l6sman
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Re: Installing 4-prong charger on 3-wire 240V distribution

Sun Dec 27, 2020 10:16 am

wwhitney wrote:
Sun Dec 27, 2020 9:45 am
l6sman wrote:
Sun Dec 27, 2020 9:03 am
OK thanks. Then does it hurt using the original Nissan charger since it seemed to work fine?
To my knowledge, the only hazard the NEC is seeking to avoid with the requirement of a maximum 80% continuous load on a breaker is the hazard of repeated nuisance tripping. This is a real hazard, as if the user gets in the habit of just resetting the breaker, then the breaker will wear, and the user will not be able to tell if it starts tripping for some other reason.

Also, I believe you mentioned that your garage is fed by a 30A 120V/240V circuit, and that it has other loads. Even if your breaker holds with the continuous 27.5A load of the Nissan Leaf alone, there is a significant probability of it tripping when other loads happen to come on. I.e. just because you tried the garage door opener once doesn't mean that there isn't a 1% or 5% chance of it tripping each time you use the garage door opener. Sticking with the 24A continuous EVSE would give you more headroom.

Lastly, I don't know what pilot signal the Nissan EVSE uses. If it advertises 30A or 32A, and you ever plug in another EV that can charge at that rate, you're quite likely to trip the 30A breaker.

So for those reasons, it is more prudent to use the 24A continuous EVSE, rather than the Nissan EVSE.

Cheers, Wayne

PS For those less familiar with the NEC, the requirement for continuous loads is written in terms of providing conductors with an ampacity (amp capacity) of 125% of the continuous load. Which at first glance suggests that the conductors themselves are in need of upsizing for continuous load. But basically every instance of this requirement has an exception stating that if the circuit is supplied by a "100% rated" breaker, then the conductors may be sized at 100% of the continuous load. A "100% rated" breaker consists of a single breaker in its own enclosure (to avoid heat buildup from other breakers) that has been tested to hold at a continuous current matching its rating. [And they basically don't exist smaller than 100A.] This shows that the continuous load requirements are due to the limitations of standard breakers, and nothing else.

Thanks all. I really appreciate your experience and insight :)

Flyct
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Re: Installing 4-prong charger on 3-wire 240V distribution

Sun Dec 27, 2020 11:23 am

Another factor to consider is that breakers can fail to trip even at their rated capacity. Contacts have been known to become welded shut. Federal Pacific are the worst for failing to trip when overloaded and causing fires.

Bottom line, NO MORE THAN 24 AMPS CONTINUOUS ON A 30A Circuit. Don’t risk it.

This is what I found on a breaker in my shed sub panel at my vacation cabin when I smelled electrical burning. Breaker never tripped and device continued to work. I had to replace the sub panel due to burnt back plate where breakers connect.

Image


This is a picture of newly installed 60A sub panel before breakers were labeled. Top left 60A breaker is (Now Labeled) MAIN and bottom right 40A protects the 14-50R receptacle for the Nissan OEM ESEV.

Image
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GerryAZ
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Re: Installing 4-prong charger on 3-wire 240V distribution

Sun Dec 27, 2020 1:44 pm

Flyct makes a very good point with photos. I had a similar situation at the first house I owned in Phoenix in the mid 1980's. I think the panelboard was a Sylvania (which I believe was made by Federal Pacific). In my case, the breaker eventually tripped and I was able to carefully clean up the bus bars and panel interior and then replace the breaker. That overheating could happen at any connection in the circuit so don't exceed 80% continuous load. The Nissan dual-voltage EVSE gives a pilot signal for 30 amperes at 240 volts and 12 amperes at 120 volts so you need a 40-ampere circuit for 240V charging and at least 15-ampere circuit (with nothing else being used on the circuit) for 120V charging.

Perhaps I was not clear in previous posts, but the 2019 (I assume 2018 and 2020 would be similar) can exceed 27.5 amperes at nominal 240 volts and exceed 30 amperes at nominal 208 volts if EVSE pilot signal allows. The Nissan unit will not function on 208 volts, but the car could easily exceed 28 amperes if the voltage drops below 240 and approach 30 amperes if the voltage is down near 230 volts. Therefore, you need an EVSE with a pilot signal which corresponds to 24 amperes as a maximum to charge from a 30-ampere circuit.
Gerry
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wwhitney
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Re: Installing 4-prong charger on 3-wire 240V distribution

Sun Dec 27, 2020 2:03 pm

GerryAZ wrote:
Sun Dec 27, 2020 1:44 pm
That overheating could happen at any connection in the circuit so don't exceed 80% continuous load.
As your experience and Flyct's experience show, overheating at a poor electrical connection can and does happen. But I don't see how that has much relation to the 80% continuous load question. The heat dissipation at the connection is I^2 * R, so increasing the current by 25% will increase the rate of heating by about 56%.

