Speak EV - Electric Car Forums banner

1 - 11 of 11 Posts

·
Registered
Joined
·
66 Posts
Discussion Starter #1
The CU in the house says it has a 32A breaker to the garage. Garage is detached and I estimate the run to be no more then 20m from house CU to garage CU.
Garage is physically half as far, but just compensating for the way the cable might run along the inside of the walls and underground.
In the garage there is a smaller CU with 2 breakers, 16A for the socket and 6A for the lights.
Using common sense, I would expect the cable to be capable of at least 32A because it is protected by the 32A breaker.
I am not sure whether I will be allowed to draw 32A in the garage to feed the EV charger (after disconnecting all other usages)
I dont mind if it drops to say 30A. At least I'll be getting more than the next available size of charger (16A).
I dont really want to put in a new cable because it will require additional £1000+ of trench work and there will be an ugly cable run on the outside wall.
Plus I cant imagine how one would route the new cable inside the walls to hide the cable, unless I spend even more money for an invisible job.
I'm mentally preparing to have to use the granny charger as my last resort.
Anyone had a similar dilemma?
 

·
Registered
Joined
·
16,858 Posts
It’s notifiable work and so you really need a qualified electrician to look at it. Also the standards have changed and I expect the original cable didn’t have a car charger in mind.
 

·
Registered
Joined
·
4,701 Posts
Using common sense, I would expect the cable to be capable of at least 32A because it is protected by the 32A breaker.
Probably.
But before going any further you need to determine what size it actually is.
If there is an exposed section somewhere you might be able to see embossed markings on the sheath which might include the core sizes, or a make and part number that could identify it.
Otherwise someone would need to disconnect an end and measure and count the strands in a core to work out what it is. Some electricians might be able to eyeball it.
 

·
Registered
Joined
·
390 Posts
If I use my SWA to my shed installed about 25 years ago as an example it’s embossed with ‘2 x 4’ denoting 2x4sqmm conductors (the sheath provides the earth in this case). A quick call to the manufacturer with vernier dimensions provided a confirmation. I don’t use this for charging.

Some cables have the manufacturer code and no conductor info and so can be looked up or a call made. Or, if safe to do so, a pic of the ends with something in shot for scale.

The embossing usually repeats regularly along the cable but can be hard to see as black on black so fingertip search followed by a close look is needed. Rubbing white chalk on helps.

If you are going to use an approved installer to access the grant they will want a bunch of photos (or much better a visit) anyway and will need to know your best guess of the route too as the ‘installation method’ affects the max continuous current rating quite dramatically (the best analogy is a rolled up vs straightened out extension lead and the resulting heat dissipation).

You may find a workable solution with one of the options that has configurable max current and a CT clamp to allow for other garage use at the same time.

You may need some CU reconfiguration if the garage supply shares an older RCD with stuff you care about in the house. Firstly for safety and secondly for nuisance trips and for fault finding later.

How you safely earth the garage after will depend on what charge point you choose. Personally I don’t subscribe to the ‘I will always charge it inside the garage’ idea as we all know that process gets annoying quickly and soon you get a second EV.
 

·
Registered
Joined
·
390 Posts
Just to add that it’s often easier and cheaper to take a new cable from the meter box via its own mini CU and leave all the existing as-is so I would also look at that. The sparks will still need to assess the house load.
 

·
Registered
Joined
·
508 Posts
The CU in the house says it has a 32A breaker to the garage. Garage is detached and I estimate the run to be no more then 20m from house CU to garage CU.
Garage is physically half as far, but just compensating for the way the cable might run along the inside of the walls and underground.
In the garage there is a smaller CU with 2 breakers, 16A for the socket and 6A for the lights.
Using common sense, I would expect the cable to be capable of at least 32A because it is protected by the 32A breaker.
OK - that's a fair assumption, so lets assume for a moment that cable to the garage is safe to draw the full 32A.

I am not sure whether I will be allowed to draw 32A in the garage to feed the EV charger (after disconnecting all other usages)
Will not be allowed unless you completely disconnect the power sockets and lights circuit from the Garage CU, which would not make sense for you to do.
I dont mind if it drops to say 30A. At least I'll be getting more than the next available size of charger (16A).
I dont really want to put in a new cable because it will require additional £1000+ of trench work and there will be an ugly cable run on the outside wall.
Plus I cant imagine how one would route the new cable inside the walls to hide the cable, unless I spend even more money for an invisible job.
I'm mentally preparing to have to use the granny charger as my last resort.
Anyone had a similar dilemma?
You could ask an electrician to drop the lights MCB to 3A and then install a 16A EV charger. An electrician may allow this given suitable calculation for diversity.

Otherwise, just run a new supply feed to the garage for a 32A EV Charger - example: a 10mm SWA/armoured cable.
 

