sure of actual figures but I think the CSA of the SWA of a 2core 10sqmm is greater than 10sqmm equivalent copper and can therefore be used as a TNCS bonding conductor.

The armour of a 10mm 2 core SWA cannot be used as a 10mm binding conductor, it isn't big enough.
You cannot directly compare the CSA of the steel armour with the required CSA of the copper because the conductivity of steel is approximately 8 times lower than that of copper so you need a steel CSA of approximately 80mm to be used in place of a copper 10mm bonding conductor.