Cable size required?
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Sharpend
"It Just Is"
I never understand why people,if they have a spark coming or a spark as a mate, have to ask on a forum? Either there is no spark or not a very good one at that?
If the OP is in Wales, then this still falls under Part P, it is unchanged in Wales, and 3rd party sign off is not allowed in Wales, so, technically it is a breach of building regulations if someone signs off another's work, and also fraudulent.
Unfortunately there are a lot of EV charging "companies" out there who do not comply with the requirements of BS7671 nor do they follow the IET CoP.
Bearing in mind how long a car charger can run for, drawing a full 32A at the extreme end of the circuit, I am very surprised that @ 40m the VD is OK.
Also, the Joule heating and losses in the cable may be noticeable also, another reason to look back at cable sizing.
I doubt very much that there will be selectivity between the 32A breaker at the sub board and the supply breaker in the premises.
Also a 50A breaker in a domestic board...
I very much doubt that the board is rated at 50A for a single way, so it would need a seperate supply from the origin, then an RCD if the cable under the floor is not the correct distance from the external faces of the floor and wall.
Then there is...
Probably another doen things to think about.
I just hope everyone involved is well insured and can pass this off as compliant with 134.1 when it all goes wrong.
Max EFLI for a C or D50, which is probably the only way you will even get a hint of selectivity with a B32, and if you need a C32, then probably won't get it... 0.35 Ohms, good luck with that!
Unfortunately there are a lot of EV charging "companies" out there who do not comply with the requirements of BS7671 nor do they follow the IET CoP.
Bearing in mind how long a car charger can run for, drawing a full 32A at the extreme end of the circuit, I am very surprised that @ 40m the VD is OK.
Also, the Joule heating and losses in the cable may be noticeable also, another reason to look back at cable sizing.
I doubt very much that there will be selectivity between the 32A breaker at the sub board and the supply breaker in the premises.
Also a 50A breaker in a domestic board...
I very much doubt that the board is rated at 50A for a single way, so it would need a seperate supply from the origin, then an RCD if the cable under the floor is not the correct distance from the external faces of the floor and wall.
Then there is...
Probably another doen things to think about.
I just hope everyone involved is well insured and can pass this off as compliant with 134.1 when it all goes wrong.
Max EFLI for a C or D50, which is probably the only way you will even get a hint of selectivity with a B32, and if you need a C32, then probably won't get it... 0.35 Ohms, good luck with that!
Sharpend
"It Just Is"
@Sidewinder exactly what I had in mind, however as we don’t have a suitable authority to provide redress without some politically corrected reasoning then unfortunately this will continue until the fatality occurs again :C
Doc Hudson
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So does that mean you, (by your own definition not a spark), are signing part of a multi signature certificate? If you have managed to find someone gullible enough to sign for liability over your aspect of the job then personally I wouldn't trust them as far as I could spit. I am genuinely concerned you are being fobbed off about potential risks, dangers and liabilities of a project such as this. It would be very interesting, if you are willing, to see all of your design calculations for this extra load you are adding onto your house supply.
Doc H.
Doc Hudson
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Only just noticed this post, agree 100%! I could only see two realistic workable solutions for a supply of this type. (a) EV charger company does all of the work including supply back to DB and issues all certs etc upon completion of the job. or (b) EV charger company issues a specification for a supply to be made ready for their staff to connect onto, providing that a full EIC is available to confirm that the new supply is up to their specification before they energise their new charger.
Bottom line is that at the end of the day someone has to take legal responsibility if a property burns down or someone gets a fatal electric shock. Which when talking about these sort of loads can become a significant hazard if not designed correctly. On the news today I heard an article about Which promoting a campaign to reduce the number of dangerous electrical products in the home. https://campaigns.which.co.uk/product-safety/ There are an increased number of house fires caused by things like fridges, freezers, tumble Driers etc. and I will not be at all surprised if in 4 or 5 years we are not seeing a problem with complaints and failures due to dodgy cheapskate EV charging points causing fires and the like.
Doc H.
I am aware of a business about 10 miles from me ............... they sell and install car chargers ........... but out of the 2 employees, neither are sparks, so they have to use subbies , we can only speculate, but I suspect they get a fixed fee to do the install (a lot like lots of kitchen companies do) so compromises (or should I say cutting corners) are then the order of the day for the subbies to make any money.
Madness
AND they want to join a "scheme" so they can sign off the work?????????
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Obvious the OP is doing it himself, and has not the beginnings of a clue about how to size cables or what Zs or ADS is..
john..
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I am ignorant of many many things ( see wife for further details) BUT
what sort of current do these chargers draw? And how long are they usually drawing this for?
just curious
what sort of current do these chargers draw? And how long are they usually drawing this for?
just curious
I believe that there are two ranges, one that runs on a 16A commando, and the other that runs on a 32A, then you have the 3ph units, which go up to 32A 3ph I believe, I'm no expert either, and I've not read the IET CoP, not sure I'll bother.
However, I gather they run at full current for hours on end.
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Ooooh....I wouldn't want some weak of wrist ''5 dayer ' connecting one up for me!
I would imagine the majority of the charging would be done whilst the owner is all "tucked up for the night" as well
I can see a few meltdowns in the making.
