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Steve G.
Steve G., Electrical Engineer
Category: Electrical
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Experience:  27 years in Electrical Engineering, designing electrical plans and specifications.
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I installed a electrical vehicle charging station in my garage.

Resolved Question:

I installed a electrical vehicle charging station in my garage. It is L2, providing 6kW of power or 25A @240V. I used 50Ft of 10/3 alum flexible conduit with a 30A breakers. When in use, the conduit is very warm to the touch. 10 AWG is 1 ohm per ft, yielding 30W per line over 50ft. Is this connection underrated for the load? What should I have done. Thanks
Submitted: 1 year ago.
Category: Electrical
Expert:  Steve G. replied 1 year ago.

Hello there and welcome to Just Answer. My name is XXXXX XXXXX I will be assisting you today. I am an engineer with over 30 years of electrical and electronic training, repair and installation experience. I will try and answer your question accurately and precisely so that we can get you on your way.

Are your conductors copper or aluminum?

Please let me know so that we can continue.

Regards

Steve

Customer: replied 1 year ago.

solid copper

Expert:  Steve G. replied 1 year ago.

Ok, your #10 conductors in MC are good for 30A. 50 feet is not a long run either.

Do you actually have 240V at the equipment? Or maybe 230 or 220?

Can you check that?

Customer: replied 1 year ago.

Yes, I measured 240VAC RMS between phases with Fluke digital meter at the receptacle with no load. With load, I see about 237VAC


 

Expert:  Steve G. replied 1 year ago.

Ok, for continuous loads, the NEC requires that you breaker (and wiring) be rated 125% of the full load of the equipment. 25A x 1.25 is 31.25A.

Your breaker and wiring should be rated for 40A - the next common size up from 31.25

That would be to comply with code, however, when it boils down to it, #10 conductors are good for 25A so I'm not sure why they are warm for such a short run.

Are you sure that the load is 6KW?

Please let me know so that we can continue.

Regards

Steve

Customer: replied 1 year ago.

OK. I had 40A breaker originally but reduced it thinking 40A was too high.


 


I have a residential-type power meter in series with this load so I can watch power draw when charger is in use. From that I confirm 6kW, consistent with charger and car specs.


 


I calculate about 1W/ft power dissipation in the conduit from 0.9989 ohm/1000ft from table online. Don't know if that is enough to create a warm temp.


 


 

Expert:  Steve G. replied 1 year ago.
A colleague reminded me that that the 125% requirement is not a suggestion :) It is there for this very situation - a continuous load is going to warm up those conductors.

You really should be using a 40A breaker and #8 conductors.

Please let me know if I can help you further.

Regards
Steve
Steve G., Electrical Engineer
Category: Electrical
Satisfied Customers: 16906
Experience: 27 years in Electrical Engineering, designing electrical plans and specifications.
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