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Author: Subject: Garage fuse box rewiring for EV charger
Mr Whippy

posted on 20/1/21 at 02:38 PM Reply With Quote
Garage fuse box rewiring for EV charger

Hi,

I’m going to be getting an EV in the next couple of months and going to fit a 30amp charger to one of the garages walls. This garage is fed by a 60amp rated breaker in the house and the same rated breaker in the garages fuse box.

In the garage, there are two breakers in the fuse box each rated at 30amps. One is being used for two 58w florescent lights and two 20w LED outdoor flood lights so I think that’s just a messily 0.65Amps?

The other breaker is for one double 13A socket. So all combined that would be 13A + 13A + say 1 Amp for the lights so about 27amps max.

What I was wondering is can I just move the socket onto the same breaker as the lights and so now free a breaker for just the 30A car charger? Yeah that was quite a long winded simple question but I wanted to be clear…

Thanks

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cliftyhanger

posted on 20/1/21 at 03:08 PM Reply With Quote
Sounds like it needs a couple of changes first. What size cable is feeding the lights? for a 30A breaker it needs to be a ring OR a 4mm cable. The lights really should be fed off a 6A breaker. (the breaker is to protect the wiring and switches, I bet they are 10A light switches)

However, another solution.
The socket in your garage, can be fed off a single 4mm cable Or a 2.5 ring. Cut into that and use a fused connection box to feed your lights. Fit a 3A fuse, all is then good. If you only have a single (radial) 2.5 cable to the socket, best to fit a 25A breaker.

That will leave the other breaker free.
You need to be very aware of the earthing requirements. Have a dig about for what the regs are, they are there for good reason.

And the 60A supply to the garage, that needs to be 10mm cable. I hope it is.....

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BenB

posted on 20/1/21 at 03:30 PM Reply With Quote
60 amps to a shed- ye gods! What were they planning on?

Personally I'd put in a new compact CU. And probably go with the exterior lights either on its own RCD or fit RCBOs. Be a shame if an exterior light got wet and stopped the EV charging!

Agree re earthing requirements- do you know what you've currently got for the house?

How bad's the insurance? I recently looked at getting an eGolf. I was quite tempted until I found it was insurance group 20!!!

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David Jenkins

posted on 20/1/21 at 03:39 PM Reply With Quote
The man who installed my charger insisted that it had a circuit breaker of its own - it needs to be of a certain type (unsure why). The charger takes about 32A, so the circuit breaker is 40A, maybe 45A (I can't be bothered to go into the cold garage to check). The wiring upstream of the charger has to be rated to well above the rating of the circuit breaker.

The charger is wired as a separate spur from the consumer unit.

[Edited on 20/1/21 by David Jenkins]





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Mr Whippy

posted on 20/1/21 at 03:57 PM Reply With Quote
quote:
Originally posted by BenB
60 amps to a shed- ye gods! What were they planning on?

Personally I'd put in a new compact CU. And probably go with the exterior lights either on its own RCD or fit RCBOs. Be a shame if an exterior light got wet and stopped the EV charging!

Agree re earthing requirements- do you know what you've currently got for the house?

How bad's the insurance? I recently looked at getting an eGolf. I was quite tempted until I found it was insurance group 20!!!





This is a big 3 car garage so not a shed. It's got a beefy cable, going to the garage, can't mind what size it was as it was 15 years ago I fitted it. I'm happy enough to fit a larger fuse box, their not all that much cost, was just trying to use what I already have fitted... Garage is well earthed.

Good suggestions though and I'll look into whether it needs a special breaker and will fit a 6A one for the lights.

