SWA or tails?

[HappyHippyDad]

I know I have started another thread in the past with an almost identical title but this one is asking different questions!

The DNO are moving the meter box and I will need to extend the tails to approx 8m.

The present earthing arrangement is TT, I have asked the DNO to change to TN-C-S and they have said they will do so if they can.

I have 2 questions:

1. Would you always use SWA when extending the tails on a TT due to their not being any fault protection (assuming Ra>1ohm) or would tails be acceptable? I personally cant really see it being ok to run tails through the house (under floorboards) on a longer run as it quite significantly increases the risk of an accident happening.

2. If using SWA would it be better to use 3 core, or 2 core and run a separate earth? The reason for asking is mainly due to concerns about how easy the SWA is to manipulate when getting it to the CU. Is 2 core considerable easier than 3 core to manipulate or is there not a great deal of difference? It will be 16mm2 (80A switch fuse)

Cheers all.

 

[telectrix]

use 3 core SWA. glanding into a metalclad CU should not pose any problems. obviously make sure the armour os earthed as well as using the 3rd core as cpc.

 

[Deleted member 26818]

Only need 3 core if TN-C-S.

 

[sparksburnout]

Regarding your point 1, I think it is a good one. I recently had a similar situation extending to a CU over a similar distance. The run was in a garage and could have theoretically been done in 25mm tails as it was all clipped direct from switch fuse to CU and mostly out of reach. However I decided to do it in SWA due to the environment, it just seems a more suitable selection method, and probably cheaper as well.

 

[westward10]

The armour is likely to be inadequate for bonding purposes whether TN-C-S or TN-S.

 

[westward10]

Only need 3 core if TN-C-S.

This is incorrect applies to TN-S also.

 

[bigspark17]

The armour is likely to be inadequate for bonding purposes whether TN-C-S or TN-S.

Not if bonding is ran to met at supply

 

[Toneyz]

You've still got to have a sub distribution circuit now to feed the existing d.b/c.unit,any way you earth it be it core/swa sep.earth etc with switchfuse.(isolation & protection)
what are the earthing arrangements of other installations in the street will give a guide if PME exists etc.

If it still has to be TT you may have to fit a S type/time delayed RCD to acheive disconnection times for the distribution circuit.

 

[Deleted member 26818]

Yes it would apply to TN-S.
However the OP has not asked for the supply to be changed to TN-S.

 

[westward10]

Yes it would apply to TN-S.
However the OP has not asked for the supply to be changed to TN-S.

Point taken I read your post as a general comment.