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Is my power supply acceptable?

Discussion in 'The UK and Ireland' started by WannabeOwner, Sep 19, 2016.

  1. WannabeOwner

    WannabeOwner Member

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    United Kingdom
    Hoping there might be a Sarky here who could give me some advice.

    A few years ago our meter was moved. Turned out that we had a 4-core supply cable, with two wires shorted for each of Live and Neutral (to spread the load, rather than originally having installed a fatter cable, I presume).

    At that time the fitter said he was not allowed to connect 4 wires, in the original way, any more, so he connected just two of them and two cores were left no-longer-used.

    I had my Sparky run a before/after voltage-drop test with 3x 3KW fan heaters running, and he said the voltage drop (after the meter was moved) was significant (I've got the figures somewhere)

    I told UK Power and they said if we could provide a suitable load they would put logging on the line, and if the voltage drop was unacceptable they would replace the cable (at their expensive, as I understood it) but, no, sorry they do not provide any form of test load whatsoever /... funny that!!

    We have 5,000 Litres of hot water accumulator with 2x immersion heaters (19kW each, or something like that - if we ever needed to use them we would have to pretty much turn everything off in the house) so I figured to use them for a voltage-drop test. Long story short, at the time of the meter being moved the accumulator tank was being moved and the immersions heaters got lost in the process and have not therefore been fitted :( and therefore I have never had the opportunity to make a proper test

    On Friday night the cable up the pole (it is underground from house-to-pole) blew up - rain and wind got into some weakness in the cable at the top of the pole. We had had flickering lights all day, so presume that was "some water" getting in, followed by "enough water" to create a proper short.

    Linesman that fixed it said the cable was inadequate for a property of our size ...

    ... so I thought I'd check the Tesla logs for charging voltage, on the assumption that it is providing a "heavy load" when charging. They are showing around 235-237V when charging which, AFAIK, is within spec? (230V +10% -6%). So either Tesla is not a "big load" when charging, or I don't have a problem with voltage drop?

    I have a dedicated tethered cable which I use to charge (sorry, very non-technical explanation of "I have no idea what sort of charger I have"!!), I also have a type-2 connector (which I have never used, it was intended for guest EVs to charge), but I suspect that is on the same circuit so wont provide any more/different load, so only mentioning it "just in case".

    Any advice on whether I need to get the supply cable to the house upgraded, and if I should expect UK Power to pay, or not, would be appreciated. Many thanks for your help
     
  2. arg

    arg Member

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    That original setup does sound rather non-standard, though not necessarily wrong. But if the meter was moved, surely that was a new cable? or was it just moved a very short distance?

    The Tesla is a large load - perhaps 1/3 of your total available supply capacity - so should be sufficient to estimate the total voltage drop. However, you need to look at the 'before' and 'after' voltage. 235V while charging suggests you don't have a desperate problem with voltage drop, but doesn't tell the full story as maybe the no-load voltage has been set very high to compensate. If you look at the difference between the voltage that the Tesla shows when it is not charging and when it is charging at 32A, then multiply that by 3, you get the voltage drop you would have if you were taking 96A (ie. pretty much your entire supply capacity if you have a 100A supply). That in fact is slightly overstating the drop, as part of it is down to the chargepoint wiring (which isn't shared with other circuits in the house that might draw the rest of the load), but if that back-of-envelope calculation suggests all is OK then you have little to worry about.

    If the voltage is say 250V with the car not charging and it goes down to 235V when you start charging, then there may be an issue wanting further investigation.

    However, voltage drop isn't your main concern. If the underground cable into your house is undersized it may overheat and in the worst case cause a fire.

    It shouldn't be like that. If you have both a tethered cable and a type2 socket, then either they should be on separate circuits so you can indeed use both at once, or else there should be something like a change-over switch to make sure you can only use one at a time or some other arrangement to share the power automatically (like a pair of Tesla WCs - but they only come tethered, so you obviously don't have those). A simple 32A circuit with two 32A chargepoints on the end of it is contrary to wiring regulations.


    I'm assuming here that I've understood correctly and it's the (buried) cable from the pole into your house that you are concerned about.

