UK Swa as main earth ?!?

DJP1997 said:

So I have turned up on a job… someone previously has installed a 120mm 2 core swa from the meter to a barn building 160m away and them split off for the house and barn building in 25mm tails and have used the armour on the sea as the main earth.

Both ends of the swa have been terminated badly, the ze reading is 0.80 and the armour csa isn’t large enough to be use as the main earth.

I have calculated the for that distance a 70mm saw should have been used and then in that case the csa of the existing swa would be sufficient.

I’m conflicted now if I should make off both ends of the existing swa and if I get a low enough reading continue to use the armour as the main earth or to convert all 3 building that are fed from it to TT systems.

It’s a mess and the customer refused to put in the new correct cable… so what are your thoughts ??

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westward10 said:

What is the earthing system?

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westward10 said:

What size of main protective bonding is required?

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DJP1997 said:

So I have turned up on a job… someone previously has installed a 120mm 2 core swa from the meter to a barn building 160m away and them split off for the house and barn building in 25mm tails and have used the armour on the swa as the main earth.

Click to expand...

DJP1997 said:

Both ends of the swa have been terminated badly, the ze reading is 0.80 and the armour csa isn’t large enough to be use as the main earth.

Click to expand...

DJP1997 said:

I have calculated the for that distance a 70mm swa should have been used and then in that case the csa of the existing swa would be sufficient.

Click to expand...

DJP1997 said:

I’m conflicted now if I should make off both ends of the existing swa and if I get a low enough reading continue to use the armour as the main earth or to convert all 3 building that are fed from it to TT systems.

Click to expand...

DJP1997 said:

It’s a mess and the customer refused to put in the new correct cable… so what are your thoughts ??

Click to expand...

westward10 said:

The armour of a 120.0 two core will support a maximum of 10.0 main protective bonding from a TN-C-S system.
The size of main protective bond is not dictated by the size of this submain so I

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westward10 said:

The armour of a 120.0 two core will support a maximum of 10.0 main protective bonding from a TN-C-S system.
The size of main protective bond is not dictated by the size of this submain so I don't understand why you say 70.0 is fine but 120.0 is not.

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UNG said:

How much further are you going from the split to house and barn distribution

That does need sorting the 951 clamp is not the way to earth an SWA cable

What numbers are you using to get to this solution

It will tidy up the cable termination and at least one end of the SWA will need earthing

If the correct cable is the 70mm you say then I think you may need to revisit your calcs and take into account the whole installation as I don't believe you are looking at the total volt drop through to the final circuits

Is the SWA in a duct, if it is you could just pull in a suitably sized earth cable

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UNG said:

How much further are you going from the split to house and barn distribution

That does need sorting the 951 clamp is not the way to earth an SWA cable

What numbers are you using to get to this solution

It will tidy up the cable termination and at least one end of the SWA will need earthing

If the correct cable is the 70mm you say then I think you may need to revisit your calcs and take into account the whole installation as I don't believe you are looking at the total volt drop through to the final circuits

Is the SWA in a duct, if it is you could just pull in a suitably sized earth cable

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westward10 said:

It isn't the main earth it will be a cpc. If your main protective bonds need to be 35.0 then no it isn't adequate so you need to establish the bonding csa.

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timhoward said:

It should be a cpc, but reading his post it sounds as though the SWA heads off before the consumer unit or any protective device and he essentially has 160mm meter tails!

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timhoward said:

A diagram would be worth 1000 words in this thread. I suspect it needs tidying up at the origin to include an OCPD, some adiabatic calcs to determine CPC requirements, then considerations of bonding requirements the far end.

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timhoward said:

It should be a cpc, but reading his post it sounds as though the SWA heads off before the consumer unit or any protective device and he essentially has 160m meter tails!

I think that is why it’s being called the ‘main earth’.

A diagram would be worth 1000 words in this thread. I suspect it needs tidying up at the origin to include an OCPD, some adiabatic calcs to determine CPC requirements, then considerations of bonding requirements the far end.

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