·
Registered
Joined
·
763 Posts
The CU in the house says it has a 32A breaker to the garage. Garage is detached and I estimate the run to be no more then 20m from house CU to garage CU.
Garage is physically half as far, but just compensating for the way the cable might run along the inside of the walls and underground.
In the garage there is a smaller CU with 2 breakers, 16A for the socket and 6A for the lights.
Using common sense, I would expect the cable to be capable of at least 32A because it is protected by the 32A breaker.
I am not sure whether I will be allowed to draw 32A in the garage to feed the EV charger (after disconnecting all other usages)
I dont mind if it drops to say 30A. At least I'll be getting more than the next available size of charger (16A).
I dont really want to put in a new cable because it will require additional £1000+ of trench work and there will be an ugly cable run on the outside wall.
Plus I cant imagine how one would route the new cable inside the walls to hide the cable, unless I spend even more money for an invisible job.
I'm mentally preparing to have to use the granny charger as my last resort.
Anyone had a similar dilemma?
Yup sounds like a similar setup to here.

I just went for a 16A Chargemaster for simplicity as CU was in the middle of the house, garage feed had a 32A breaker but cable was armoured 2.5mm not 6mm+, with no easy access out. No doubt I could have raggled plasterboard etc to get the cable to an outside trench all the way around the house to the garage etc but could no be bothered.

As 1) 99.9% of all my charging was free rapids a short walk along the road. 2) although the rapids recently started charging, thanks to covid I'm now working from home permanently. If on an odd day I have to go into work I can either book a workplace charger or use the P&R there which is still free charging. So yeah no hurry to charge. Guess what I'm trying to say is it really depends on your circumstances.

My car is 16A anyway but if the car could take 32A ironically that would be more useful say in event of a long journey where a rapid is bust and I have to sit out a slow charger for a bit... This has happened so many times I've lost count.

Cheers
 

·
Registered
Joined
·
4,095 Posts
Just to add that it’s often easier and cheaper to take a new cable from the meter box via its own mini CU and leave all the existing as-is so I would also look at that. The sparks will still need to assess the house load.
I'd agree with this as well as all of the rest above. Don't compromise on less than 32A charging, and ideally build in capacity for 2 X 32 charge points as even if you intend to move it's likely to be wanted in the future.
Is your meter inside with your CU or external in a meter box? If the latter, how far is that from where you park your car?
 

·
Registered
Joined
·
66 Posts
Discussion Starter #9
Thanks for all the responses.

But before going any further you need to determine what size it actually is.
If there is an exposed section somewhere you might be able to see embossed markings on the sheath which might include the core sizes, or a make and part number that could identify it.
Fortunately the cable exits the floor into the garage CU and I can see some markings "BASEC ELECTRIC CABLE 600/1000V ALSTERMO 89 06". I could also see 2 conductors, one red other black, but couldn't see number of strands in each conductor. And There is an external green/yellow wire which goes out to an earth rod.
Do you think this is 6mm cable capable of 32A?

You may find a workable solution with one of the options that has configurable max current and a CT clamp to allow for other garage use at the same time.
I like the idea of a configurable output charger. That way I can limit the charge rate if ever I need to use the sockets after midnight (unlikely). More likely because the existing cable can’t do 32A.
I’m not sure if any of the OLEV compliant chargers can do this. Didn’t I read somewhere the chargers need Ethernet back to the router? I have a feeling I’m not going to get a smart charger.

I'd agree with this as well as all of the rest above. Don't compromise on less than 32A charging, and ideally build in capacity for 2 X 32 charge points as even if you intend to move it's likely to be wanted in the future.
Is your meter inside with your CU or external in a meter box? If the latter, how far is that from where you park your car?
Most likely the EV I get will have an 11KW OBC, hence the desire to at least be able to supply that.
If/When we end up with 2 EVs, the other charge point can be taken from the meter (outside) it would be nearer to where the other part of the drive is. But that will be many years in the future.

Otherwise, just run a new supply feed to the garage for a 32A EV Charger - example: a 10mm SWA/armoured cable.
I am trying to get a preview of whether the installer will insist on a new cable and hence trench so they can make some money for no reason.
If you guys think it should be able to do 32A, I would keep looking until I find an installer that is happy to use the existing cable.
 

·
Registered
Joined
·
390 Posts
The onboard nominal 11kW chargers are all 3 phase and will only function at the bog standard nominal 7kW/32amp on single phase so that’s a red herring unless you get 3 phase installed.
 

·
Registered
Joined
·
390 Posts
The issue with 4 versus 6sqmm is that the outside diameter of the swa is only different by a fraction of a mm and both usually use 7 strands.

Measuring one of the 7 with a caliper will do it but clearly needs some disconnection and fiddling.

I would just get someone to assess and quote.
 
1 - 11 of 11 Posts
Top