Earthing to shed supply

[markadams]

Hi,

I was doing a CU change today when I checked one of the circuits which was supplying a shed. It came off a non-RCD 32a BS60898 and ran internally in 4mm T&E into an adaptable box which connected into 4mm SWA to run outside, then the same at the shed end.

The shed end has an RCD protected 2 way CU.

My concern is about the earthing, as the internal cable only has a 2.5mm cpc supplying the earthing for the shed.

Should I run a separate earth cable from the adabtable box to the CU as earth end and allow the Armour on the SWA to carry the earth outside.

The SWA is a two core cable.

It is a TNCS system.

 

[tomspark93]

Did the Zs db figure comply? If so then leave it.
Is there any bonding requirements in this shed? If not, then again leave it as it is.

 

[markadams]

Did the Zs db figure comply? If so then leave it.
Is there any bonding requirements in this shed? If not, then again leave it as it is.

The shed is an empty wooden cabin with wooden floor so no bonding required, the Zs values are within tolerance but only just.

 

[Spoon]

I presume that due to the installation methods of the 4mm T&E and the 4mm SWA that a 32A breaker is ok?

 

[sparksburnout]

What are they using power for in the shed? If your worried why not drop it down to a 20A MCB?

 

[markadams]

What are they using power for in the shed? If your worried why not drop it down to a 20A MCB?

Not concerned about the 32a MCB as it is 4mm clipped direct, my only concern was the earthing as I would always use the SWA Armour from CU to CU.

 

[Dave OCD]

I thought 4mm T&E had a 1.5mm CPC ? Regardless of that though as long as the Zs is low enough it's fine. If the SWA part of the supply is relying on the armour for CPC and has been there a long time I'd check under the gland shroud at the supply end to make sure the armour isn't corroding - seen this many times.

 

[markadams]

If the SWA part of the supply is relying on the armour for CPC and has been there a long time I'd check under the gland shroud at the supply end to make sure the armour isn't corroding - seen this many times.

The Zdb is 0.62 but good advice on the possible rust, I need to go back tomorrow so will have a look.

 

[Dave OCD]

Yeah it's worth a look just for peace of mind Mark. 0.62 seems fine to me though.

 

[markadams]

Yeah it's worth a look just for peace of mind Mark. 0.62 seems fine to me though.

Seemed good to me too (-:

 

[conrad]

Assuming the swa is 3 core and one conductor used as cpc?

 

[davesparks]

Assuming the swa is 3 core and one conductor used as cpc?

No, he's already stated it's 2 core