DIY Doctor

A few questions on wiring practices

Postby peterh337 » Wed Jun 03, 2020 3:13 pm

Hi All :)

Background: electronics engineer, done tons of DIY electrics wiring including SWA stuff to outbuildings etc, and 3 phase many years ago

Q1: We have a single phase supply. The fuse used to be 80A. One day we got a letter from Seeboard offering to upgrade it for free. So we went for it. A man came and changed the fuse for a 100A one. Just like that. What size is the incoming cable? Is is about 20mm OD which might suggest 16mm2 rather than 25mm2. The distance is about 25m.

The reason I ask is because I am getting the house ready for 3 phase (for electric car charging, one day in the distant future) and then the meter will be relocated to a box on the outside of the house, and I will need to run a cable to the existing consumer unit. Fairly obviously 25mm2 will be OK but it is awfully hard to get this cable in place so smaller the better. That run would be about 3m. (Yes I know it would be better to use the existing incoming cable (which will be disconnected at the supply when the 3ph goes in) but it is buried deep under concrete).

Q2: Do UK Power Networks ever make any allowance on their 45cm duct depth and type requirement? On the phone they say absolutely never under any circumstances whatever, but they are rights jobsworths in their tone and would say that :) In the past this wasn't done and not far from me is a 33kV cable about 1ft deep in soft soil :) House supplies were often a few inches deep (in concrete).

I ask because we had a drive done in block paving. Under it is about 12" of concrete and at the bottom of that concrete is a 8cm duct (standard gutter pipe) which I got laid, all the way from the road, to our garage, in preparation for the 3ph supply. I didn't get around to checking the power company requirements for the house supply until the concrete was done... So it isn't 45cm deep but I don't see how the cable could be damaged, with a foot of concrete on top of it, and it being in an 8cm pipe.

We do have a Plan B which is to run the prescription duct through a garden, but it would be nice to use the one under the drive.

I would be looking for 3 x 80A or so.

Q3: Does the power company ever care about what is connected after the meter? They never used to. In a previous house I installed a big box with a load of 3 phase stuff (switch, RCDs, etc) and they were happy. It is possible they thought an electrician did it. Well, I tried to find one but as soon as I mentioned 3 phase and the location, they all wanted £500 per half day, so I did it myself.

I hear stories nowadays of electricians refusing to do any work in a house, beyond changing a bulb, unless the consumer unit etc is ripped out and replaced to comply with latest wiring regs, and wonder if the power company is similar.

Thank you for any feedback :)
peterh337
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Postby ericmark » Wed Jun 03, 2020 9:54 pm

In the main to get the grant for electric car supply you have no option but use a registered electrician.

The DNO can do what they want, they don't use same rule book as normal electricians.

There are rules on what is permitted from the HSE which are not found in BS7671.

The cost of a three phase supply can be huge, and there are EV charging units which measure house use and only allow car to use what is left, also some strict rules on earth type and RCD type, how ever much you want to DIY, it is really a non starter even for me as an electrician all my life.
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Postby peterh337 » Thu Jun 04, 2020 5:40 am

Thank you Eric.

I am trying to work out what your answer means relative to my questions.

It seems that the power company can change the rules. Is that correct?

The supply won't be cheap. Many years ago I paid 1k and I expect this would be several k.

I was never after a grant of any sort. That's news to me.
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Postby ericmark » Thu Jun 04, 2020 3:00 pm

I have tried in the past future proofing, it does not work, by time you come to use it, things have moved on.

You can't get the government help until you buy the car, and not all electric cars are the same, the two major problems are safety when using a TN-C-S supply (No problem with TT) and not overloading the supply fuse.

I know there is one with a special RCD protection and auto adjusting output, but since I am not intending to buy an electric car not noted what make, seem to remember called something like Zappi I am sure there will be others, but the idea is based around using current transformers, be it to use only solar power or not over load, but things are moving forward. To by time you get an electric car, there will likely be new ideas.
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Postby peterh337 » Fri Jun 05, 2020 11:29 am

These seem to be basically three charger types.

One is a 13A plug-in, which is OK for a little run-around which you are happy to charge all night. Actually I think that is the future of electric cars because the power isn't there on the average street by a long way to support distance commuting in Teslas.

Next needs a cooker-sized feed, which is possible in most houses, if not necessarily cheap due to the floorboards that may need to be lifted to lay the cable all the way from the consumer unit. This is OK on a single phase supply.

The top one is about 45kW and usually needs 3 phases.

What I am doing is laying the wires in place for the last one, but the same work would be involved for the middle one because in our house there is no practical way to lay say a 6mm2 flat cable where needed. So if I don't get 3ph connected I will just not use 2 of the wires. Not a big deal.
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Postby ericmark » Sat Jun 06, 2020 6:30 am

It's a new circuit, so needs notifying. Can't cheat as you need to use a registered installer for the car supply, and he will want to see paperwork.

Some way some how the charge unit needs to know how much power it can use, it may be wired, or it may be a radio link, until you know that you don't know what cable is required.

I have done it too many times, oh the floor boards are up, I will put in a cable for X then never used.

I did it with the fax machine, it needed with early machines to turn off the telephone to get a good baud rate so phone line went to fax machine, and then from fax machines to phones.

One fax replaced with email and internet, and two phones are nearly all now wireless, so all cables now redundant.

Son did same with central heating, LAN cable to each radiator for the TRV head, now all wireless, you can't buy a wired if you want one.

Just wait until you have selected car, then do it one time and right.
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Postby peterh337 » Sat Jun 06, 2020 1:42 pm

It is 100% legal to do your own installation, in your house.

Not sure what you mean by mandatory notification.

You need to use an electrician only if you want the grant, but that's worth only a few hundred quid at most and you will pay more than that extra in that situation.
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