80% Rule and Voltage

My Nissan Leaf Forum

Help Support My Nissan Leaf Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

LilSparky

Member
Joined
May 26, 2021
Messages
17
If I am using a 30a plug and breaker, but the voltage is only at 200v, does that mean I can use the full 30a? (I know that is 83%) But the main question is does the 80% apply to the voltage as well as the amperage? They both contribute to the circuit capacity, measured in watts. Also, I would plan on keeping this below 3 hours in general.
 
LilSparky said:
If I am using a 30a plug and breaker, but the voltage is only at 200v, does that mean I can use the full 30a? (I know that is 83%) But the main question is does the 80% apply to the voltage as well as the amperage? They both contribute to the circuit capacity, measured in watts. Also, I would plan on keeping this below 3 hours in general.

Do you mean 208 V, three-phase? 208V single-phase might work. I believe I've read here that the Nissan EVSE won't work with 208V @ three-phase AC power. Someone else more knowledgeable will probably chime in though, give it some time.
 
Pretty sure the answer is Not allowed -- a lower voltage does not let you pull more Amps
 
No: it is not a good idea to draw 30a (continuous) on a 30a rated circuit.
In addition, if you are only getting 200v on a 240v (rated) circuit, you have a whole other problem.
 
[/quote]

Do you mean 208 V, three-phase? 208V single-phase might work. I believe I've read here that the Nissan EVSE won't work with 208V @ three-phase AC power. Someone else more knowledgeable will probably chime in though, give it some time.
[/quote]

Yes, it's 208, but comes out at 198-200v single phase.

I have tried the Nissan EVSE and can confirm, it's a no-go at 208v.
 
LeftieBiker said:
The problem here, as I understand it, is that when the voltage is lower the car will try to pull more amps, rather than drawing fewer.

Where is that info coming from? I was under the impression the car can only pull the amperage the EVSE provides. (mine is adjustable)
 
Stanton said:
No: it is not a good idea to draw 30a (continuous) on a 30a rated circuit.
In addition, if you are only getting 200v on a 240v (rated) circuit, you have a whole other problem.
It is commercial, 208v service. And yes, I understand that continuous loads are supposed to be at 80%. My question is still if the voltage is only at 80% of the breaker rating and the total wattage load I am pulling is 80% of the breaker rating, does that work?
 
Other EVSE's such as Clipper Creek will work on 208 volts nominal, but the 80% current rule for continuous load still applies so a 30-ampere circuit and receptacle can support an EVSE with maximum current of 24 amperes. The car can draw in excess of 30 amperes at 208 volts if the EVSE allows (I have a Clipper Creek unit that allows 40 amperes so that my car can charge at its maximum rate on 208 volts at my workshop garage). The car will limit its current draw to the maximum allowed by the EVSE so you need an EVSE that allows a maximum of 24 amperes for your receptacle. To be clear, the voltage rating of the breaker has no impact on the current rating and no impact on the 80% continuous load current limitation.
 
GerryAZ said:
Other EVSE's such as Clipper Creek will work on 208 volts nominal, but the 80% current rule for continuous load still applies so a 30-ampere circuit and receptacle can support an EVSE with maximum current of 24 amperes. The car can draw in excess of 30 amperes at 208 volts if the EVSE allows (I have a Clipper Creek unit that allows 40 amperes so that my car can charge at its maximum rate on 208 volts at my workshop garage). The car will limit its current draw to the maximum allowed by the EVSE so you need an EVSE that allows a maximum of 24 amperes for your receptacle. To be clear, the voltage rating of the breaker has no impact on the current rating and no impact on the 80% continuous load current limitation.
Ok, that makes sense. I'll make sure to keep my EVSE amp setting dialed down or keep the charge to less than 3 hrs.
 
LilSparky said:
It is commercial, 208v service. And yes, I understand that continuous loads are supposed to be at 80%. My question is still if the voltage is only at 80% of the breaker rating and the total wattage load I am pulling is 80% of the breaker rating, does that work?
To expand on the previous response, it's 80% of current, not 80% of wattage. The thermal trip element is activated based on the I^2 * R heating of the thermal element, which is independent of voltage. So the tripping behavior should be very similar @ 200V vs 240V. Either way, currents above 24A for over 3 hours may nuisance trip a 30A breaker, which is not an acceptable regular behavior, hence the 24A limit.

Cheers, Wayne
 
knightmb said:
.
I believe I've read here that the Nissan EVSE won't work with 208V @ three-phase AC power. Someone else more knowledgeable will probably chime in though, give it some time.

I can confirm that the EVSE I got with my 20 Leaf wouldn’t work on 208V commercial power when I tried it.
 
