Advice on trench depth for SWA - Answered!

I must admit I hadn't thought of frost, my main concern was not digging down to the sewer pipe.

Mike

I've just seen a video on youtube where an electrician ran SWA across a garden path by cutting a channel in it. Surely that's not allowed?

Mike

I'd definitely say it's not good working practice, at the very least. The cable is open to damage it's not designed to cope with.

I have seen this as a method of installing SWA cables “within” temporary concrete in construction traffic routes on construction sites abroad, and the cables really didn't last long at all.

the effects of ground freezing in the UK are less, putting less mechanical strain on the cable over time,

How does this differ from SWA routed above ground exposed to freezing temperatures?

Regards

BOD

perspicacious: 
 

the effects of ground freezing in the UK are less, putting less mechanical strain on the cable over time,

How does this differ from SWA routed above ground exposed to freezing temperatures?

Regards

BOD

Relative movement of materials in which the cable is embedded, with different expansion/contraction rates on freezing/thawing. Surface clipped or within containment/duct, it's only the cable itself.

Thanks for all the advice and ideas. It looks like I will be going for a 500mm deep trench then. At least it's quite short …

Mike

I've just seen a video on youtube where an electrician ran SWA across a garden path by cutting a channel in it. Surely that's not allowed?

The regulations often really aren't as simple as something ‘is allowed’ or ‘is not allowed’. There has been a definite trend over more recent years to move away from a rigid list of things to do and avoid, and more towards what needs to be achieved - leaving the designer with much more scope to so what's sensible in any particular situation.

In a way that's illustrated by the very title of the wirings regs. Back in the 1st Ed the wiring regs were called “Rules and Regulations” - and the Victorians had very specific ideas about the differenence between a Rule and a Regulation - a Rule demanded or prohibited (i.e. was a ‘thou shalt’ or ‘thou shalt not’) whereas a Regulation merely put conditions on things ( ‘xyz may be done on any day excepting the Sabbath’).  By the 8th Ed the word “Rules” had disappeared forever from the title.

There might even be situations - perhaps when running a cable over a bridge or some layered foundations - that cutting a shallow trench in the thin non-structural surface layers is a far better idea than going deeper. A simple set of rules really can't cover every situation.

   - Andy.

AJJewsbury: 
 By the 8th Ed the word “Rules” had disappeared forever from the title.

 

And now, to all intents and purposes, they are ‘requirements’ for electrical installations, and a British Standard, the ‘wiring regulations’ being merely a subtitle or colloquial title these days.