Options for running outdoor cable to garden office

Hi there,

I'm having a garden office installed and it'll sit approximately 85m from the existing house. We want to run mains power to it and I'm struggling with how to get the cabling down the garden to it for the following reasons:

- Digging a trench: We have a fairly long narrow garden (approx 8m wide) and there are big (>15m) trees along both sides which I assume will have roots extending across into the garden making digging a trench along either side almost impossible. Digging down the middle *might* be possible but as you can imagine the Mrs is not keen to have a trench line down the middle of the lawn...

- Affixing the cable to the fence along one side: Unfortunately the fence is not what you'd call secure - it's quite old and very wobbly in some places. It's wood in parts but wire mesh in others. It's also our neighbour's responsibility to maintain so we can't rip it out and put a new one in (plus there'd be the cost, oh and did I mention the trees?). On the other side of the garden is a hedge so can't affix to that.

- Running a catenary wire through the trees and affixing the cable to that. I think this is do-able but I'm not sure how the catenary would be attached to the trees at either end and if it would damage the trees in the long term. Also, would it be possible to do this and have enough slack in the line for the trees to sway in the wind?

Is there another option I'm not thinking of? Could I run some sort of galvanised metal conduit along the bottom of the fence (or just off it along the ground) and peg it into the ground somehow? I'm thinking like the metal conduit you see in the basement of office buildings or car parks.

Thanks in advance for any suggestions!

Ben.

Steel wire armoured cable could be fixed to the bottom of the fence.

Your biggest problem is going to be the size of the cable.  For an 85 metre run (plus a bit more at each end, call it 100M) voltage drop is going to be an issue, forcing you to use a cable bigger than you might have first thought.

You can't fix anything to your neighbours fence ....

Are you a spark or DIY?

@ProDave Yup, am aware of cable requirements and have specced 10mm which should be enough to keep the v drop within tolerance for the loads I'll likely have on the line but ultimately this will be up to the spark who does the work. Would the SWA *have* to be fixed to the fence or could it be made secure in some other way?

@Murdoch I'm DIY but I'll get a spark to do most of the work. Just want to make sure I know what my options are in case whichever spark I choose hasn't done much outside work. I really just want to gauge how a spark would feel about some sort of metal conduit that's not attached to a fence but pegged/staked to the ground, if that would be safe and secure in their eyes. Good point about neighbours fence.

Thinqer77 said:

@Murdoch I'm DIY but I'll get a spark to do most of the work. Just want to make sure I know what my options are in case whichever spark I choose hasn't done much outside work. I really just want to gauge how a spark would feel about some sort of metal conduit that's not attached to a fence but pegged/staked to the ground, if that would be safe and secure in their eyes. Good point about neighbours fence.

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10.0mm down 85m+ of metal conduit????   

Why would you choose to use someone with little or no experience of the type of work you want doing??   :blink:

The best advice always has been..

Get at least three independent quotations for the proposed work..

Then make you decision based on the quotes you get..

If non are suitable then seek further quotes..

It sounds like this is going to need to be a new circuit back to the CU..

So you will most likely need someone to notify the Part p aspect as well.

:C

There are quite a few  problems there ,   as said , you shouldn't fix to some else,s  fence  , unless you had written permission I guess .    Trenching sounds like a nightmare .  

Two options left ;

1)  Trench down centre of lawn , lay a duct  & re turf. 

2)  You could erect some  poles to carry a catenary  wire .   Wire would only need to be at pedestrian access height .       

Thinqer77 said:

@Murdoch I'm DIY but I'll get a spark to do most of the work. 

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Budget about a grand minimum then you won't get any nasty surprises unless you over spec the garden office

there is much more to this than a cable calc

write a spec of what you want in the office then get 3 sparks to quote against it 

You'll probably be asked to help with the running the cable, so that'll save you a few quid.

If you're in Wales or England you need to comply with part P too. For insurance purposes make sure the spark gives an EIC for the work too

Thanks for all the sensible suggestions and I'm already on board with them. I'm fully aware this'll be a new circuit on the CU and will need to be Part P compliant, hence why I'm not doing it myself, I just want to be able to have an informed discussion with a sparky. Responding to some specific comments/questions raised:

@SPECIAL LOCATION What's the issue with 10mm for 85m? Is it a question of physically getting it into the conduit? I had assumed the conduit would slot or screw together in sections (a bit like you see in metal railings every now and again) so would only ever have to feed it through 1-2m of conduit at a time. I acknowledge that I'll be pulling a lot of cable through though! Regarding choosing someone with little or no experience, I misspoke a little there - I'm looking for advice so I can weed out those people when getting my 3 or 4 quotes...

