Why STEEL in SWA?

AJJewsbury: 
 

“Equivalent” to what exactly?

To my mind, to provide the same safety in the same circumstances - if an armoured cable remain ‘safe’ when hit by a spake/fork/mattock/pick/mechanical excavator bucket (by virtue of ADS) - the same attack on the duct/conduit system should be no less safe (e.g. if not by ADS then by some other means such as preventing the damage getting through to the cable).

To my mind a bit of plastic “twinwall” duct doesn't quite do that - at least in uncontrolled environments.

    Hi Andy not sure of your digging experience but anyone that puts a spake/fork/pick through any properly installed underground cabling has probably ignored the marker tape etc? With regards excavator buckets even the smallest machine will rip through a modest cable in half a second, there is no guarantee that electrical disconnection will occur.

Weirdbeard: 
 

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Weirdbeard: 
 

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Weirdbeard: 
 

AJJewsbury: 
 

Most of the difficulty was around glanding off the actual steel armour - trying to get everything aligned and tightened in a confined space seemed more like the less desirable aspects of being a plumber rather than an electrician. Split-con would have appealed - as then a simple stuffing gland could have been used and the copper outers just pig-tailed into the terminals, but as the cables go underground split-con isn't permitted any more. 

     

Hi Andy, you can run unarmoured cables underground if they are in a duct that provides normal mechanical protection, ie the duct is at an appropriate depth to any expected stress.

 

If the concern is offering additional protection to anyone who may mechanically stress a buried cable system then the additional protection should be via a 30mA RCD?

 

That must be Reg. 522.8.10 then. What is “equivalent protection?”

 

Z.

Any duct or conduit that is installed underground to contain a wiring system in accordance with BS7671.

“Equivalent” to what exactly?

 

Z.

Exactly equivalent to a duct or conduit that is buried to a sufficient depth to avoid reasonably foreseeable disturbance.  

522.8.10.

“Except where installed in a conduit or duct which provides equivalent protection against mechanical damage, a cable buried in the ground shall incorporate an earthed armour or metal sheath or both, suitable for use as a protective conductor”.

What defines exactly: “equivalent protection?"

Is this saying that any conduit or duct shall be as strong as any armoured cable or metal sheathed cable?

S.W.A. or M.I.C.C.

Z.

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Weirdbeard: 
 

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Weirdbeard: 
 

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Weirdbeard: 
 

AJJewsbury: 
 

Most of the difficulty was around glanding off the actual steel armour - trying to get everything aligned and tightened in a confined space seemed more like the less desirable aspects of being a plumber rather than an electrician. Split-con would have appealed - as then a simple stuffing gland could have been used and the copper outers just pig-tailed into the terminals, but as the cables go underground split-con isn't permitted any more. 

     

Hi Andy, you can run unarmoured cables underground if they are in a duct that provides normal mechanical protection, ie the duct is at an appropriate depth to any expected stress.

 

If the concern is offering additional protection to anyone who may mechanically stress a buried cable system then the additional protection should be via a 30mA RCD?

 

That must be Reg. 522.8.10 then. What is “equivalent protection?”

 

Z.

Any duct or conduit that is installed underground to contain a wiring system in accordance with BS7671.

“Equivalent” to what exactly?

 

Z.

Exactly equivalent to a duct or conduit that is buried to a sufficient depth to avoid reasonably foreseeable disturbance.  

522.8.10.

“Except where installed in a conduit or duct which provides equivalent protection against mechanical damage, a cable buried in the ground shall incorporate an earthed armour or metal sheath or both, suitable for use as a protective conductor”.

 

What defines exactly: “equivalent protection?"

 

Is this saying that any conduit or duct shall be as strong as any armoured cable or metal sheathed cable?

 

S.W.A. or M.I.C.C.

 

Z.

 

 

The slightest compromise of the plastic jacket of a sturdy SWA will render it defective.