I checked the insurance, 2016 Nissan leaf 30kw Acenta - £27.61 a month (I'm £26.05 for the 2016 VW Up) so that's not too bad. Indeed the loan is just £40 more a month than the little up which should be negated by the cost of charging it and the reduction in service costs




[Edited on 20/1/21 by Mr Whippy]

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cliftyhanger

posted on 20/1/21 at 04:13 PM Reply With Quote
Worth remembering that you should only have one RCD in a system, unless they have different trip ratings (ie 30mA is std, but if you main CU has a 30mA RCD, the garage consumer unit should not have the same. Either no RCD in the garage, or use a 10mA type. Flippin expensive though)

You need to double check the charger rating. If it pulls more than 30A use a breaker that is bigger, then feed it off a fresh wire of appropriate size from the CU. Don't worry too much about the breakers adding up to more than 60A, as the whole lot will trip if you exceed that anyway, in your main house CU.

I would be inclined to get somebody to test the circuits once set up, make sure everything is in order. Too risky an environment to leave it unchecked. ie I have done some fault finding and remedial work where a DIY job from years ago wasn't checked in a rental. There was no continuity of earth, as the earth sleeving was in the connection. Easy mistake, and I was lucky. 3rd socket I check of 12.... Plenty of other honest mistakes too, but without a tester you just don't know.

And read the earthing regs! I have a suspicion it involves earth stakes.

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hobbsy

posted on 20/1/21 at 08:58 PM Reply With Quote
Re earth stakes I think it depends on the charger.

Myenergi zappi is one that doesn't need it I believe.

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daviep

posted on 21/1/21 at 12:30 PM Reply With Quote
quote:
Originally posted by hobbsy
Re earth stakes I think it depends on the charger.

Myenergi zappi is one that doesn't need it I believe.


Earthing requirement is the domain of the power supplier, I think technically you are meant to ask permission. If you google "exporting earth to garage" you can waste a few days of your life learning about whether you should "export" the earth from your house supply or isolate the garage and install a separate earth stake. It's more complicated than it seems.

Regards
Davie





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Mr Whippy

posted on 21/1/21 at 03:03 PM Reply With Quote
Hmm ok all things considered then, I think what I'll do is hire a mini digger and run a new cable to the garage wall. Then at least the charger can have its own fuse box and circuit.

Thanks for the advice.

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David Jenkins

posted on 21/1/21 at 03:44 PM Reply With Quote
quote:
Originally posted by daviep

Earthing requirement is the domain of the power supplier, I think technically you are meant to ask permission. If you google "exporting earth to garage" you can waste a few days of your life learning about whether you should "export" the earth from your house supply or isolate the garage and install a separate earth stake. It's more complicated than it seems.

Regards
Davie


I have been working with electrics of various kinds for maybe 50 years, including some high voltage stuff, but when it comes to domestic wiring I call in a local electrician. Costs me a bit, but when I see the equipment he uses to check on his installations I understand why. Earth leakage tests, other,tests for this that and everything else, plus it's remarkable the effort he has to do to keep up to date with the regulations. The best bit happens about 3 or 4 weeks later, when an installation certificate arrives in the post... keeps the insurance people happy, and counts if I ever decide to sell my house.

And, in reality, he's not that expensive when you work out his rate per hour. Especially as he can buy the cable and fittings far cheaper than I can, and he does pass those savings on in his bills.





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coyoteboy

posted on 21/1/21 at 04:57 PM Reply With Quote
quote:
Originally posted by David Jenkins
s rate per hour. Especially as he can buy the cable and fittings far cheaper than I can, and he does pass those savings on in his bills.


Only if you have a good one, and it can be an expensive trial and error process!

I'd fit a new CU and separate feeds if it were me. I have an 80A feed (exported earth, FWIW) into my single sectional garage, feeding a lighting circuit, a ring of 13A sockets, a spur for my PV input and a blank to run something large when i figure out what

I'd want that charger on its own, oversized feed for sure, you're looking at high currents and long durations while you're potentially not in the house. On the plus side, its better in the garage than in your house in terms of risk!


[Edited on 21/1/21 by coyoteboy]





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Benzine

posted on 21/1/21 at 05:33 PM Reply With Quote
quote:
Originally posted by Mr Whippy
Hi,

I’m going to be getting an EV in the next couple of months


Can't help with the question but wondered what EV you're going for? I'll be doing the same in April

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steve m

posted on 21/1/21 at 06:21 PM Reply With Quote
I may be reading the posts incorrectly, but i wasnt aware you could run a fuse box off another fuse box ?





