600mm swa cable depth rule

[joehat]

I've always assumed this rule was the same under slabs or concrete, not just under soil Ect.
Am I correct as the regulation doesn't state so that's why I assumed it.

The reason being, I've just gone and quoted a job and another (electrician!!) quoted a lot less, I asked how much Ect and how he was doing it and he said he would cut a cap below the slabs and run swa to the shed. ??

 

[sparksburnout]

I agree with Welchyboy, this is a sticky one. I don't see how BS7671 could give specific depths for specific locations or purposes. I will put my tin hat on and say that 600mm is quite often unrealistic and possibly unnecessary. If the average spark working in the domestic arena quoted for the amount of labour involved he would never get the job. You have to use your common sense, if you are putting a cable under a garden that is going to be dug, then it needs to be deep enough to avoid being hit by "normal" activity, but what's normal? There is always the chance that ANY underground cable is going to be struck, including DNO cables. I recently came across a gas pipe installed to a new build with no marker tape at a depth of about 200mm, so even the supply authorities can't do it properly. What about a cable running round the perimeter of a building in a gravelled 100mm gap between the wall and paving? Are we really supposed to get it down to 450mm minimum? I think not. Sometimes its better to leave it clipped to walls/fence posts at ground level so its visible. And what if it is protected with an RCD? Should we approach it in the same manner that cables concealed in walls are? It is armoured cable at the end of the day.
I have come across loads of situations where is has been buried barely below the surface, probably because the contractor involved thought "well I can't get it 600mm so sod it". BS7671 tells us it should be deep enough to avoid being disturbed by "normal" activity, but it doesn't say what that might be. Sometimes the best you can do is make sure it is marked by tape and get it as deep as is practically possible, however deep that may be and at reasonable cost.

 

[Guest77]

I think he means that if its under someone's rose-bed then it needs to be deep enough not to be disturbed when they dig the muck in, but if its under paving slabs then its not likely to be disturbed and if it is then it will be obvious that it is there. That's what BS7671 say's isnt it?

Thats not the way I read the post.

 

[sparksburnout]

Thats not the way I read the post.

No I suppose you could easily read it as though he has quoted for 600mm below slabs. Would probably be major unnecessary upheaval.

 

[Guest77]

yup thats the way I read it.

 

[joehat]

Yet I have had a customer lately say they dug up gravel in a new build house and guess what BANG!! Straight through the armoured cable only about an inch below gravel, being the Sparks who installed the house electrics ( ************ ) being a big company it was interesting to hear!!

 

[sparksburnout]

Yet I have had a customer lately say they dug up gravel in a new build house and guess what BANG!! Straight through the armoured cable only about an inch below gravel, being the Sparks who installed the house electrics ( *********** ) being a big company it was interesting to hear!!

Difficult to imagine how shovelling gravel would result in going clean through SWA? Never tried it but it must take a damn good first effort. Maybe someone though it was a tree root, if it didn't have marker tape above it.

 

[joehat]

Difficult to imagine how shovelling gravel would result in going clean through SWA? Never tried it but it must take a damn good first effort. Maybe someone though it was a tree root, if it didn't have marker tape above it.

Digging up to plant a tree or similar.

 

[johnboy6083]

Personally, when I'm specifying projects, I use NJUG 2 as a guide to burial depths of services.

 

[djelectric]

'ELECTRICIANS GUIDE TO THE BUILDING REGULATIONS - BS 7671:2008+A3:2015' - 5.7.2 Fixed Cables (Page 80) states:

"Cables buried in the ground must be buried at a sufficient depth to avoid damage by any disturbance of the ground that is reasonably likely to occur. Cables should generally be buried at least 500mm, preferably deeper, below the lowest ground level and route marker tape used, laid along the cable route approximately 150mm below the surface. Buried cables must be steel-wire armoured or metal sheathed or enclosed in a conduit or duct. Double digging is likely to occur in a vegetable plot and, if cable must be laid in such a location, it should be at least 600mm deep.

A buried cable route should be identified by route markers and recorded on drawings retained with the Electrical Installation Certificate."

Hope this helps.

 

[djelectric]

Mind you, if its SWA below a solid slabbed patio wouldn't it be like treating any cables enclosed in conduit in a solid wall.. There's just as much risk of someone smashing a wall down with a hammer and hitting a cable as there is someone smashing up a patio..

 

[HandySparks]

Only in special locations, depths and heights are specified for buried and overhead cables.

Yep. Agricultural, 705.522, 0.6m min plus mech protection, 1.0m min where cultivated. Camping/caravan parks, 708.521.1.1, 0.6m min.

 

[ruston]

Agricultural and Horticultural Premises.
In selection and erection of wiring systems in relation to external influences 705.522 indicates depths required for buried cables.
notes 1 and 2. This is where the 600 mm and 1 metre come from. (in relation to vehicles and and mobile agricultural machines)
This is not conclusive.

Handy , you beat me to it , but I posted anyway.

Getting fed up of 3 mobile dropping out.

 

[Welchyboy1]

Well domestically with small swa circuits/submains, i will always try to clip it above ground as much as possible, i would omit rcd protection if the route is visible or buried sufficiently

if i have to bury it (avoiding high risk areas such as flower beds etc) and its not sufficiently deep, i normally just put tape above the cable run and rcd protect the swa cable

i think this is as sensible an approach as you can arrive at realistically, and is similiar to the regs with cabling buried in walls etc, if not a little safer as its obviously swa

anything serious then i would endevour to bury at an appropriate depth

 

[sparksburnout]

As above, you have to be realistic. I agree regarding RCD protection and maybe the regs should take account of this the same way cables in walls are. If someone has gone through a cable planting a tree, then either it was planted in a stupid place, or, more likely, the installer didn't use his common sense. Either avoid such routes or bury it appropriately. If you quoted for burying at 450mm in every situation you would either not get the job or it would be impossible anyway.

 

[joehat]

I quoted to go round the fence instead,
It was a new build, fcu would have fed from ring to shed with 1 double outside and one in shed with a light and this would have been 10-12 meters or so, 2 meters to shed if went under slab Ect.

Quoted £200
4 hours £120
Materials £80

He told me the previous quote £130 all in !!