Why STEEL in SWA?

Perhaps in certain situations a length of underground Hi-Tuff cable run in steel scaffold pole would comply. Especially if the whole lot was to be run under a concrete drive or patio, with suitable warning tape over it of course.

Z.

Over the years there’s been a few times we needed to get a pipe or cable under a private road, not having a mole we dug a trench then drove a scaffold tube with a spike off a tractor front end loader adapted to go into the front end of it under the road with a sledge hammer.

When needs must and all that ?

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Perhaps in certain situations a length of underground Hi-Tuff cable run in steel scaffold pole would comply. Especially if the whole lot was to be run under a concrete drive or patio, with suitable warning tape over it of course.

I think that there is a distinct danger of the pudding being over-egged here.

When we had the concrete, etc. relaid at the back of the house, provision was made for Mrs P's fountain, which is visible from the kitchen window (and my lathe room). 

The ground worker was instructed to lay some black ducting, but in the event, he used a bit of blue water pipe. I couldn't help feeling that putting in some SWA to the pump was a waste of effort. Said pipe sits in the ballast an inch or so below the block paving. Frankly, I think that any act which could disrupt the cable would be either reckless stupidity or malicious.

ETA: here it is. And yes, that is an effin' fox. ?

In the final case the SWA had to terminate into  wiska box with threaded entries, so glanding to the cable first wouldn't have worked

Shirley the box could have been rotated onto the SWA gland before the other cable entries were fitted?

Regards

BOD

Shirley is a nice girl BOD, doesn't go for cricketers or plastic boxes at all!

Had the wiring made the fountain live, it might have fixed the fox problem.?

Just needs the pond to be made the stinger part of an electric fence.

Probably a bit of fig 8 speaker cable in an off cut of  hose pipe would do for a few hundred watts of pump , but it is not in the high consumption style that our society requires. 

Abroad there are folk doing HV in the wilds and not worrying about armours

(mind you how many in the UK would dare to wind their own transformers and impliment an HV transmission in the way this chap has http://ludens.cl/paradise/turbine/turbine.html)

Quoting from half way down the page. My own DIY feels quite tame now.

The line consists of two 16mm conduits, each carrying a single 1.5mm2 wire, of the common household type that has a PVC insulation rated for 600V. I will run this line at 2kV between wires, with a center connection at ground potential, so that each wire sees only 1kV over its insulation plus the conduit. That should be safe even if water gets into the conduits! The line was provisionally laid over the forest floor, but will be buried for safety by Gabriel. Anyway I will use it at 220V only, with low power, until the transformers are ready.

Shirley the box could have been rotated onto the SWA gland before the other cable entries were fitted?

In this particular case not without undoing a substantial chunk of the existing… (and even then I'm not sure I'd be happy - what are the chances of the gland tightening into the box leaving the box at quite the correct angle to fit to the wall - rather than screwing the box to the wall imparting a twist onto the cable.)  Sure better planning could have avoided the problem, but I can't help feeling it might have been better not to have the problem in the first place.

It was just a thought.

   - Andy.

AJJewsbury: 

I quite agree the DNO's rules require an earthed(ish) screen - effectively BS 7671 does too  for buried or likely to be damaged cables (if anything more strictly as it must be PE not N) - my question was if the DNO's can achieve that with copper instead of steel these days, why can't we?

   - 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. 

AJJewsbury: 
 

It sounds like you are installing a wiring system with the anictipation that the mechanical protection is likely to be compromised?

That's always a risk with hidden cables in situations where digging/nailing/drilling is to be anticipated - I don't know of any wiring or containment system that would mechanically resist that. Hence BS 7671's requirements for concentric c.p.c.s or (for internal situations) additional protection by 30mA RCD.

   - Andy.

Hi Andy, thanks for the reply, I was thinking about the need for cables, conduits, and ducts to be buried at a sufficient depth to avoid being damaged by any reasonably foreseeable disturbance of the ground. 

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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.