Thats was probably spelt wrong, or had some grammer, that the "grammer police have to have a moan at




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Mr Whippy

posted on 21/1/21 at 07:16 PM Reply With Quote
quote:
Originally posted by Benzine
quote:
Originally posted by Mr Whippy
Hi,

I’m going to be getting an EV in the next couple of months


Can't help with the question but wondered what EV you're going for? I'll be doing the same in April


2016 Nssan leaf 30kwh, perfect for my needs. There's a lot of choices in EV now. If I had the cash I'd get a VW ID and if I was loaded I'd get a model 3.

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Mr Whippy

posted on 21/1/21 at 07:29 PM Reply With Quote
quote:
Originally posted by steve m
I may be reading the posts incorrectly, but i wasnt aware you could run a fuse box off another fuse box ?


Yip perfectly normal to do so

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cliftyhanger

posted on 21/1/21 at 08:06 PM Reply With Quote
Happens lots in rentals. Landlord has a fusebox, then off to a few in studio flats etc.
I know one bedsit place, the main fusebox feeds 11 bedsits, each with its own fuseboard, plus 3 electric showers, Madness, but apparently the main 100A fuse has never blown.

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hughpinder

posted on 22/1/21 at 04:54 PM Reply With Quote
You are supposed to ask permission from the Distribution Network Operator (DNO) to install heat pumps or EV charge points as they then assess your Earth an power supply and decide if it needs upgrading. I think this is actually free - certainly ENW was, but they just informed me my supply was ok (I have a 200A supply to my house). The point is not usually that one charger on its own is an issue, but if 10 people in a row of houses all want them then the whole supply cable may need upgrading.
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David Jenkins

posted on 22/1/21 at 07:47 PM Reply With Quote
quote:
Originally posted by Mr Whippy

2016 Nssan leaf 30kwh, perfect for my needs. There's a lot of choices in EV now. If I had the cash I'd get a VW ID and if I was loaded I'd get a model 3.


Good choice, if the range is sufficient for your needs. I had a 40kW Leaf, which suffered from the "rapidgate" problem - you can only rapid-charge the vehicle twice on a trip before charge rate is limited, as the battery doesn't have forced cooling. The lower-capacity batteries don't suffer with this problem.

The VW ID3 seems to have a lot of issues with software (immature and full of bugs, apparently) and Tesla owners are complaining about poor paint quality and poor panel fit (e.g. rain getting past the door seals in heavy rain).

For now I'll stick with my Kia Niro EV, a car that keeps winning lots of awards at the moment.





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craig1410

posted on 2/2/21 at 12:37 PM Reply With Quote
Hi,

I have recently installed a Wallbox Pulsar Plus 32A single phase charger. This is what I did:

Buried a SWA (armoured) cable of 3 x 10mm cores. The third core is used as an earth bonding conductor to safely export the house earth to the shed. The shed doesn't have any water pipes or gas pipes but itself is made of metal and has a steel H beam structure that is in contact with the ground. So it's really important that you have at least a 10mm bonding conductor as per the regs. The SWA armour is terminated into a brass gland at both ends with a banjo and is earthed at both ends to house and shed respectively. There is no RCD protection at the house end for the SWA and this is not required since it is armoured cable and will trip the MCB if the cable was chopped with a spade for example. However, you do need to do some calculations to check that the loop impedance is low enough to ensure the circuit will disconnect in the prescribed time (0.4s). My cable is only about 15m long so this was not an issue. I did calculations and later confirmed loop impedance by measurement as this is pretty important.

