How deep for main incomer?

[cardinal]

Evening all..

A friend of a friend has had a very lucky escape. Whilst attempting to put up a new fence, he smashed a fence post straight through his main incomer apparently. He says it was no more than 200mm in the ground, and to add insult to a very near serious injury or worse, they have sent him a bill for nearly £900 for the repair!

Anyone know of any reg's or guidelines on minimum depths? I have told him to seek legal advice before doing anything else, but was just interested. Good job it werent a metal shovel or something eh!

 

[ian.settle1]

Who has quoted BS:7671.??? 600mm is the nominal trench depth for cable laying. Normally the cable manufacturers will also quote this depth, when stating current ratings of cables for direct burial....

I've used this depth for so long now, that if it is in the BRB, ....I've never noticed it ...lol!!

ian in this posting before rocker

Re: How deep for main incomer?

Don’t think there is any specific depth in 7671, but most people seem to work on 600mm. The important thing is that it should not be damaged by using a spade etc.

However a old DNO mate told me that they had to work to

LV
Footpaths/Driveways, etc 450mm
Across Roads--------------600mm
Along Roads---------------600mm
Agricultural----------------910mm </SPAN></SPAN>

Not sure if that’s the case tho. ​

 

[mechelec]

latest cable depth spec from CN is

cables in footpaths or road-footpaths LV = 450mm 11KV = 600mm 33KV = 750mm

Cables in agricultural land LV = 1000mm 11KV = 1000mm (33KV = 1000mm to top of tile + 75mm below tile to duct)

Cables laid accross roads and along roads LV = 750mm 11KV = 750mm 33KV = 750m

All measurments are to the top of the duct unless otherwise stated.

If it was less than 450mm i would be arguing the point


I did come accross someone who was knocking a fence spike in the very edge of their property boundry and went straight through an 11KV cable. They heard a thump and the lights went out for about 2000 people!! Lucky for them the protection functioned and there were no injuries. They did go very pale when they were told it was ll KV which is funny as it sounds worse than LV. But if you are going to hit one go for the HV as the protection operates a lot faster than a 400A fuse in a sub station. The further you are from the sub the longer the fuse will take to operate and the worse injuries will result.

Moral to this is always use plans and cat cable dig by hand to confirm position etc.

 

[malcolmsanford]

True about that but even the DNO don't know where half there cables run. or more to the point what kind of condition there are in.

In our regulated world yes all new installations are buried so deep and need to be that deep, but we are talking of cables 50, 60 years old.

My brothers neighbour Slough way got a knock on the door a few years back from the local DNO saying they think the streets main cable come through his property, when they got round the back and confirmed it, it was about 3 inches below his damp course and for years he though it was an old imperial waste pipe. It ran the entire length of his house and then into next doors

 

[IQ Electrical]

True about that but even the DNO don't know where half there cables run. or more to the point what kind of condition there are in.

In our regulated world yes all new installations are buried so deep and need to be that deep, but we are talking of cables 50, 60 years old.

My brothers neighbour Slough way got a knock on the door a few years back from the local DNO saying they think the streets main cable come through his property, when they got round the back and confirmed it, it was about 3 inches below his damp course and for years he though it was an old imperial waste pipe. It ran the entire length of his house and then into next doors

Maybe he can charge them rent as the farmers do for underground/pylon installations!

 

[malcolmsanford]

Lol that's a point. Not exactly sure how this ended, but I think once the SEEB, which it was then saw this, they changed the route of the cable pretty sharpish.

 

[telectrix]

If the cable was actually at a depth of 200mm and not protected/identified then I'd be arguing the ---- with the DNO.

As Engineer54 has stated, if the area is a domestic garden then it is reasonable to expect the ground to be disturbed by digging etc. and with this in mind, I would argue that the DNO had a duty of care which obviously wasn't exercised!

I'd also be making a bit of noise on the fact that your friend has actually had a near miss as far as health & safety is concerned!

spot on IQ. i once drilled through a DNO incomer. as it was in a location where it was not expected to be, the DNO accepted responsibility for the repair. buggers would'nt replace my 16mm x 450mm masonry bit though

 

[rryles]

I've got some builders excavating some foundations at the moment. There are LV cables and gas pipes in the area, so they are having to do much of it by hand. These will be about 50 years old, so it will be interesting to see how deep they are. The founds are 900mm deep, so I'm sure we will uncover them.

 

[glasgowbiker42]

All good and correct information. Unfortunately,
thirty odd years in the trade has taught me that the regional electicity companies i.e. Scottish power etc sometimes make it up as they go along. I've seen some shockers over the years (pardon the pun)

 

[Engineer54]

latest cable depth spec from CN is

cables in footpaths or road-footpaths LV = 450mm 11KV = 600mm 33KV = 750mm

Cables in agricultural land LV = 1000mm 11KV = 1000mm (33KV = 1000mm to top of tile + 75mm below tile to duct)

Cables laid accross roads and along roads LV = 750mm 11KV = 750mm 33KV = 750m

All measurments are to the top of the duct unless otherwise stated.

If it was less than 450mm i would be arguing the point


I did come accross someone who was knocking a fence spike in the very edge of their property boundry and went straight through an 11KV cable. They heard a thump and the lights went out for about 2000 people!! Lucky for them the protection functioned and there were no injuries. They did go very pale when they were told it was ll KV which is funny as it sounds worse than LV. But if you are going to hit one go for the HV as the protection operates a lot faster than a 400A fuse in a sub station. The further you are from the sub the longer the fuse will take to operate and the worse injuries will result.

Moral to this is always use plans and cat cable dig by hand to confirm position etc.

Have you an official link for these cable trench depths?? The MV/HV depths are pretty much standard but those for LV are not standard at all. Over 700mm and your into derating territory. The 450mm are just not deep enough to be at a safe depth, unless run in ducts...

As far as i'm aware, all new road crossings are now to be only allowed in ducts, there also supposed to be providing spare ducts for any future requirements. If i remember rightly, the ducts are to be a min of 100mm.

 

[mechelec]

As stated in the post All measurments are to the top of the duct unless otherwise stated. This implies that all cables are to be laid in ducts.
As the cables are laid in ducts derating has to be applied regardless of depth. This is carried out at the design stage, it does not mean that the cables canot be buried at the specified depth.
As far as I know road crossings have always been ducted (there are exceptions) and as you say spares laid for future use.
I have not got a link to post but all figures were taken from the latest spec.