Weirdbeard: 
 

Zoomup: 
 

Weirdbeard: 
 

Zoomup: 
 

Weirdbeard: 
 

Zoomup: 
 

Weirdbeard: 
 

AJJewsbury: 
 

Most of the difficulty was around glanding off the actual steel armour - trying to get everything aligned and tightened in a confined space seemed more like the less desirable aspects of being a plumber rather than an electrician. Split-con would have appealed - as then a simple stuffing gland could have been used and the copper outers just pig-tailed into the terminals, but as the cables go underground split-con isn't permitted any more. 

     

Hi Andy, you can run unarmoured cables underground if they are in a duct that provides normal mechanical protection, ie the duct is at an appropriate depth to any expected stress.

 

If the concern is offering additional protection to anyone who may mechanically stress a buried cable system then the additional protection should be via a 30mA RCD?

 

That must be Reg. 522.8.10 then. What is “equivalent protection?”

 

Z.

Any duct or conduit that is installed underground to contain a wiring system in accordance with BS7671.

“Equivalent” to what exactly?

 

Z.

Exactly equivalent to a duct or conduit that is buried to a sufficient depth to avoid reasonably foreseeable disturbance.  

522.8.10.

“Except where installed in a conduit or duct which provides equivalent protection against mechanical damage, a cable buried in the ground shall incorporate an earthed armour or metal sheath or both, suitable for use as a protective conductor”.

 

What defines exactly: “equivalent protection?"

 

Is this saying that any conduit or duct shall be as strong as any armoured cable or metal sheathed cable?

 

S.W.A. or M.I.C.C.

 

Z.

 

 

The slightest compromise of the plastic jacket of a sturdy SWA will render it defective.

 

 

Eventually, but I have only replied to this one 'cos I am v. disappointed by the new forum software. Even the thread on its defects was shifted. ?

Weirdbeard: 
 

Zoomup: 
 

Weirdbeard: 
 

Zoomup: 
 

Weirdbeard: 
 

Zoomup: 
 

Weirdbeard: 
 

AJJewsbury: 
 

Most of the difficulty was around glanding off the actual steel armour - trying to get everything aligned and tightened in a confined space seemed more like the less desirable aspects of being a plumber rather than an electrician. Split-con would have appealed - as then a simple stuffing gland could have been used and the copper outers just pig-tailed into the terminals, but as the cables go underground split-con isn't permitted any more. 

     

Hi Andy, you can run unarmoured cables underground if they are in a duct that provides normal mechanical protection, ie the duct is at an appropriate depth to any expected stress.

 

If the concern is offering additional protection to anyone who may mechanically stress a buried cable system then the additional protection should be via a 30mA RCD?

 

That must be Reg. 522.8.10 then. What is “equivalent protection?”

 

Z.

Any duct or conduit that is installed underground to contain a wiring system in accordance with BS7671.

“Equivalent” to what exactly?

 

Z.

Exactly equivalent to a duct or conduit that is buried to a sufficient depth to avoid reasonably foreseeable disturbance.  

522.8.10.

“Except where installed in a conduit or duct which provides equivalent protection against mechanical damage, a cable buried in the ground shall incorporate an earthed armour or metal sheath or both, suitable for use as a protective conductor”.

 

What defines exactly: “equivalent protection?"

 

Is this saying that any conduit or duct shall be as strong as any armoured cable or metal sheathed cable?

 

S.W.A. or M.I.C.C.

 

Z.

 

 

The slightest compromise of the plastic jacket of a sturdy SWA will render it defective.

 

 

It may after many years, or if the S.W.A. starts to operate like a water hose and cause problems at its lowest point perhaps. Or did you mean the M.I.C.C?

Z.

perspicacious: 
Shirley the box

Afrikaans connotation …………. oooh. Couldn't miss it.

Jaymack

Hi Andy not sure of your digging experience but anyone that puts a spake/fork/pick through any properly installed underground cabling has probably ignored the marker tape etc? With regards excavator buckets even the smallest machine will rip through a modest cable in half a second, there is no guarantee that electrical disconnection will occur.

A fair bit at a small scale - if by spade ?

