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Re: Specs for 240v outlet/breaker

Posted: Fri May 10, 2019 8:14 pm
by LeftieBiker
I'm thinking installer error, if the installation was unused before the breaker trip.

Re: Specs for 240v outlet/breaker

Posted: Mon Jun 24, 2019 5:25 pm
by RustyShackleford
Newbie here, wife is about to by a used 2018 Leaf. I'm a little confused about the Level2 charging. Nissan says that using an L2-EVSE charging cable, it will charge the 40kwh version in 8 hours, which is a net of 5000 watts. But they also say you need to install a 50amp/240v outlet. That's 12000watts. I understand that outlets (over-current protection devices, specifically) need to be oversized, and that there's some inefficiency in the charging circuit. Still 12000watts versus 5000watts seems a bit extreme. Against code even, as breakers aren't supposed to be drastically larger than the expected load (I forget what the factor is, but it's a lot less than 2.4x). Please help me to understand.

Re: Specs for 240v outlet/breaker

Posted: Mon Jun 24, 2019 5:35 pm
by davewill
RustyShackleford wrote:Newbie here, wife is about to by a used 2018 Leaf. I'm a little confused about the Level2 charging. Nissan says that using an L2-EVSE charging cable, it will charge the 40kwh version in 8 hours, which is a net of 5000 watts. But they also say you need to install a 50amp/240v outlet. That's 12000watts. I understand that outlets (over-current protection devices, specifically) need to be oversized, and that there's some inefficiency in the charging circuit. Still 12000watts versus 5000watts seems a bit extreme. Against code even, as breakers aren't supposed to be drastically larger than the expected load (I forget what the factor is, but it's a lot less than 2.4x). Please help me to understand.


OK, There are a lot on nuances in this equation. The EVSE (that's the cord you plug into the wall and the car) has a 14-50 plug on it, which nominally means a 50a circuit. The EVSE itself is able to supply 32a of current. Finally the car has a maximum draw of 27.5a. 240v * 27.5a = 6.6kW then knock a few percent off for charging inefficiencies (5-7%) and you're close enough to your 5000W estimate.

So why does Nissan seem to require a 50a circuit? Technically, the circuit must be 125% of the EVSE capacity. This means you could get by with a 40a circuit. Indeed, I have a setup exactly like that and it's pretty common. However, ask most electricians to put in a 14-50, and they'll do a 50a circuit unless there's a reason to do it differently...and I recommend that you do so unless there's a technical or economic reason to put in the smaller 40a circuit.

Re: Specs for 240v outlet/breaker

Posted: Mon Jun 24, 2019 5:48 pm
by RustyShackleford
davewill wrote:However, ask most electricians to put in a 14-50, and they'll do a 50a circuit unless there's a reason to do it differently...and I recommend that you do so unless there's a technical or economic reason to put in the smaller 40a circuit.

Oh, it's the plug (it's a 3XB3, by the way), I see. No, no real reason not to do 50amp. I'll DIY anyhow, not that it'd matter much on cost either way. I just thought 50amp sounded grossly oversized; and I'd rather work w/ 8awg than 6awg. Thanks !

Re: Specs for 240v outlet/breaker

Posted: Mon Jun 24, 2019 6:29 pm
by smkettner
50 amp is fine with lighter loads. Short circuit will trip the breaker before #12 wire melts.

Only reason to get a smaller evse would be to utilize an unused dryer outlet rated 30 amps. For this you need 24 amp evse.

Re: Specs for 240v outlet/breaker

Posted: Mon Jun 24, 2019 7:05 pm
by RustyShackleford
smkettner wrote:50 amp is fine with lighter loads. Short circuit will trip the breaker before #12 wire melts.

Wait, what, use 12awg w/ . a 50amp breaker ?


Only reason to get a smaller evse would be to utilize an unused dryer outlet rated 30 amps. For this you need 24 amp evse.

That might actually be helpful for visiting certain friends and family. So you're saying that if I look around, I can find a charging cable that'll work with this car and only need a 30amp outlet ?

Sounds like the 3XB3 will probably work with a 40amp outlet (and maybe a 30amp), but still, if has a 50amp plug and so needs a 50amp receptable, it's a code violation to install that outlet with less than 50amp breaker and compatible wire.

Re: Specs for 240v outlet/breaker

Posted: Mon Jun 24, 2019 9:01 pm
by smkettner
RustyShackleford wrote:
smkettner wrote:50 amp is fine with lighter loads. Short circuit will trip the breaker before #12 wire melts.

Wait, what, use 12awg w/ . a 50amp breaker ?
Um no.
Go ahead and wire the 14-50 with #6 or better.

Re: Specs for 240v outlet/breaker

Posted: Mon Jun 24, 2019 10:02 pm
by Jerryr
RustyShackleford wrote:
smkettner wrote:50 amp is fine with lighter loads. Short circuit will trip the breaker before #12 wire melts.

Wait, what, use 12awg w/ . a 50amp breaker ?


Only reason to get a smaller evse would be to utilize an unused dryer outlet rated 30 amps. For this you need 24 amp evse.

That might actually be helpful for visiting certain friends and family. So you're saying that if I look around, I can find a charging cable that'll work with this car and only need a 30amp outlet ?

Sounds like the 3XB3 will probably work with a 40amp outlet (and maybe a 30amp), but still, if has a 50amp plug and so needs a 50amp receptable, it's a code violation to install that outlet with less than 50amp breaker and compatible wire.


By code you will need at least 40 amps to power the 2018-2019 Nissan 120/240v. EVSE. A 40 amp circuit can only legally power 32 amps continuous and a 30 amp circuit can only legally power 24 amps continuous.

1- There is no such thing as a 40 amp only receptacle. For 40 amp 240v the receptacle used is a 14-50R the same for 50 amp 240v.

2- if you use THHN/THWN etc individual stranded wires in a raceway (conduit) you can run 8 AWG for 50 amps if the run is less than 100 ft. If you use NM-B romex you must use 6/3 with 50 amp 240v. NEC310.15(B)(16)

3- for the 120/240v OEM Nissan EVSE you can connect it to a 14-50R wired with 8AWG or 6AWG THHN in conduit or even non metallic flex conduit and use either a 40 amp or 50 amp double pole breaker.

I wired my barn outlet for my Nissan EVSE with 6AWG since I had some around and wired it to a 14-50R protected it with only a 40 amp breaker. It comes off a 60 amp sub panel and the receptacle is dedicated to the Nissan EVSE. The Nissan 120/240v EVSE draws 30 amps max.

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Re: Specs for 240v outlet/breaker

Posted: Mon Jun 24, 2019 10:32 pm
by RustyShackleford
Jerryr wrote:By code you will need at least 40 amps to power the 2018-2019 Nissan 120/240v. EVSE.

So there's no such thing as a charging cable that would only pull 24 amps (and so be ok w/ 30amp circuit) ?
There is no such thing as a 40 amp only receptacle. For 40 amp 240v the receptacle used is a 14-50R the same for 50 amp 240v.
Oh I see, so the '50' (in 14-50R) means it can handle 50amps but not that it's illegal to hook it to a small circuit (or at least to a 40amp).

Re: Specs for 240v outlet/breaker

Posted: Mon Jun 24, 2019 10:50 pm
by Titanium48
RustyShackleford wrote:So there's no such thing as a charging cable that would only pull 24 amps (and so be ok w/ 30amp circuit) ?


They do exist, but are not very common. More common are adjustable EVSEs that can be set to 32 A or to lower current settings. These are available for fixed installation and as portable units. If you are looking to minimize costs, you could consider a 16 A EVSE, which can be found for about $200.