@Evans Electric Would you suggest putting poles in rather than using trees? If so, is there a max distance that you can span with a catenary wire?

@Murdoch Thanks. When you say there's more to it than the cable calc, are you speaking about the whole job or just the selection of cable? Does my selection sound reasonable (i.e. 10mm for 85 or 100m. Load is likely to be on average 500-1000W with peaks of 3-5kW)

Has anyone seen any other type of ducting that could be laid along the ground (i.e. not under it) and not attached to the fence that would comply with BS7671 and a spark would be happy to sign off against?

Thanks in advance...

Thinqer77 said:

@Murdoch Thanks. 

Has anyone seen any other type of ducting that could be laid along the ground (i.e. not under it) and not attached to the fence that would comply with BS7671 and a spark would be happy to sign off against?

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The way you've written this suggests you are expecting a competent spark to come along and test, sign off and deal with the Part  P - good luck with that!

@Murdoch Noted but that's not quite what I intended, apologies. I'm trying to keep the costs down (who doesn't?) so would prefer to source the ducting and cable myself. I would of course expect the spark to inspect the materials before they're installed and if I can help with the installation (again to keep costs down) then I will. I just don't want to buy ducting that will never work (or be up to regs) and hence I came here hoping that asking the question of a wide range of experienced people might get me some suggestions of what will or won't work, or maybe come up with another clever solution I've not thought of. 

If a spark will never agree to me buying stuff beforehand then that's also useful to know - is that what you're saying? A spark will always want to supply the materials?

Thanks again for your patience!

Thinqer where in UK are you located 

Thinqer77 said:

If a spark will never agree to me buying stuff beforehand then that's also useful to know - is that what you're saying? A spark will always want to supply the materials?

Thanks again for your patience!

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you have to talk this through with the people who quote you, but most of us prefer to supply and fit .... that way the spark knows the source of all parts and then it’s down to them if there is an issue

i don’t have an issue with people supplying some of the accessories, but that’s where I normally draw the line. Also if people do supply lots of parts, I put my hourly rate up too ....

it’s really down to you to find a local reputable spark through recommendation ....

Thinqer77 said:

Would you suggest putting poles in rather than using trees? If so, is there a max distance that you can span with a catenary wire?

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No good ever came of attaching things to trees  ,  so I thought if there was  plenty of cover amongst the trees ,  plant some ....say ... washing line posts or similar , paint 'em green and string the catenary between them .    I'd have to just guess at how far between .   You 'd need something solid at each end  so you can wind the tension up on the wire  though . 

Don't even think of pushing 10mm cables down galvo conduit .    SWA is the way to go . 

Could the garden office be closer to the house?

H07RN pulled through ducting in a trench

https://www.plasticdrainage.co.uk/underground-drainage/polypipe-ducting/polypipe-ridgiduct-coils/orange-street-lighting-traffic-signal

Hire a mini digger, you'll have the trench dug up the middle of the garden in a day. It's a one time job, reseed the grass and the wife will get over it. 

Thinqer77 said:

@Murdoch Noted but that's not quite what I intended, apologies. I'm trying to keep the costs down (who doesn't?) so would prefer to source the ducting and cable myself. I would of course expect the spark to inspect the materials before they're installed and if I can help with the installation (again to keep costs down) then I will. I just don't want to buy ducting that will never work (or be up to regs) and hence I came here hoping that asking the question of a wide range of experienced people might get me some suggestions of what will or won't work, or maybe come up with another clever solution I've not thought of. 

If a spark will never agree to me buying stuff beforehand then that's also useful to know - is that what you're saying? A spark will always want to supply the materials?

Thanks again for your patience!

Click to expand...

I  think your logic of saving money on materials may be a bit flawed...

1/  Any electrician who has been running a business for any length of time will know full well that some materials are better quality than others..

e.g. some cheaper brands of cable may not have sheathing that strips easily...   Accessories may have poor quality termination screws...  etc..

So materials may be cheaper... but they take longer to install...

2/ Any electrician who has been running a business for any length of time will know full well that if they quote exorbitant material costs...

they may be less likely to get the job as 99% of prospective customers can get a broad idea about what the likely cost are by googling..

3/ Any electrician who has been running a business for any length of time, who has had customers supply their own materials,

will probably be familiar with the customer forgetting to get one or two significant parts that are essential and hold the job up whilst fetching the missing items..

4/ Any person purchasing materials for a one-off project is unlikely to be able to attract any bulk-trade discounts that would potentially allow better quality materials for a lower price.