LilSparky said:
GerryAZ said:
Other EVSE's such as Clipper Creek will work on 208 volts nominal, but the 80% current rule for continuous load still applies so a 30-ampere circuit and receptacle can support an EVSE with maximum current of 24 amperes. The car can draw in excess of 30 amperes at 208 volts if the EVSE allows (I have a Clipper Creek unit that allows 40 amperes so that my car can charge at its maximum rate on 208 volts at my workshop garage). The car will limit its current draw to the maximum allowed by the EVSE so you need an EVSE that allows a maximum of 24 amperes for your receptacle. To be clear, the voltage rating of the breaker has no impact on the current rating and no impact on the 80% continuous load current limitation.
Ok, that makes sense. I'll make sure to keep my EVSE amp setting dialed down or keep the charge to less than 3 hrs.
You might find that at 30a even for an hour the 30a breaker might get quite warm. I had a similar thing at work where my outlet also dropped to about 200v @ 30a, at no load it was closer to 208v but even with 24a it was close to 200v. Anyway as I normally only charged at this outlet for about an hour, I set my EVSE to 30a but of course my Leaf limited the amperage to 27.5a, as read by my EVSE. As the breaker felt quite warm as felt on the face of the breaker by the back of my finger I left the panel door open and even set a small fan pointed at the breaker, both of which kept the breaker cool to the touch and would even allow me to charge for more than 1hr, max I probably ever did was close to 3hrs. The panel was in a locked electric room. Note my EVSE plug also got quite warm, it was an L14-30 which is technically rated for 30a but does get physically hot to the touch after a couple of hours of charging. I could touch it for a brief period of time but probably wouldn't want to hold onto the metal plugs for long, of course unplugged from the wall :D
Long story short, things will get quite warm even following the 80% rule, more and it will even get warmer. If I were you I'd feel things after about a half-hour, plug, breaker, anything you can. Warm is OK but smoking hot is not, I'd also check things after an hour and even more. Once you know how your breaker, outlet and plug react you don't have to feel things every time but it is probably a good idea to check things every once in a while when pulling high currents as were talking about.
 
LilSparky said:
Ok, that makes sense. I'll make sure to keep my EVSE amp setting dialed down or keep the charge to less than 3 hrs.

Set the EVSE to 80% or less of the circuit's amperage like everyone else and be done with it. Stop looking for loopholes. The incremental speedup in charge rate is unlikely to have any meaningful impact on your ownership experience but will have a meaningful impact on your margin of safety.
 
Nubo said:
Set the EVSE to 80% or less of the circuit's amperage like everyone else and be done with it. Stop looking for loopholes. The incremental speedup in charge rate is unlikely to have any meaningful impact on your ownership experience but will have a meaningful impact on your margin of safety.

Exactly.

OP is acting as if there are no hot days where he lives.
 
Nubo said:
Set the EVSE to 80% or less of the circuit's amperage like everyone else and be done with it. Stop looking for loopholes. The incremental speedup in charge rate is unlikely to have any meaningful impact on your ownership experience but will have a meaningful impact on your margin of safety.
I wasn't looking for a loophole, just some clarification on the "rule" and some better understanding. But thanks.
 
SageBrush said:
OP is acting as if there are no hot days where he lives.

This is something I didn't take into account. At what temp will it start to be an issue? (But yes you are right, average high temperature here is 72° in July and August)
 
LilSparky said:
SageBrush said:
OP is acting as if there are no hot days where he lives.

This is something I didn't take into account. At what temp will it start to be an issue? (But yes you are right, average high temperature here is 72° in July and August)

No idea. Start from STC and add on ambient. And throw it all out the window if the electric panel is not in the shade when you are charging.

This is why Alozzy said you are shaving off your safety factor. There are too many unknowns.
 
LilSparky said:
Nubo said:
Set the EVSE to 80% or less of the circuit's amperage like everyone else and be done with it. Stop looking for loopholes. The incremental speedup in charge rate is unlikely to have any meaningful impact on your ownership experience but will have a meaningful impact on your margin of safety.
I wasn't looking for a loophole, just some clarification on the "rule" and some better understanding. But thanks.

No offense intended. But to clarify, I would not try bumping the amperage during a 2-hour charge, for example, even though the NEC definition of "continuous" is >3 hours. You'd gain very little time. 24A vs 30A isn't that big of a difference. Keep in mind a short charge implies the end-charge tapering is taking up a larger percentage of charge time anyway, which reduces any speedup even further. Every EVSE is intended to follow the 80% rule, regardless of voltage or charge duration. By exploring edge cases you'd be in largely uncharted territory and every change to the EVSE introduces a possibility of error. For such little benefit, it's not worth it, imho. Enjoy your LEAF.
 
Back
Top