questions about SWA and earthing

raikky · 22 Sep 2014

just have some questions which im abit unsure about.

when wiring swa cable up to an outdoor socket, how do you actually earth the steel in the cable. the outside socket has 2 earth links. I assume one of the cores for the swa goes into 1 link, then what about the steel wire? does this connect up to the other earth by using some core to attach to the banjo ring?

the double socket is to power my pond pump and filter. they draw a combined 36watts. so would 1.5 or 2.5mm core be used?

btw, im not intending to do this myself, just curious. will have an electrician sometime later this year to install it all for me

gibbon234 · 22 Sep 2014

You need an swa gland kit and either: a crimp lug (and crimping tool), brass nut and bolt and a bit of cable to crimp and connect the banjo on the gland kit to the earth terminals; or a piranha nut instead of the nut bolt and banjo...

raikky · 22 Sep 2014

So is it better to use 2 core sea or does 3 core give more protection

flyingsparks · 22 Sep 2014

raikky said:
So is it better to use 2 core sea or does 3 core give more protection

Your electrician will know which is best to use in your particular circumstance.

sparkwright · 22 Sep 2014

Generally 3 core is better, as one core is used as the earth, and this also gets connected to the cable gland which then earths the armour.

It gives you a better earth, but also means if some of the armour should fail you will still have an adequate earth, as the core inside should hopefully remain untouched.

EFLImpudence · 22 Sep 2014

//www.diynot.com/wiki/Electrics:SWA

//www.diynot.com/wiki/Electrics:SWA_gland

ban-all-sheds · 22 Sep 2014

flyingsparks said:
Your electrician will know which is best to use in your particular circumstance.

And hopefully he will have heard of earth nuts.

JohnW2 · 23 Sep 2014

sparkwright said:
Generally 3 core is better, as one core is used as the earth, and this also gets connected to the cable gland which then earths the armour. ... It gives you a better earth, but also means if some of the armour should fail you will still have an adequate earth, as the core inside should hopefully remain untouched.

That's always been my (intuitive) view, but it seems that quite a lot of electricians think otherwise!

Kind Regards, John

ericmark · 23 Sep 2014

My colleague got demoted for using the SWA only when supplying a container as when the container was moved on a crane the SWA pulled out of the gland and live shorted against the container causing the container to become live while on the crane.

My colleague had not expected anyone to move a container while power was still connected.

So where there is a spare copper core to use as earth I would use it.

However in your case supply to a pond using TT may be a better option depending on the supply earth at the house. Ask your electrician as he may use an earth rod and not use the house earth at all.

bernardgreen · 23 Sep 2014

ericmark said:
However in your case supply to a pond using TT may be a better option depending on the supply earth at the house.

If there are fish in the pond then introducing the house "earth" into the water could be very un-comfortable for the fish. Unless the water is totally isolated from the surrounding soil any difference in potentials of the house "earth" and true ground will create some current in the water and fish are very sensitive to electrical current in the water around them.

Spark123 · 23 Sep 2014

ericmark said:
My colleague got demoted for using the SWA only when supplying a container as when the container was moved on a crane the SWA pulled out of the gland and live shorted against the container causing the container to become live while on the crane.

My colleague had not expected anyone to move a container while power was still connected.

Unless he was specifically told not to use the armour or he installed it without consent then he isn't at fault, I take it he wasn't a member of a union?

Spark123 · 23 Sep 2014

bernardgreen said:
ericmark said:

However in your case supply to a pond using TT may be a better option depending on the supply earth at the house.

Click to expand...

If there are fish in the pond then introducing the house "earth" into the water could be very un-comfortable for the fish. Unless the water is totally isolated from the surrounding soil any difference in potentials of the house "earth" and true ground will create some current in the water and fish are very sensitive to electrical current in the water around them.

I'm wondering if the equipment for ponds are double insulated / SELV hence earthing is matter less?

JohnW2 · 23 Sep 2014

Spark123 said:
I'm wondering if the equipment for ponds are double insulated / SELV hence earthing is matter less?

Yes, I thought exactly the same.

Kind Regards, John

sparkwright · 23 Sep 2014

ericmark said:
My colleague got demoted for using the SWA only when supplying a container as when the container was moved on a crane the SWA pulled out of the gland and live shorted against the container causing the container to become live while on the crane.

My colleague had not expected anyone to move a container while power was still connected.

Fascinating, and very, very unfair.

No one should have been attempting to move something like that with a live cable connected to it.

The same would easily apply to repositioning some very heavy machinery in a factory. Exactly the same.

JohnW2 · 23 Sep 2014

sparkwright said:
Fascinating, and very, very unfair.

Indeed, unless he contravened some local Code of Practice, or whatever, to which he was required to work.

Kind Regards, John

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questions about SWA and earthing

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