But it would be a pretty narrow range of values of R for which 24 amps wouldn't be a problem, while 30 amps would be a problem. And if the poor connection is at the breaker itself, I would expect it to trip sooner with the higher current, since its thermal trip curve would have less headroom remaining. Flyct's example shows that you can get destructive heating effects at currents quite a bit lower than will trip the breaker (edit: so staying at 80% is not a safeguard against this particular problem).

Cheers, Wayne

GerryAZ
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Re: Installing 4-prong charger on 3-wire 240V distribution

Sun Dec 27, 2020 2:26 pm

wwhitney wrote:
Sun Dec 27, 2020 2:03 pm
GerryAZ wrote:
Sun Dec 27, 2020 1:44 pm
That overheating could happen at any connection in the circuit so don't exceed 80% continuous load.
As your experience and Flyct's experience show, overheating at a poor electrical connection can and does happen. But I don't see how that has much relation to the 80% continuous load question. The heat dissipation at the connection is I^2 * R, so increasing the current by 25% will increase the rate of heating by about 56%.

But it would be a pretty narrow range of values of R for which 24 amps wouldn't be a problem, while 30 amps would be a problem. And if the poor connection is at the breaker itself, I would expect it to trip sooner with the higher current, since its thermal trip curve has less headroom remaining. Flyct's example shows that you can get destructive heating effects at currents quite a bit lower than will trip the breaker.

Cheers, Wayne
Thanks for your reply. I only mentioned the 80% value because it is generally considered OK to load a circuit up to that level. Obviously, a loose connection may overheat at loads much lower than 80% of the circuit rating so it is prudent to check for overheating when charging (especially the first time using an unknown circuit).

In my case with the Sylvania panel, I was probably lucky the circuit was fairly heavily loaded and the panelboard was outside in high ambient temperature so the breaker tripped before more damage was done.

Cheers,
Gerry
Gerry
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DaveinOlyWA
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Re: Installing 4-prong charger on 3-wire 240V distribution

Wed Dec 30, 2020 7:37 am

l6sman wrote:
Sun Dec 27, 2020 9:03 am
wwhitney wrote:
Sun Dec 27, 2020 8:20 am
l6sman wrote:
Sun Dec 27, 2020 7:42 am
Based on the conversations above and the fact that the Nissan charger didn't fail on a 30amp breaker, does anyone know whether the Nissan charger has built-in intelligence that allows it to charge at a lesser rate? I'm thinking it may since the breaker didn't trip.
No.

A properly functioning 30 amp breaker may trip at 27 amps continuous after an hour. Or it may never trip at 35 amps continuous. The variation depends on manufacturing tolerances and the ambient temperature of the breaker (which in turn depends on how other breakers in the enclosure are loaded).

This variation in breaker trip characteristics is the reason for the 80% continuous load limit in the NEC.

Cheers, Wayne
OK thanks. Then does it hurt using the original Nissan charger since it seemed to work fine? There is no way to tell the Leaf to only charge at 24 amps instead of 30 amps is there?
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redtailhawk
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Re: Installing 4-prong charger on 3-wire 240V distribution

Wed May 26, 2021 12:51 pm

Thanks so much for all the info here. New leaf owner - 2021 SV plus and I Was scratching my head wondering why my 220 adapter would not work. Rewired and works like a charm.

hbquikcomjamesl
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Re: Installing 4-prong charger on 3-wire 240V distribution

Wed May 26, 2021 3:28 pm

l6sman wrote:
Sun Dec 27, 2020 9:03 am
There is no way to tell the Leaf to only charge at 24 amps instead of 30 amps is there?
Of course there is. So long as you have a sufficiently sophisticated charging station. The maximum charge rate is set in the handshake between the EVSE and the OBC, but to know that, the EVSE needs to know what to tell the OBC.

On some units, that's done with a front panel switch. Or a smartphone app. On a Grizzl-E (which is what I have), it's done with an internal DIP switch, which the nice people at United Chargers Canada will be happy to do for you, before they ship it.

And the general rule of thumb is to avoid continuous loads of more than 80% of a circuit's rated capacity. And never, ever, replace a breaker with a higher rated one unless the wires are actually heavy enough to handle the higher current.

As to the original question, on all current 4-wire single-phase 240V sockets, at least in the U.S. (and probably Canada), two lines are hot, the third is neutral, and the fourth is safety ground, while on all current 3-wire single-phase 240V sockets, it's two hots and a safety ground. There are obsolete 240V single-phase sockets that were used for electric clothes dryers back in the 1960s, with two hots and a neutral (if you wanted a safety ground, you presumably bonded the frame of the dryer to a cold water pipe). A Grizzl-E doesn't need a neutral, as everything runs on 240VAC, but it can be bought with either a 3-wire or 4-wire plug; if you buy it with a 4-wire plug, the neutral doesn't actually connect to anything inside the case.
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