Marker tapes are a nice addition, but ones anywhere near the surface seem to have a habit of going missing during landscape works by others - (personally I like to add a 2nd, deeper, closer to the cable, but the lack of depth over the cable means there's a lot less warning, so again can't be relied upon). BS 7671 requires marker tape (or equivalent) in addition to earthed armour (or equivalent) - not instead of.

Perhaps I should have mentioned the other favourite - metal spikes for fence posts - which can easily reach down 600mm - further if landscaping has lowered the surface - and they are of course bind to any buried warnings. These days with the trend for dividing the garden up into ‘rooms’ or adding pergolas etc. posts can end up anywhere in the garden not just on the boundaries.

Interesting point about the ‘cutting’ taking less than the ADS time (which could reasonably be up to 5s) - I'm not sure an excavator bucket would be sharp enough to cut cleanly through a cable without mangling the end enough to leave the armour at some point in contact with a core - but even if it did at least the excavator bucket wouldn't be live, even  if a few sq mm at the exposed end of the cable were. If the excavator bucket were still in contact with a live core, then it would almost certainly be in contact with the armour too - so ADS would be expected to operate, and in any event the armour shouldn't be left hazardous live.

   - Andy.

I'm not sure of the continental practices, though I think the steel would be much less usual than in the UK where it's a habit, if found at all.  

In Sweden the usual type of cable for direct burial (or ducts) has a copper screen as you suggest (e.g. here at a general hardware place, in 2.5 mm2 with up to 4 cores + screen).  

Copper has clear advantages for corrosion resistance if the sheath gets damaged, even if not as mechanically strong. 

 

That's very interesting. I didn't expect a single bare earth wire in addition to the braid. I've had a look around and the same approach seems to be used in a few other countries too - so not an unusual Swedish special.

I'm guessing the logic is that the braid is insufficient to act as a c.p.c. in general - hence the need for an additional single thick conductor. Would they cut the braid back at terminations and just connect the single earth wire? If so I guess the thinking is that at the point of impact the braid will carry the fault current - but only for a few cm until it's made contact with the main earth wire. The braid, being thin, will overhead to probably a far higher temperature than the insulation will survive (our usual restriction for sizing c.p.c.s) if still well below the melting point of copper, so sacrificing the cable at that point - but that's the damaged area anyway - and the remainder of the cable should survive and still be suitable for service once the damaged section is replaced.  I suppose it's not that different in principle to our BS 8436 (nail shield) cables.

Begs a question about our SWA cables, as the steel strands aren't necessarily in good contact with each other, so a fault involving just one or two strands of the armour might result in just a few strands taking the entire fault current for a considerable length of the cable.

   - Andy.

AJJewsbury: 
 

Hi Andy not sure of your digging experience but anyone that puts a spake/fork/pick through any properly installed underground cabling has probably ignored the marker tape etc? With regards excavator buckets even the smallest machine will rip through a modest cable in half a second, there is no guarantee that electrical disconnection will occur.

A fair bit at a small scale - if by spade ?

Marker tapes are a nice addition, but ones anywhere near the surface seem to have a habit of going missing during landscape works by others - (personally I like to add a 2nd, deeper, closer to the cable, but the lack of depth over the cable means there's a lot less warning, so again can't be relied upon). BS 7671 requires marker tape (or equivalent) in addition to earthed armour (or equivalent) - not instead of.

Perhaps I should have mentioned the other favourite - metal spikes for fence posts - which can easily reach down 600mm - further if landscaping has lowered the surface - and they are of course bind to any buried warnings. These days with the trend for dividing the garden up into ‘rooms’ or adding pergolas etc. posts can end up anywhere in the garden not just on the boundaries.

 

hi Andy, thanks for the reply, substantial landscaping works including the removal of existing warning tapes followed by unknown lengths of  steel spikes hammered randomly by DIYers is not reasonably foreseeable disturbance of the ground.

The Swedish cable isn’t cheap, how would you terminate it, with SY glands?

https://www.rselectricalsupplies.co.uk/cable-gland-kit-20s-cxt-sy-cable-gland-kit_846