Earthing SWA

[gerry.slater65@]

I have had many ideas on this subject,could someone please tell me the correct way.
I am running about a metre of 3 core 2.5mm cable between a CU and an Isolator. Both boxes are metal.
One of the cores will be used as the Earth.
Do I need to run a seperate cpc,if so how do I connect it and where?
If someone could explain this SIMPLY for me it would be much appreciated.

Thanks

 

[Spudnik]

The glands that you will need to use to terminate the SWA at both ends will contain an item called a banjo. The reason its called that is because it looks like one.

Now, when you have drilled the hole for the gland into the CU, fit the gland into the enclosure and before you fit it with the supplied nut, slide the banjo on first, then the nut.

After its tight drill through the enclosure with a 6mm bit, in line the small hole on banjo and take a fly lead from the earth bar to this, with an eyelet yellow crimp and bolt up with a roofing bolt.

Sorted.

Its best practice to earth the SWA at supply end, ie cu.

Hope that helps and is reasonably clear!

 

[gerry.slater65@]

Thanks very much,it's a great help.

 

[Archie]

Hi
Don't forget that you should only use one of the cores as an earth OR the armouring, never both.
Due to the two earth paths, which could be of different resistances, there is a phenomenon where you could get circulating fault currents under fault conditions. What is recommended is to earth one end of the armouring only and insulate the other end, or just use a TRS gland on the inner part of the cable only.
Saying that...
I've never come across any evidence of these circulating fault currents myself and wonder if it a theorum rather than something seen in real life?

 

[KNIPEX]

well ive never heard of this before, im sure many will agree.

if you use a three core swa with one core earth, how do you earth the armourings then??????

 

[Spudnik]

The armour must be earthed.

No different from using earthed metallic conduit with twin and earth buried in a wall.

 

[benji]

Please don't use a roofing bolt use a setscrew/washers/nut, bond both ends via earth tags(bango) the cable manufacturers calculations are made assuming that both ends are bonded to earth ,running a supplimentary cpc with a swa is acceptable, if its all bonded to earth you won't get any circulating fault currents flowing .When you use single core swa you also bond both ends to earth in fact only a QUALIFIED ELECTRICAL ENGINEER can ask for the cables to be insulated from earth at one end
yuors benji

 

[bcm_spark]

Why not use a roofer??

 

[benji]

because they look crap, for earthing they are crap, iv'e had insurance companies condemn them, and if there is any dampness around you tend to get a reaction between the brass and the galv.
yours benji

 

[Chappers]

because they look crap, for earthing they are crap, iv'e had insurance companies condemn them, and if there is any dampness around you tend to get a reaction between the brass and the galv.
yours benji

That's a bugger, just got the parts fairies to order us bags of roofing bolts at work precisely for armoured cable... I blame the Spark in Chief, he's teaching me bad ways.

 

[not clever]

Use Piranha earth nuts they are good for keeping IP integrity of enclosures, bin the banjos.
http://www.earthingnuts.co.uk/pdf/fitting_instructions.pdf
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Oh & earth the armour even if you have used a conductor as a cpc.