Also for a load that runs more than 4 hours, you are required to operate the
breaker at 80% or less of its rating. There is no gain from putting in a
smaller breaker because the car will draw only the power that the EVSE is set
to allow. Setting this lower keeps everything cooler so it lasts longer.
Oversize wire also keeps things cooler and the largest breaker allowed improves
future uses.
Phil
On Thursday, February 12, 2026 at 02:24:44 PM EST, Jay Summet via EV
<[email protected]> wrote:
On 2/12/26 13:40, EV List Lackey via EV wrote:
> On 12 Feb 2026 at 9:22, Thos True via EV wrote:
>
>> If you are connecting a 30A charger, it would be wise to choose a 30A
>> circuit breaker, rather than a 50A.
>
> I'm not a pro electrician, so please forgive me if I'm speaking out of turn,
> but wouldn't you use a 40a breaker there?
>
Yes, that is correct. You need a 50 amp breaker for a 40 amp EVSE and 40
amp for a 30A EVSE to prevent nuisance trips.
He also didn't mention what wire size to use. But if you install a NEMA
14-50, you should use the correct (50 amp rated) wire gauge (size can
change depending upon the length of the run, but typically be a 6AWG or
4AWG for longer runs to reduce resistance losses).
I suspect it may be against code (but safe) to downsize the breaker
(smaller than the wire/outlet requires).
So if you have a 30 amp EVSE, using a 40A Breaker isn't a bad idea to
trip faster if the load goes well above expected, BUT, if somebody plugs
anything else into the NEMA 14-50 that expects to be able to get 50 amp
power, it will trip the 40A breaker quickly.
What you CAN'T do is use the incorrect (too small, lower amp rating)
wire size...that's unsafe, especially if somebody later swaps out the
40A breaker to a 50A breaker because they see the 14-50 at the other end
and don't pay attention to the wire size.
Jay
_______________________________________________
Address messages to [email protected]
No other addresses in TO and CC fields
HELP: http://www.evdl.org/help/
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20260213/b1d003bd/attachment.htm>
_______________________________________________
Address messages to [email protected]
No other addresses in TO and CC fields
HELP: http://www.evdl.org/help/