Sharpend
"It Just Is"
It’s ok Kerch our boys in the LFB will soon makes amends by changing our regs.
If you want to wait a billion years you can do it on a 13a plug
But if you had a tesla model x then you would need more juice... a tesla super charger (in the US) is an eye watering 120kw 480v DC! It will recharge a 90kwh battery in under 70mins.
Domestic systems are anywhere between 3kw and 22kw three phase.
It's hard to tell (there must be a data sheet somewhere) but the domestic units are rated in RPH or range per hour and that would be dictated by the size of a cars battery and the charging circuitry of the car.
I will keep looking but cant find a data sheet that details the actual charging characteristics more just anti litigation nonsense.
L-ions usually start off low current then ramp up towards then end of the cycle but with the added electronics it can vary.
But if you had a tesla model x then you would need more juice... a tesla super charger (in the US) is an eye watering 120kw 480v DC! It will recharge a 90kwh battery in under 70mins.
Domestic systems are anywhere between 3kw and 22kw three phase.
It's hard to tell (there must be a data sheet somewhere) but the domestic units are rated in RPH or range per hour and that would be dictated by the size of a cars battery and the charging circuitry of the car.
I will keep looking but cant find a data sheet that details the actual charging characteristics more just anti litigation nonsense.
L-ions usually start off low current then ramp up towards then end of the cycle but with the added electronics it can vary.
a standard car charge point connector / lead is capable of 63a TP iirc. the car will take whatever power is available from the charge point (controller in chare point tells teh car what capacity is available), so if tis 16a SP the car will take 16a SP. if its 63a TP it will take 63a TP
SP chargers seem to come in 3KW & 7KW, then TP come in 22KW and higher. Mine will be 7KW SP so 32 amps. Furthermore it draws them constantly for four hours at a time, hence whilst my sparky was happy with 10mm (and so am I now) I was considering overrating it.
Sparky has now postponed due to flu so I've also had to postpone the installer and hence I'm stuck charging on good old 13A plug which takes 14 hours to fully charge.... hey ho.
Edit: DC chargers are also used commercially (at motorway services etc) which I believe use large lithium ion battery packs to provide very high charging power in short bursts. Tesla ones run at 120KW DC and there are now plans (EDF or EON I forget which) to put in 300KW DC chargers all over Europe!
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One other thing to remember, is that based on 32A for 4 hours 365 times a year, a 10mm sq cable at 20Deg C will cost you 60-62 kWh of electricity in losses.
This will increase above this though, because of the heating effect of the cable caused by these losses.
If you use a 16mm sq cable the losses based on 32A for 4 hours 365 times a year would be 38-39 kWh, again at a cable temperature of 20 deg C.
I don't have enough data on the install to correctly model the cable temperature, but bear in mind that energy will increase in cost, the current flowing through the cable will increase its temperature above 20 deg C, as its temperature rises the Joule heating losses rise, whilst 10mm sq is rated above what you are looking at current wise, look at the difference in cost of 10 - 16 mm sq now, look at the difference of 21 units of electricity now, annually and into the future, and see how much the payback would be on the larger cable.
Plus you will have a lower volt drop and EFLI.
Using an online "wholesaler" the 16mm works out £8 more expensive than the 10mm for 40m.
21 units @ what 15p/unit?
£3.15 so payback in < 3years for fitting the larger cable.
That's a very quick calc, and not looking at cable heating, so the payback may well be < 2 years.
Your spark should be working this out for you when it comes to large constant loads, else you need to find another spark.
This will increase above this though, because of the heating effect of the cable caused by these losses.
If you use a 16mm sq cable the losses based on 32A for 4 hours 365 times a year would be 38-39 kWh, again at a cable temperature of 20 deg C.
I don't have enough data on the install to correctly model the cable temperature, but bear in mind that energy will increase in cost, the current flowing through the cable will increase its temperature above 20 deg C, as its temperature rises the Joule heating losses rise, whilst 10mm sq is rated above what you are looking at current wise, look at the difference in cost of 10 - 16 mm sq now, look at the difference of 21 units of electricity now, annually and into the future, and see how much the payback would be on the larger cable.
Plus you will have a lower volt drop and EFLI.
Using an online "wholesaler" the 16mm works out £8 more expensive than the 10mm for 40m.
21 units @ what 15p/unit?
£3.15 so payback in < 3years for fitting the larger cable.
That's a very quick calc, and not looking at cable heating, so the payback may well be < 2 years.
Your spark should be working this out for you when it comes to large constant loads, else you need to find another spark.
All true I'm sure, but this would assume that I would fully empty the car's battery each day and thus need a fully charge every night. In reality I rarely take the car even down to 90% on an average day. Only now and then will I take it down to 50% and once in a blue baboon down close to zero. So being pessimistic the losses are probably a fifth of the amounts you're estimating. Nonetheless, you're right that this is probably the strongest argument to go up to 16mm I think.... hey ho.
Anywho, it's all laid at 10mm2 now!
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So your spark is not doing the whole job?
You are DIY'ing some of it.
Are you in England or Wales?
If you are in Wales, it is "technically" illegal and fraudulent for anyone to sign off the work of another under "Part P".
I think its abundantly clear that the OP isn't interested any anything constructive we have to offer................................. least of all doing the job properly, to the electrical regs and building regs..........
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