For help, advice and discussion about stuff not related to aviation. Play nice: no religion, no politics and no axe grinding please.
User avatar
By rikur_
FLYER Club Member  FLYER Club Member
#1896088
I'm starting to plan for getting a car charger installed.
The ideal location would be on the garage wall next to the drive.
The garage has a 4mm armoured cable from the main consumer unit currently fused at 32A.
The consumer unit is 35m away on the opposite side of the house.
Does the charger need to be connect to the main consumer unit, or could it use the garage supply?
(I think chargers are normally 7kW, so it would pretty much max out the 4mm cable).
If it could reuse the existing garage connection, would it desirable anyway to run a new cable? (thinking that over 35m on 7kW the voltage drop is likely to be material and it may be worth using an overrated cable to save on transmission losses).
Experiences welcomed.
User avatar
By stevelup
FLYER Club Member  FLYER Club Member
#1896089
Unfortunately, your 35M run of 4mm is not adequate. It wasn't adequate for what you already had it run for...

When was it done? Can you get them to come back and do it properly? Wonder why the used an undersized cable...

You're good for about 25A there - one option would be to program the charger to the lower current rating.
User avatar
By stevelup
FLYER Club Member  FLYER Club Member
#1896092
rikur_ wrote:Does the charger need to be connect to the main consumer unit, or could it use the garage supply?


Ideally, it doesn't touch your main consumer unit. You'd split the tails directly after the meter and fit a switch fuse there to feed the EV circuit.
User avatar
By rikur_
FLYER Club Member  FLYER Club Member
#1896100
stevelup wrote:When was it done? Can you get them to come back and do it properly? Wonder why the used an undersized cable...

New build 1995. I suspect the existing SWA might be a bit shorter than 35m (probably about 26m), as it runs directly under the house, which isn't an option for a new cable.
By Bill McCarthy
#1896103
Are you sure the existing cable doesn’t run through an alkathene pipe ?
Consider a pneumatic mole contractor to run new conduit.
User avatar
By rikur_
FLYER Club Member  FLYER Club Member
#1896113
Bill McCarthy wrote:Are you sure the existing cable doesn’t run through an alkathene pipe ?

Through the house it just lays loose on the concrete raft below the floor. Through the garden it appears to be just buried.
Consider a pneumatic mole contractor to run new conduit.
I've used these elsewhere successfully - unfortunately our house was built on land raised by 4ft out of floodplain by dumping a load of bricks and then adding a layer of top soil - makes any excavation hard work!
User avatar
By rikur_
FLYER Club Member  FLYER Club Member
#1896116
stevelup wrote:Just to put some numbers on my statements.

Max allowable voltage drop is 11.5V

27A at 35M of 4mm SWA is 11.3V.


Which iswhy I was thinking of putting in an overrated cable anyway.....
I *think* electric cars are ~ 40kWhr per 100 mile ...... so 4000kWhr per year of charging, double that when both cars are electric.

11.5v voltage drop is 5%, so implies 200kWhr ......

assume 20p per kWhr = £40 per year wasted on the cable (I think).
By rdfb
FLYER Club Member  FLYER Club Member
#1896138
I get about 4-4.5 miles per kWh. So a bit more efficient than your estimate. That's town driving. I suspect motorway driving will be closer to your estimate.

We have a 32A charger connected to the consumer unit using some kind of armoured cable - about 10m. If you have single phase 100A coming in (which is typical in the UK), then you can't realistically have much more than that for car charging without running out of power when everything is on. That might be a consideration if you expect to be able to charge two cars at once. 32A car charging at home is pretty good though - just a few hours to have more than enough charge for a day's typical use. It's possible today (with some hassle) to set up two chargers to maximise charge rate when possible but not use more than 32A between them. In the future that'll probably get easier.

More of a pain was the earthing. Car chargers are required to have a "proper" earth or equivalent*. There are some fault protection devices that can provide an equivalent and some chargers have them built in but they are rumoured to be noisy (they hum). Maybe not important for your garage, but in my case the consumer unit is under the stairs so I had them put in a proper earth rod which is used only for the car charger.

* which I find remarkable because it's to protect against a "PEN" fault where your car body might electrocute you but this kind of fault would also kill a child playing barefeet with the outside water tap on a hot summer day which seems a more likely scenario to me. But outside water taps do not require this kind of protection under the regulations!
User avatar
By rikur_
FLYER Club Member  FLYER Club Member
#1896143
rdfb wrote:More of a pain was the earthing. Car chargers are required to have a "proper" earth or equivalent*. There are some fault protection devices that can provide an equivalent and some chargers have them built in but they are rumoured to be noisy (they hum). Maybe not important for your garage, but in my case the consumer unit is under the stairs so I had them put in a proper earth rod which is used only for the car charger.

Ah - fortunately I have an earthing rod. (Before our house was built our garage was built as the site office for the development, running off a generator with an earthing rod. We have to be careful as we now have two earths - the supply earth which is in use, and earth rod earth which is just wrapped in tape near the meter.)
User avatar
By rikur_
FLYER Club Member  FLYER Club Member
#1896152
If it wasn't for the standing charges, getting a new 3 phase connection and going for a 22kW charger would probably be easiest. Just a short new cable from the pavement to the garage for a 3 phase supply (substation is opposite the house and probably easier to get to than our meter/consumer unit!!).
User avatar
By HedgeSparrow
#1896155
I complained to my energy supplier (Good Energy) that they've just put the Economy 7 rate up by an extra 150% (yeah, 2½ times what it used to be). I know gas prices are high and this reflects onto electricity prices, a hike like that is a lot. They told me that it's because Economy 7 is so popular now due to a high proportion of their customers charging their e-vehicles overnight. Huh!

Disgruntled I am.
User avatar
By Flyin'Dutch'
FLYER Club Member  FLYER Club Member
#1896171
HedgeSparrow wrote:I complained to my energy supplier (Good Energy) that they've just put the Economy 7 rate up by an extra 150% (yeah, 2½ times what it used to be). I know gas prices are high and this reflects onto electricity prices, a hike like that is a lot. They told me that it's because Economy 7 is so popular now due to a high proportion of their customers charging their e-vehicles overnight. Huh!

Disgruntled I am.


Can you imagine how disgruntled I am, we can get cheaper leccy for heating and ground and air source heating but NOT for charging your car!

@stevelup - see, so much to be grumpy about! :D
Colonel Panic liked this
By Cole Burner
#1896192
Don't delay if you want to/can claim the £350 OZEV grant - scheme ends at the end of March.
Just had a "Sync EV" socket installed, so far so good and very neat/compact.