Advice on EV charging catenary wire.

Question

Hello, 
 I don't know if this is the right place for this query but here goes. 
 I have a slightly unusual, (or perhaps not so unusual to you guys), question with regard to a predicament I find myself in. 
 My son's work wants to provide him with an Electric Vehicle. 
 We live in a ground floor flat in a block of four and we each have our own garden at the rear of the block. D irectly at the rear with a pavement on one side consisting of 3 x 2 slabs laid sideways on. There's a small/narrow single dead-end access road. Which has a couple of street lights and is the property of the local authority. The road is used by all the flat occupants and there's parking at the dead-end. 
 Around six vehicles use the road including a large Ford Transit van of the neighbours. There's been a skip lorry come up the back road dropping skips once or twice over the years. The lorry just fits the width of the road with 6 inches to spare either side. That's about as big as could get down the road as thee is a very tight bend around the garden ends as the road approaches the rear of the flats. 
 When the road was laid, the council graciously put in a drop kerb entrance to our garden for the original owners some 50 years ago. O ne other flat has the same arrangement and we both have an entrance to a small driveway. Our driveway is just wide enough to open the car doors and we have a wooden ship lap garage with green mineral felted roof directly behind the small driveway. The garage stretches 16ft back to the end of our back garden. The cars never been in the garage since we had it built! Its got a bench with a vice, as all good garages should have and just about everything else under the Sun in it. 
 The distance from our ground floor flat in a straight line to the slightly diagonal end of the garage nearest the house is around 30m. 
 The road has a gas main running through it and a major drainage pipe for the street of 40 houses too. 
 From what I have read, a Catenary wire must be no lower than 5.8m in height above a road? 
 The neighbour upstairs would never let us attach any anchor or cable to her wall. That's another story... 
 We have a small area outside our back door that belongs to us around 3m x 2m. 
 Could a Catenary wire be run from say, the top of a 21ft scaffold tube, (As suggested by a scaffolder I know ), that would be concreted in the ground for a foot or so and fixed up against our wall and secured in a couple of places to the wall but the final bracket further up just short of the flats divisional split. Then the cable would run over the road and the same tube arrangement attached to the side of our garage and finally an EV charger fitted in the garage. 
 The tube would then reach up to the 5.8m height. The tube would not obstruct any windows or the like upstairs. 
 Is this the way to go or am I just being silly. Of course a qualified Electrician would be called in to do the job. I have a feeling he would not like the scaffold tube idea... 
 What is the best solution? 
 Any Help appreceiated, 
 Iain

ebee · Accepted Answer

Stewart, as well as BS7671 there may also be Building Regs/Planning issues too

Chris Pearson · Answer

Thank you - that makes the situation much clearer. You would have to pay an additional daily charge, but a separate supply to the garage might be possible. 
 Obviously, we are in the middle of an energy price crisis, but it was not long ago that one could get a supply with a low standing charge albeit at a higher unit charge. 
 If the company supplies the EV, will it pay for the leccy?

AJJewsbury · Answer

The distance from our ground floor flat in a straight line to the slightly diagonal end of the garage nearest the house is around 30m. 
 
 That's quite a span - 30m of typical EV cable (6mm&sup2;+data) will be well over 10kg (plus a bit for snow/ice loading) - which I suspect translates to quite a considerable horizontal force on the supports - especially as you'll likely have to tension the catenary to reduce sagging. If you poles are unsupported for their top 3m of so, that's quite a lever effect. Even scaffold poles will bend if the forces are high enough. You'd also need some means of access at height to put it all together - I doubt you'd be able to assemble it all and just hook it up at the ends from a ladder. 
 It's certainly possible to trench across public highways - not necessarily easy (permissions will be needed) or cheap (likely to need to use a LA approved contractor), but possible. 
 Alternatively send him out to do the shopping and let him charge at the rapid chargers in the supermarket car park! 
 - Andy.

ebee · Answer

Some of the cynics might be of the opinion. 
 Well although climate change is inevitable we are still capable of speeding/slowing it to a degree by our actions so we need to consider the maths first :- 
 1/ What does it cost to make the infrastructure (wind turbines, solar panels, wave generation etc) not only the direct cost in &pound;s but cost to the environment (global warming for one), end of life disposal etc. 
 2/ Those costs must be deducted from the savings made. Rose-tinted glasses must have no place here. 
 3/ What cost to civilisation as a whole and to people individuals will occur by changing our way of live (what difference will it make to the way we live and therefore the knock on effects). 
 
 I`m all for saving a shilling and saving the planet but I think interested parties don`t give us the whole picture. As Carla Lane (Bread - the TV programme starring the Boswells) might have written " It`s not a lie, it`s merely a different version of the truth!"

AJJewsbury · Answer

I thought that the cable would just be power from the house terminating at the EV Charging unit in the garage, then the data would just be in the standard 2-3m EV cable from there to the car. 
 
 There are a couple of signal wires in the flex between the charge point and the vehicle (to do things like check that it's plugged in at both ends before energising and negotiating charge rates), and that can be sufficient for a minimal install. The data alongside the main supply cable can be used for a number of different things - either for a simple current clamp on your incoming supply (so the charge point can reduce consumption or switch itself off, if it seems you're about to overload your supply - e.g. because you're cooking or have an instantaneous electric shower at the same time) or as a general Ethernet style connection to the internet so the charge point can get tariff data and so schedule charging for the cheapest times (or to timeshare capacity on the distribution network). There was a recent government diktat saying amongst other things that charge points should have access to the internet - but I can't remember the details and I'm not sure if it's come into force yet. 
 - Andy.

mapj1 · Answer

The tension in any wire is infinite if you pull it horizontal, so there has to be some droop - a wire under its own weight takes up a coshine curve, but as a first approximation, pretend it is a pair of triangles, with all the weight at the centre, and massless lengths that are straight. Then it solves as trig. (same formula as power factor...) 
 for 6mm2 wires without a tension core (steel) ~ 20m is as far as I would go, and that would be with a large-ish droop of about1m of droop. You need a lot of scaff pole in the ground as well, unless you cast it into several cubic feet of cement. There is a reason that the DNOs use most of a small tree per post. 
 It can be done, but if you go over the road or under it, you need the consent of the road owner - who owns the access road ? 
 It may actually be easier to get a pipe laid into the road and a couple of manholes on either side. 
 Agree, not easy. 
 Mike.

mapj1 · Answer

Maybe still worth the question to the council. Trenches are dug all the time in roads with gas mains, drains water pipes, telephones and god forbid electricity as well. Normally organized by depth not to collide. 
 e.g. 
 
 A gas main should normally be laid with a minimum depth of cover of 750 mm in a road or verge and 600 mm in a footpath. 
 A gas service pipe should normally be laid with a minimum depth of cover of 375 mm in private ground and 450 mm in footpaths and highways. 
 
 However, these depths are only a guide and should not be relied on when carrying out work near gas services or mains. gas pipes may have projections coming from them, such as valves, which are not shown on plans and may have less depth of cover than the pipe. 
 http://streetworks.org.uk/resources/publications/ 
 has some solid industry guidance 
 Until the ground is land-scaped, and then absolutely everything is at the wrong depth. 
 
 At leasr you then have a figure tho conjure with and justify not doing it right now. 
 . Mike

Advice on EV charging catenary wire.

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