SWA Termination Query

[Red Squirrel]

Hello Guys,

I wanted to try to get to grips with how SWA should be terminated before getting the sparky out!

Simple setup with SWA cable coming from consumer board to garden shed. Been having some issues with tripping back at the main supply board (garden shed breaker) so decided to investigate board in garden shed to find the SWA (3 core L,N,E) not having the armour earthed, this is a plastic enclosure for reference. The earth core is earthed at the earthing bar.

Back at the main supply board the armour is earthed to the earth bar from the gland (metal enclosure) - Should the armour be earthed at both ends or is this acceptable?

Thanks!

 

[binky]

One end is acceptable, both ends preferable.

 

[Red Squirrel]

One end is acceptable, both ends preferable.

Thanks. Straight to the point!

Very vague question but assuming the cable is not damaged in any way - by only having one end earthed does this increase the chances of a trip? I am assuming not if the external armouring is intact and not damaged. The end which is not terminated into the garden shed board is questionable with the armouring splayed out and not neatly cut back (it is not in contact with any of parts of the circuit).

On the other end of the scale assuming the cable was damaged only through to the armouring, would damp ground after heavy rain cause issues? Our problem seems to raise its head after a few days of heavy rain!

 

[Phoenix]

Very vague question but assuming the cable is not damaged in any way - by only having one end earthed does this increase the chances of a trip? I am assuming not if the external armouring is intact and not damaged. The end which is not terminated into the garden shed board is questionable with the armouring splayed out and not neatly cut back (it is not in contact with any of parts of the circuit).

No, only having one end earthed will result in higher loop impedance, which could in some edge cases make some overcurrent devices less likely to operate, if the fault itself has a significant resistance. (Thats a bit of an asside and not really revelant to your question)

But not earthing the far end will not on its own cause the RCD to trip in damp wehether, however an inproperly terminated SWA in an enclosure which is letting in water will and often folk that don't properly gland armoureds often end up making unsuitable joints as well

 

[Red Squirrel]

No, only having one end earthed will result in higher loop impedance, which could in some edge cases make some overcurrent devices less likely to operate, if the fault itself has a significant resistance. (Thats a bit of an asside and not really revelant to your question)

But not earthing the far end will not on its own cause the RCD to trip in damp wehether, however an inproperly terminated SWA in an enclosure which is letting in water will and often folk that don't properly gland armoureds often end up making unsuitable joints as well

Great thanks, that makes sense. We are investigating further today encase we find anything obvious before getting the sparky out - don't worry the power is off!

Will come back here if we find anything unusual!

 

[Red Squirrel]

Having investigated further we found a joint in the cable, thinking this was the obvious culprit from tripping after heavy rain we removed the rubber protective sheathing to find no signs of water or corrosion unfortunately! Although what we have found is the armour has not been joined to continue to the garden shed - so now we effectively have the armour (which is earthed at source) stopping where this join has been made.

My understanding is this isn't ideal but doesn't really change the situation in regards to finding the issue? ie. its no different to the armour being open ended at the box in shed? Nothing is ever straightforward!

 

[binky]

What is actually tripping and is that in the house or garage?

 

[NozSpark]

That is far from ideal, especially if it’s buried…. If that’s the quality of the work then I’d probably be looking to replace the entire run of cable.
IMHO though,,, you need an electrician to test and identify the cause of the fault rather than randomly “following your nose”,,, you may be right in your assumptions, but you could also be way off base

 

[kerching]

That joint is rougher than a rough thing that, in itself, is rough

 

[Phoenix]

That joint is rougher than a rough thing that, in itself, is rough

An Un-sanded dog kennel?

 

[Geoff1946]

I would guess that someone damaged the cable and didn't want to admit to it. So, bodge it, bury it and leave pronto.
A paving contractor I employed did exactly that to my telephone cable!

 

[Murdoch]

And each end of the SWA should be connected to earth too

So regarding the main board tripping - what is tripping? Mcb? Rcbo ? Rcd ?

 

[SPECIAL LOCATION]

I would think that a short time doing a few continuity and Insulation resistance tests would indicate what the actual problem is...??

I have no idea how you are going to prove anything without getting a competent electrician with appropriate test gear out to do a few tests and investigations???

Unless you do have access to, and know how to use, industry standard continuity and insulation resistance test metres??.

But as you haven't actually quoted any test readings that you have done on this suspect cable then it is a bit of guess work?

If the consumer unit end is TN-C-S and the remote end it TT then the remote cable armour and earth conductors would not be connected to the remote CU.

But as has been asked WHAT DEVICE IS TRIPPING???
MCB, RCD, RCBO??