Regulations regarding a buried spur to power garage?

[PrenticeBoyofDerry]

Prentice - no offence meant but as I said I've seen people who clearly know nothing dispensing advice with utmost authority, which IMO is really dangerous. People who take the "I did my house and nobody died" argument to mean that they are an expert So I merely meant to ask if you are an electrician, than to imply your advice was wrong!

No offence taken, it can be quite a minefield when trying to search for informed advice on the internet, and to answer your question above, I am a qualified, experienced, registered electrician.

And I have tried with the wisdom I have to steer you down the right path with regards to the installation you require, best practise would be to have a 600mm trench and duct laid to carry the cable, the cable selection and size would require to be calculated taking the method of installation, the load demand and any voltage drop related to distance and lighting.
I personally would not connect as a fuse spur, as this could effect circuits that are part of the main house and introduce power loss to number of circuits if a fault was to arise from the cable to and within the garage and any connected loads.
So I would install at the consumer unit on a non RCD protected way and protect the circuits at the garage via a locally installed garage consumer unit with RCD protection on that, this would involve notification for new circuits though.
If you did spur from an outlet in the house then I would suggest that you then introduced a two pole isolator, this could be a switch fused connection unit, but you will be limited to a load of 13A at the garage, but the isolator will allow you to disconnect the garage distribution and internal circuits for the rest of the house, if a fault should ever arise downstream of the spur.

 

[bernardgreen]

Private drive or public high way. one foot is not deep enough. You will not be able to have the warning tape one foot above the cable. Even two feet is a bit shallow when you consider future resurfacing of the road.

To take it as a spur is not a sensible idea. You could as has been said lose half you sockets and lights due to a fault in the garage.

You also might need to consider providing a means of acess to your house should the need arise to isolate the cable when work or damage occurs to the road and you are not at home. That will be included, if necessary, in the way leave you obtain from the estate management.

An informal arrangement ( as opposed to a formal and binding way leave ) may end if the estate management is taken over by another management company or adopted by the local council.

A cable under a narrow foot path that ran between house and garden was a legal nightmare when the house was sold because there was no wayleave in place.

 

[mfarrow]

GN1:
View media item 67014Text goes on to say 500mm, to be sure.

At 600mm I'd start thinking about hiring a trencher.

 

[clifford1]

would you ask a plumber to fix your roof?

Yes. Plumbers work with lead. Interior plumbers fix water pipes, exterior plumbers fix lead flashing and guttering.

 

[EFLImpudence]

I think the OP is feeling aggrieved because he is treating the work as a DIY job.

In my opinion it is not.

To complete it satisfactorily and safely without asking a question about every single component and principle involved requires previous knowledge.

In those immortal words "He doesn't know what he doesn't know".

 

[d000hg]

GN1:
View media item 67014Text goes on to say 500mm, to be sure.

At 600mm I'd start thinking about hiring a trencher.

Very neat, thanks. Is 240V considered high or low voltage?

I would love to use a micro-trencher which can cut a gap 2" wide... no digging and virtually no re-surfacing required. And would take about 30min. Digging that by hand sounds a nightmare.

I'm wondering about other options like a Mole but that's probably for a different forum section. And that would surely raise issues for the "warning line 1 foot above the cable" - is that a legal requirement?

 

[bernardgreen]

Is 240V considered high or low voltage?

240 volt is LOW votage,

 

[JohnW2]

Very neat, thanks. Is 240V considered high or low voltage?

Low Voltage.

I would love to use a micro-trencher which can cut a gap 2" wide... no digging and virtually no re-surfacing required. And would take about 30min. Digging that by hand sounds a nightmare.

How certain are you that there are no other drains/cables/pipes/whatever under there that a 'micro-trencher' could plough through?

Kind Regards, John

 

[d000hg]

How certain are you that there are no other drains/cables/pipes/whatever under there that a 'micro-trencher' could plough through?

Kind Regards, John

There theoretically could be one cable but definitely nothing else. We're on the edge of our development but we have one street light - it is not known currently if this has a powerline under our house (the main street with all the drains and street lights is on the other side of our house) or if it goes around the property.
I had assumed this would be buried very deep, which was one reason I was keen to be as shallow as possible, but I would have to try and find out.

With the requirement to lay a warning line a foot above the cable though, could I not safely dig 1 foot down and check for such things before taking a second pass - or can a warning line not be relied on?

I should be able to get a plan to check. Can cable detectors be used on cables this deep?

edit: I am looking through documents we got when buying the house which may show such stuff. I'll update shortly.

 

[d000hg]

Untitled

• d000hg
• 18 Mar 2014
• 1

THis is from searches when buying the place. Our house and garage highlighted in red, behind us is a retaining wall to the rear of houses on a different, much older street.
It doesn't show electricity but does show how water pipes are laid up the main street as you'd expect. I'm certain mains electricity and gas is the same, the one wrinkle is the streetlight marked in orange.... does it have a cable under the houses or going round them, which our proposed trench would cross.

 

[JohnW2]

There theoretically could be one cable ... one street light ... I had assumed this would be buried very deep, which was one reason I was keen to be as shallow as possible, but I would have to try and find out.

The guidelines regarding the depth of any cable for the street light would be no different from those applying to your proposed cable - so that would definitely not be a safe assumption.

With the requirement to lay a warning line a foot above the cable though, could I not safely dig 1 foot down and check for such things before taking a second pass - or can a warning line not be relied on?

That's why I asked. If one digs by hand, one stands a chance of finding a warning tape, or even the cable itself, before damaging it - whereas a 'micro-trencher' would just chop straight through tape, cable and anything else down there. Whilst there should be warning tapes etc., you obviously can't be certain that they will have been installed, so you couldn't totally rely on the absence of a tape to 'prove' that there was no cable or pipe.

I should be able to get a plan to check. Can cable detectors be used on cables this deep?

You're talking about pretty sophisticated and expensive kit - and, I would imagine, far from 100% reliable.

Kind Regards, John

 

[d000hg]

Thanks John. methinks I need to chase a plan. Is that something that's public domain, or would it be exclusively owned by the property management company - and are they obliged to show it?

 

[JohnW2]

It doesn't show electricity but does show how water pipes are laid up the main street as you'd expect. I'm certain mains electricity and gas is the same, the one wrinkle is the streetlight marked in orange.... does it have a cable under the houses or going round them, which our proposed trench would cross.

It seems pretty unlikely that the cable to the streetlight would go under the houses - so it would seem much more likely that it goes around your house - as you say, right across the path of your proposed trench!

Kind Regards, John

 

[JohnW2]

Thanks John. methinks I need to chase a plan. Is that something that's public domain, or would it be exclusively owned by the property management company - and are they obliged to show it?

I don't know the answer to those questions, but, even if you could get a plan, I don't think you could take it to be giving anything more than a general idea where the cable goes.

Kind Regards, John

 

[Taylortwocities]

Utility companies have access to plans of services.
These show where 'known' services are located and their depths.

Even armed with these, working gangs will always use a scanner as a GUIDE before they get the digger started. The scanner might determine if anyone (like you) may have laid in a cowboy service, but its not a 100% test.

You can hire them by the day, but you'll need to know how to use it.
for example http://www.hss.com/g/49514/Detector.html