SWA termination in CU

[pcboffinuk]

Found this one today:

The pic isn't great but the installer earthed the swa that runs down the garden to a greenhouse by taking about 1/4 of the armour, twisted and insulated, to the earth terminal.

He also covered it in black insulation tape, probably to hide the evidence .

I will certainly be redoing this, probably using an adjacent adaptable box.

However, although I thought (and still think) it was crap and should be ripped out, I then wondered if could be argued that it was 'compliant'.

From tables, the equivalent csa of that armouring would be 15mm, so even 1/4 or 1/5th of it would still be greater than 1.5mm.

Add to this that its a TT supply with a Ze of 20Ω at the distribution board, and I guess it becomes more a question of quality of workmanship rather than safety? I haven't tested it at the remote end but assuming that Zs was less than 30Ω then would that make it compliant?

The circuit is off at the moment anyway and the cable may have to be replaced because of voltage drop as the greenhouse is some way down the garden and I haven't got round to doing the calcs yet (busy sorting out all the other nice surprises).

However, would be interested to hear more experienced views.

Gavin

 

[Adam_151]

Remember you'd have to convert to copper equivelent values, but yes if it was TT and properly RCDed then I'm sure the adiabatic would return a suitablely small value for cpc size

Note however that with mechanical breakers (rcd+mcb) a high Z is preferable if you want a small cpc, because they are constant operating time, so small I gives small I²t

(fuses, its the otherway round, once you have a low enough EFLI to clear the fast enough (like at least 0.1 sec and quicker) its I²t thats constant, but when the fuse blows slowly the energy being dispated in the fuse has time to excape... do it fast enough this stops happening and I²t levels off towards a constant)

 

[securespark]

 

[Steve]

installer probably thought it was split concentric

 

[pcboffinuk]

installer........

.........thought

Not sure those two words can be used in the same sentence in this case

Thanks for the replies, particularly Adam showing his extensive knowledge as always

I have to say I've learnt more on this job than on any number of courses or book reading.

I will save the other questions for new topics to avoid this becoming too long - I'm sure I'm not done finding questionable methods

Gavin

 

[streetlighter]

Ive seen that done many times before minus the sleeving with the armour just twisted up and run into an earth block.

 

[C&GStudent]

Ive seen that done many times before minus the sleeving with the armour just twisted up and run into an earth block.

I have seen a few TN-S's where the armour, (all of it), has been terminated into the earth terminal in the cutout in a similar fashion to the pic in the OP.

Forgive if that's normal practice.