Joining t&e to swa in weatherproof box

Manfredmann · Sep 9, 2012

I have had little experience with using swa, so if anyone out there could advise on a good adapt.box or junction box that allows for rear entry (phnaar), and if I should be using 2 core or three core swa ( I realise the armour is to be earthed even if I don't use it as CPC) as not sure if using a core as CPC is better practice than using the armour!
Also is it frowned on to join 10 mm t&e to 6 mm swa XLPE?
cheers.

Engineer54 · Sep 9, 2012

Also is it frowned on to join 10 mm t&e to 6 mm swa XLPE?

Depends on which cable is supplying the power... If it's the 6mm, no problem if it's the 10mm then you could well have a problem...lol!!!

richy3333 · Sep 9, 2012

Wiska boxes and earth clamps, failing that your wholesaler should be able to supply an adaptable box with DIN rail and bits

oldtimer · Sep 9, 2012

I had to connect a swa for the garage to the CU but it was short so I terminated it via its gland to a metal surface box it was a 2.5mm cable but I put in a 4mm T&E and even then ran a 6mm earth between the box and CU remember if there is no seperate earth then you need to make sure the glands are "Electrically & Mechanically" sound because when they were put in you did not have to tun a earth as you used the SWA as the earth you should also apply this mentality to conduit and micc

Johnny-G · Sep 9, 2012

richy3333 said:
Wiska boxes and earth clamps, failing that your wholesaler should be able to supply an adaptable box with DIN rail and bits

The 32a boxes that the earth clamps fit don't have rear knockouts so he'll have to (carefully) drill one & fit a grommet.

Manfredmann · Sep 9, 2012

Ok, might just use 10mm swa and keep everything straight forward! I've use wiska boxes before and liked them but never drilled the backs out of them, thought that the backs are quite thick so grommets might be a problem. Silicone to the rescue?! Any thoughts which size would be best to join 10mm in, shame about the lack of earth clamps on the larger boxes, piranha earth locking nut it is then.

D Skelton · Sep 9, 2012

Manfredmann said:
if anyone out there could advise on a good adapt.box or junction box that allows for rear entry

I have used one of these for that exact scenario:

[ElectriciansForums.net] Joining t&e to swa in weatherproof box

They can be purchased from TLC and they have both rear entry and enough space inside for both banjo's and termination of large cables.

Manfredmann said:
if I should be using 2 core or three core swa ( I realise the armour is to be earthed even if I don't use it as CPC) as not sure if using a core as CPC is better practice than using the armour!

It all depends on what CSA of CPC the armour is equal to, this table I find is very useful: View attachment SWA CSA.pdf

You then need to use the adiabatic equation to work out if the CSA of the armour is suitable for the circuit.

Manfredmann said:
Also is it frowned on to join 10 mm t&e to 6 mm swa XLPE?

No problem with that at all, as long as the breaker is the correct size to protect the lowest rated of the cables (taking into account any correction factors that may need to be applied). This calculation should obviously be carried out before the adiabatic equation.

SYKRAPS · Sep 10, 2012

Given the option I would always choose the 3 core SWA aswell as earthing the armouring of the SWA correctly. I lose count of the amount of times that I see poorly made off SWA cables, some electricians seem to feel that a gland and locknut is sufficient whether it is tight or not and don't seem to want to connect a slave earth to the lock ring.