    This is quite a tricky situation. That cable is the property of UKPN and it's their responsibility to specify what size it needs to be to do the job. They have different rules from the wiring regulations that apply to the wiring you own from the meter onwards, so you or an independent electrician can't just look at it and say "this is wrong" with any authority - that just invites the response "we make the rules and our rules say it's OK". Voltage drop could be one argument to convince them there's a problem to look at, but voltage within limits doesn't guarantee that there is no problem (if the suspect cable is quite short then it could have only a moderate voltage drop even if seriously overloaded).

    Assuming you come to agreement that there is in fact a problem that needs to be fixed, there's the question of who pays for it. In general, they are responsible for maintaining your existing supply, but if you request an upgrade or change to the supply, you have to pay for it. On the face of it you originally had a 100A (or whatever) supply that was paid for as such when it was installed, so if the cable has deteriorated and become inadequate then it's their responsibility to replace it. On the other hand, they might possibly argue that when you had the supply moved it was downgraded to a lower capacity supply (because it would have been expensive to do the move while retaining the original capacity), and you are now requesting a (chargeable) upgrade to the capacity. If the supply fuse was downgraded at the time of the supply move, then that would support that line of argument.

    However, what you actually suspect has happened is that the installer at the time of the supply move made a mistake - and you now have a 100A fuse (implying a 100A supply) with a cable that's not adequate for the job. If you wait until it catches fire, then it's clearly their responsibility to fix it. If you want to fix it proactively, I predict long and tortuous negotiations with UKPN. And if you leave well alone, probably nothing will happen....
     
  3. WannabeOwner

    WannabeOwner Member

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    Yup. 100 yards or so from pole-to-house, they just made a joint in the lawn [i.e. two of the original 4 wires], near the house, and I provided a trench to the new meter location probably 10' from that location.

    Haven't looked closely here (not used the Type-2) but the one that the [same] Sparky installed at work has a change-over switch. They could only fit one cable in the existing duct at work, hence the switch, so I suspect there are two separate runs here - but I'll check, thanks. Its only 10' from distribution board to the outside wall's charging point, so wouldn't have been hard to run two cables.

    Useful background about how to structure my negotiations (or wait for an underground fire!!), thanks for that.

    The protracted process of the Meter Move was rubbish (you probably know all this already ...). We had to fill in a form, with questions about the size of our supply etc - which we, as laymen, could not possibly know and I would contend their records should answer for them (excepting for a new supply request).

    Having done the paperwork they sent someone out for a site survey. He had adequate opportunity to spot the dual-wires coming into the old meter, I've got a photo somewhere ... I'll dig it out. The first we knew that there was a problem was when their fitters came to do the job. The delay getting them on site had been substantial and we could not afford another delay, so I was between rock-and-hard-place on asking for a better solution. So I took it up with the manager afterwards (and he said "If you prove there is a voltage drop we will replace the cable" ... that was some years ago, so no doubt someone, now, would claim that Black-is-White).

    Per chance Sparky was here today and suggested I put the Induction Hob and both ovens on, for a bigger load, and see what the Tesla Charging Voltage looks like then. Easy enough to try, dunno whether your point about those circuits not being part of the chargepoint wiring means that the test is not going to be useful. I was looking at the TeslaLog data for the voltage, which only shows when charging, so I'll wait until Wifee is home this evening and plug in for a non-charging check too.

    ElectricMeter.jpg
    Original Meter - not hard for the Surveyor to see a pair of Lives and Neutrals!! ... clearly 100A at that time but I don't know what the current limit is. Reasonably sure it is still 100A

    NewMeterLocation.jpg

    New location of the meter, and the hole-in-the-ground where it was spliced to the original cable.
     
  4. arg

    arg Member

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    OK, so if you've got a modern and adequate cable actually coming in to the house and it's just the section under the lawn that's suspect, then that's much less worry about the potential consequences if it goes wrong (and a stronger argument that it's their problem).


    They've got a legal obligation to tell you when you ask - but their record keeping is typically poor and pressing the point is likely to cause them to send someone out to take a look...
    http://www.legislation.gov.uk/uksi/2002/2665/regulation/28/made

    On the contrary, using just the car and scaling up slightly over-states the voltage drop, while using the car plus the other equipment gives you closer to the right answer (so long as you know how much load you've actually added).
     
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