S.W.A. Armour Earthing.

davezawadi (David Stone):

As many have said on here many times the sheath should not be considered insulation, it is mechanical protection. The core plastic is insulation, the bedding layer is not, just packing, so the armour is an exposed conductive part even if sheathed. is plastic-coated metal trunking or conduit an exposed conductive part? Yes, because unlike the cores it is not insulation tested with a water bath at manufacture, and whatever YOU do, may have defects you have not noticed. Is this part of an EICR, because this should be a code 2, but is obviously easily fixed with a new metal gland etc. The plastic hoods over glands are not insulation, they can easily be pulled back, they are environmental protection for the armour.

Yes, but does a ECP have to be insulated, or merely capable of being touched?


I agree that the plastic hoods are not insulation - it is far too easy to pull them back.


And at this stage, with mention of pulling back hoods, I think that I shall stop. ?

davezawadi (David Stone):

You do try to have competitions sometimes!


As many have said on here many times the sheath should not be considered insulation, it is mechanical protection. The core plastic is insulation, the bedding layer is not, just packing, so the armour is an exposed conductive part even if sheathed. is plastic-coated metal trunking or conduit an exposed conductive part? Yes, because unlike the cores it is not insulation tested with a water bath at manufacture, and whatever YOU do, may have defects you have not noticed. Is this part of an EICR, because this should be a code 2, but is obviously easily fixed with a new metal gland etc. The plastic hoods over glands are not insulation, they can easily be pulled back, they are environmental protection for the armour.

The black outer S.W.A. covering is an electrical insulator. If people want to tamper with shrouds then that is wrong and could be dangerous. They are not that easy to pull back, they are a pig to put on most times-a very tight fit.  We can't excuse people tampering and dismantling electrical equipment. They are taking a risk.


The reason for the question is this:


I came upon a long length of 2.5mm2 3 core S.W.A. running through trees at high level and out of reach recently. The supply was TT. The cores were connected as L. N. and C.P.C. The armouring was not connected at each end, just left disconnected at plastic enclosures.


 I alerted the site owners of the defect, then began to wonder about which regs. actually apply here.


The outer sheath of S.W.A. cable is made of P.V.C. a well known electrical insulator. So the steel armour is not exposed.

cab_6943x_1.pdf (electricalcounter.co.uk)


Z.

 

Zoomup:

The reason for the question is this:

I came upon a long length of 2.5mm2 3 core S.W.A. running through trees at high level and out of reach recently. The supply was TT. The cores were connected as L. N. and C.P.C. The armouring was not connected at each end, just left disconnected at plastic enclosures.


 I alerted the site owners of the defect, then began to wonder about which regs. actually apply here.

My concern would be about the cable supporting it's own weight and being protected from abrasion. Earlier this year, A BT engineer knocked on the door and asked permission to replace a neighbour's cable which had been abraded where it passes through the canopy of one of our trees.


Would H07RN-F have been suitable? If so, I cannot see why the presence of armour would make it any less safe. 522.8.4 may apply.

AJJewsbury:


We are a bit double standarded (is that a word?) though - on one hand we claim the sheath isn't an adequate insulator, but then when we create a TT island we typically rely on the sheath (and boot over the gland) to prevent contact between two different earthing systems (which under some conditions can differ by full mains voltage).

I don't agree that a "boot" over the gland does the job in the case that the armour is not earthed as an exposed-conductive-part or protective conductor. Suitable insulation such as cold shrink sleeving (that can only be removed by destruction - Regulation 416.1), is far more appropriate, and indeed the actual requirement of BS 7671.


Think about the fact that the person you are trying to protect isn't just someone who is neither skilled nor instructed, but perhaps the "next spark in the queue" ... and the fact that the EAWR and CDM Regs apply in almost all circumstances to the work being undertaken by that person, or the designer or both ... and if you decided to take that approach, you're the designer.

Kelly Marie Angel:

I would say that unless strictly prohibited ALWAYS earth it  after all its in very close proximity to live conductors and if someone slices thru the cable by accident it lessens the chances of the person getting a fatal shock. Case in point my dad sliced thru an swa cable whilst making holes for fence posts he didn't feel a thing but it took out  all 3 of the main fuses for the  building

Quite right Kelly, I always earth the armour of any underground mains S.W.A. cable for safety reasons. I recently came upon a customer that had had a new fence installed. A Metpost had pierced the S.W.A. cable underground but the circuit protective device tripped off thus preventing danger in the garden. Just think of a dog peeing up a live Metpost, or a child retrieving a lost ball by the Metpost. Not nice.


Z/

Phased:

522.8.10

Yes this applies to my case 1.


Z.

Igkenyon:

AJJewsbury:


We are a bit double standarded (is that a word?) though - on one hand we claim the sheath isn't an adequate insulator, but then when we create a TT island we typically rely on the sheath (and boot over the gland) to prevent contact between two different earthing systems (which under some conditions can differ by full mains voltage).

I don't agree that a "boot" over the gland does the job in the case that the armour is not earthed as an exposed-conductive-part or protective conductor. Suitable insulation such as cold shrink sleeving (that can only be removed by destruction - Regulation 416.1), is far more appropriate, and indeed the actual requirement of BS 7671.


Think about the fact that the person you are trying to protect isn't just someone who is neither skilled nor instructed, but perhaps the "next spark in the queue" ... and the fact that the EAWR and CDM Regs apply in almost all circumstances to the work being undertaken by that person, or the designer or both ... and if you decided to take that approach, you're the designer.

In my case 2, the high level run S.W.A. entered an all insulated enclosure unglanded and not connected to earth at both ends. The three core S.W.A. was connected as L., N. and C.P.C. 


Z.

Zoomup:

 

In my case 2, the high level run S.W.A. entered an all insulated enclosure unglanded and not connected to earth at both ends. The three core S.W.A. was connected as L., N. and C.P.C. 


Z.

In this case, an undetected fault to armour might leave the armour "live" and wouldn't necessarily be detected by the tests prescribed in BS 7671 (insulation resistance test to cpc or earth won't pick it up) - you'd specifically need to test to armour. What if the outer sheath becomes damaged at some point?


Thinking about the permutations logically, I'm tending towards it being negligent, in most cases, to avoid earthing armour of a cable operating at low voltage, unless some other precautions are taken.