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32A, 7.4kw Single phase charging installation cable thickness

sapkan

New Member
Nov 23, 2020
1
0
Bulgaria
Hi I am new to the forum and expecting delivery of a 2021 model 3 performance. It will be my first electric car so I am totally unfamiliar with charging and various electricity specifications. As far as I understand the mobile charger that the M3P ships with here in Europe can support single phase charging at 7.4kw from an industrial type socket. An optional adapter called blue commando is needed and is available directly from Tesla. Just checked the circuit breaker in my garage and it is 32A and the cable cross section of my installation is 4mm. I read somewhere (cant seem to find it now) that in order to charge at 7.4kw the cross section of the installation should be min 6mm. Can anyone confirm if this is the case or whether it is still possible to get 7.4kw charge rate with 4mm wiring.

thanks
 

jmaddr

Member
Mar 29, 2019
891
894
Florida
In the US, the thickness of the wire is regulated. I would assume it is on your side as well so you’ll have to check the Bulgarian and local regulations.
Higher current increases temperature on smaller gauges and when that happens the risk of igniting the cable itself or the connecting and surrounding components increases. For the US, wire is rated at maximum amperage but load should not exceed steady amperage of 80% of rated maximum. So if you want to support 32A for charging, which is a steady state load, you’ll need wire rated for 40A. Max amperage is always listed on the wire sheathing so check the writing om the side of your wire and see what it says. For the US, 40A usually requires 8 gauge (copper, other materials may be less) which is approximately 3.2mm but that does not include the sheath. If yours is 4mm for the wire, it looks like it should work...at least in the US. You’ll need to verify everything physically as well as check your local regulations. I’d consult a local electrician for sure.
 
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Sophias_dad

Supporting Member
Jul 29, 2018
1,045
950
Massachusetts
Be careful about what 4mm represents here. It looks like its not 'diameter' but rather area(4 square millimeters) of conductor. If it really is the latter, you can't move 7.4 kw across it safely, even at 240V. That doesn't explain the 32 amp breaker that's currently connected to it. If the 4mm is a real conductor >diameter< you should be okay. That's between AWG 6 and 8 in US terms.

You really need to talk to a local electrician, and at least in the US that wire and circuit breaker would have to be oversized by 25% because its a continuous load.
 

Rocky_H

Well-Known Member
Feb 19, 2015
6,108
7,099
Boise, ID
This question should be very straightforward to get an answer from there locally, but I don't think any of us here would know the electrical code requirements in Bulgaria well enough to provide that answer.

You have a circuit that will be supplying 32 amps continuous (or for long enough periods of time that it probably should be considered "long term" or continuous). What size of wire is required for that level of circuit? There should be a simple answer to that.

The only other difference I have heard of about this is that in the U.S., they have that 125% oversize for continuous load circuits, but I don't think most of European code does. For example, in the U.S., this 32A load would have to have a circuit sized for a 40A circuit. But in Europe, I have heard that they spec the wires and breakers for continuous loads already, so the 32A might just need to meet that 32A level--maybe 35A to have a normal round number.

What I would recommend here is that the Model 3 section of this forum won't have the right people seeing it to answer. You should ask this in the regional European section of this forum that includes Bulgaria. Because it's exactly the same question that would have been asked and answered already by people there with a Model S or X; it's not specific to the Model 3.
 

Schulmann

Member
Nov 27, 2020
25
26
Toronto
My fuse box is 100' away from my Tesla charger and I have a 8awg cable. For a full charge the voltage drops from 238V to 231V at the end. The cable is warm. I wish I had a 6awg installation. Cable lenght is very important too.
 

Cloggie

Member
Nov 18, 2020
105
46
West Midlands, UK
I recently had a charger installed, I am in the UK, and the electrician insisted on using 6 mm cable. Quite heavy duty compared to regular cable, but it will be safer and less resistance (heat and loss) than smaller gauge. The length of your cable is also an important consideration.

Please check with a reputable electrical installer in your area to make sure the installation is safe and adheres to local regulations.
 

TheRFMan

Member
Dec 15, 2019
389
298
Ottawa, Canada
My fuse box is 100' away from my Tesla charger and I have a 8awg cable. For a full charge the voltage drops from 238V to 231V at the end. The cable is warm. I wish I had a 6awg installation. Cable lenght is very important too.

At 32A, you're essentially dissipating 224W of heat in the wiring (7V *32A). Over a 100-foor length, that's not super high, but it's significant. I agree that over that length, 6 AWG would be better.

The resistance in the wiring is also making your charging less efficient. For every 7.4kWh of power sent to the car, you're losing 0.224kWh in heat, which is about 3% power loss in the cable.
 

Clivew

Member
Nov 19, 2019
218
347
Bedford, UK
I used 6mm cable for my Tesla Wallcharger, which is located 45ft away. Another charger that we have for another car, same distance away, which charges at 7kW is 4mm, and it does get warm.
 

zentage

Member
Dec 29, 2014
54
40
Norway
Norwegian electrician / Engineer here.
Can't speak for your country, but in mine theres no way we would secure a 4mm cable with a 32A circuit breaker. 20A max, especially when its for charging an electric car.

Charging electric cars is kinda the "worst" for cables as the load stay high over a long period of time (loads of hours) which can get that cable really warm and toasty if its not rated for the load.

If that cable (4mm) is going to be charging your car with 32Amps It will most likely get extremely hot and melt - causing a fire.

Call your local electrician and let them take a look at your installation.

Good luck!
 

Clivew

Member
Nov 19, 2019
218
347
Bedford, UK
Call your local electrician and let them take a look at your installation.

It was a certified electrician/chargepoint installer who fitted the original charge point!

I only found the issue recently when using this charger to top-up the model 3 and saw that the car was limiting the charging amps. I shall now replace with 6mm cable.
 

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