Installed a 63A MCB on a non-RCD spare way in the house consumer unit. This required me to combine two lighting circuits to free up a way, but I did some calculations on the number of lighting sockets being served by the two circuits and quite honestly there was no need for them to be separate. I think it was only done for convenience when an extension was installed. I still have two lighting circuits by the way so won't be plunged into complete darkness if one trips. We also have standing lamps around the house plugged into sockets so again not an issue if a circuit trips. I managed to source the exact same brand of MCB as was installed already and took a lot of care to get the best quality of connections at every stage because poor connections will cause heat and ultimately fire.

In the shed I installed a new Proteus CU with 100A main switch feeding 2 x 63A 30ma RCDs. I have 10 ways in total split as 5 + 5. It's important that you ensure that the RCD protecting your EV charger is a type A not the more common type AC because type AC RCDs can be confused by pulsed DC current and might not trip at all or certainly not at < 30mA as you would expect. So in my case I had to swap one of the RCDs over by buying a new type A unit. I'll probably sell the spare type AC on eBay to recoup some costs but if I was doing this all over again I would probably buy a slightly more expensive RCBO CU.

My CU currently has circuits for two ring final circuits of 32A each and a couple of lighting circuits at 6A each. And of course the EV charger at 40A. I'll probably add some more circuits over time but that's it for now.

The EV charger is fed by a 10mm twin and earth cable clipped direct to the shed wooden beams above head height. I could have got away with 6mm cable but the manufacturer of the EV charger specified 10mm so I went with that.

For testing, I bought a calibrated Megger MFT1552 on eBay and have used that to conduct all the various tests at each stage of the installation. This includes continuity tests, polarity, loop impedance (including Ze of the house supply) and insulation tests and RCD tests. I even bought the big blue book (the regs) and on-site guide and some other books to educate myself as best I could.

Re the earthing, I have installed a BEMT (Building Earth Marshalling Terminal) in the shed which is basically a metal connection block. This connects together the 10mm bonding conductor from the SWA cable and the shed CU earth and links these to the metal structure of the shed. For that I drilled and tapped a 6mm hole in the H beam and crimped on a lug to 10mm earth cable. I even installed a "safety earth - do not remove" label!

Further re earthing. If your installation has a TN-C-S (aka PME) earthing arrangement (very common) then you will need your EV charger to be protected against "PEN fault" which is where the neutral can become disconnected between your house and the supply causing the earth to essentially become live. If this happens and your car was charging and you touched the car then you could get a dangerous shock which would NOT be prevented by the RCD (I won't go into details but basically the RCD would be unable to detect the earth leakage and wouldn't trip). To guard against this you either need a charger with PEN fault detection built in (MyEnergi Zappi or Wallbox Pulsar Plus like mine) or you'll need a matt:e device (https://matt-e.co.uk) installed. These devices will detect the loss of neutral and disconnect all three conductors (Line, Neutral and CPC) within a specified amount of time (5s I think).

Another thing I learned is that, even if your DNO main fuse says 100A on the fuse carrier, this is no guarantee that there is a 100A fuse fitted. This simply tells you the maximum fuse capacity. It could be a 60A, 80A or 100A fuse inside. I actually have my DNO coming round today to pull the fuse and check what the rating is and if it's less than 100A I'm going to get it upgraded. There is a form you need to fill in to notify the DNO of your installation and part of that process is checking the fuse and service cables are up to spec. They also need to know about EV chargers to ensure they are upgrading their upstream infrastructure appropriately.

So there you go - I've no doubt I probably spent just about as much as I would have done if I had got an electrician to do the work but I've enjoyed the process and have learned along the way. I was intending to sell on my MFT once I had completed the job but it's a really useful bit of kit so I'll probably just keep it.

Lastly, there are a few excellent YouTube channels to watch if you want to learn more about electrics.

https://www.youtube.com/c/ArtisanelectricsUk
https://www.youtube.com/c/jjward
https://www.youtube.com/c/Thecjrshop

Update: DNO just been and gone and confirmed my fuse is 100A and service cables are all suitably rated so all good!

I hope this was useful but all above info is for entertainment purposes only and should not be taken as professional advice. If in doubt, get an electrician in.

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