Which is why the principle Murdoch mentioned...  to increase labour charges to cover any potential customer errors in the supply side...  is not uncommon.

If you are supplying yourself, I would suggest you get the spec agreed first with whoever is going to make it work safely in accordance with BS7671...

As It could get their backs up if you say "I was told this is OK off the internet"..

Guinness   

*************** AND  ************

while you are doing it DONT forget about internet and/or any security alarm cables as well!

Option 1.      Trench down centre of lawn, lay duct, and a spare, and water ( or another spare ) , install,cable, backfill, reseed ,tell wife to "deal with it"

option 2, if option 1 is unacceptable to present wife , tell her to sort it out

option 3.... see option 1

just saying 

:innocent

Thanks for all the helpful advice. Apologies for radio silence but the day job got in the way the last few days.

Agree with and understand all of the comments made (except perhaps the one about telling the wife to 'deal with it' - I may end up having to live in the office without electricity if I do that!)

@Badger I'm in SE9 (London)

@Murdoch Nope, can't move unit closer to house

@Murdoch and @SPECIAL LOCATION - great points and well made, thanks. I only have an interest in helping out where reasonable and useful to reduce cost if possible.

@kerching err, see above comments re matrimonial harmony. Nice shoes btw.

I think we've drifted from the original question a little though, which was basically is there any other way to get the cable down the garden without digging a trench? What would be a safe, secure and acceptable way to run the cable above ground (and preferably not through the trees)? Is there any way this can be done? What protection (above just using SWA) would be needed? Could some sort of outer metal case/conduit/box/whatever be pegged to the ground with the cable running inside? Could I install a secure baseboard to run parallel to my neighbours fence, say 10cm tall from the ground, suitably pegged etc so it's solid, and then cleat the cable along that?

Thanks for any suggestions!

Ben.

I'd ask your neighbour and just clip direct to the fence, it's easy to get hung up and overthink things, what about if x, y and z happens but in reality a cable run along the bottom of the fence isn't going to come to any harm, the main risk is if the fence is replaced but you'd be consulted on that before it happened anyway. 

If they refuse I think your baseboard idea is a good one.

I'd avoid any hanging from trees and installing poles to catenary wire it. For a run that long you're going to have some serious tension which means hefty poles, even with intermediary poles. The main thing is catenary wire/overhead cable runs just look like a dogs dinner, bear in mind you, and more importantly the mrs. is going to have to look at it for the next however many years. They have their place but in a nice garden isn't it.

The most important thing is what the spark who will be installing it thinks as no matter what you go with or try to push for if the spark isn't happy it won't be getting signed off.

Thinqer77 said:

Thanks for all the helpful advice. Apologies for radio silence but the day job got in the way the last few days.

Agree with and understand all of the comments made (except perhaps the one about telling the wife to 'deal with it' - I may end up having to live in the office without electricity if I do that!)

@Badger I'm in SE9 (London)

@Murdoch Nope, can't move unit closer to house

@Murdoch and @SPECIAL LOCATION - great points and well made, thanks. I only have an interest in helping out where reasonable and useful to reduce cost if possible.

@kerching err, see above comments re matrimonial harmony. Nice shoes btw.

I think we've drifted from the original question a little though, which was basically is there any other way to get the cable down the garden without digging a trench? What would be a safe, secure and acceptable way to run the cable above ground (and preferably not through the trees)? Is there any way this can be done? What protection (above just using SWA) would be needed? Could some sort of outer metal case/conduit/box/whatever be pegged to the ground with the cable running inside? Could I install a secure baseboard to run parallel to my neighbours fence, say 10cm tall from the ground, suitably pegged etc so it's solid, and then cleat the cable along that?

Thanks for any suggestions!

Ben.

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In some locations it is not feasible or economically viable to dig trenches...

Basics to remember..  

SWA. (armoured cable),  is designed to be installed outdoors without any need for conduit.

Any boundary wall / fence  that is your own property is easy to manage and supervise if you choose to fix anything to it..

(the only uncertainty is weather blowing it down).

Any boundary wall / fence that is owned by a neighbour is basically 100% impossible to predict if it will still be there next week!

There is nothing stopping you from constructing anything to fix a cable to...

e.g.  wood battens / decking boards, etc.. spiked into the ground, running the length of the garden suitably concealed behind the flower bed!!

I have done this before, (not in mid summer when all plants & flowers are in full bloom)..

You get to the balance between something looking a mess running up the garden -vs-

Suitably concealed low level around a perimeter, where it is unlikely to be damaged.

An armoured cabled fixed to such a structure is unlikely to be accidentally damaged buy digging as it is visible above ground!

opcorn