Mismatched plug and circuit amperage ratings, but it's ok?

[macchiaz-o]

There are a number of EVSEs on the market that include a NEMA 14-50 or NEMA 6-50 plug. Some of them support current limiting all the way down to 16A, just in case your circuit is only rated for 20A (for instance). Here's one of them: ChargePoint Home Flex

On some units, current limiting is configured via hardware, like dip switches, while in other cases, limits are set via software. ChargePoint says their unit is configured via app on your phone. Isn't it unsafe to have a plug designed for a higher rating than the circuit it connects to? I mean, the plug is designed for a 50A circuit, but we're allowed to use it on a 40A circuit instead? Or even lower in some cases, as implied by this text from the ChargePoint Home Flex marketing page:

Have your electrician install it indoors or out using a NEMA 6-50 or 14-50 plug, then set the appropriate charging speed in the app — up to 50 amps.

Note that on another page on their site, it says that for use under 40A, your electrician will need to hardwire... Anyway, to me, it seems irresponsible to market it this way. They're not alone, either. I've seen similar marketing on some other EVSEs, as well as products targetted mostly for RV owners while sometimes purchased by EV owners. For example, this 30M to 50F adapter:

Is this sort of thing addressed by the National Electric Code? I've been in hotel rooms where standard 15A outlets have a sticker on them saying "Max 2A" or something along those lines. Maybe that labeling is sufficient... Just trying to sort this out for myself.

I plan to connect Ford's mobile charger to either a 240V 20A or 30A circuit in my garage, but I'm doubtful Ford is including the NEMA plug for either of those. I'd prefer not to hardwire. At the same time, I don't want to "cheat" through 14-50 receptacles on a 30A circuit, if -- as I suspect but am unsure -- that is considered cheating.

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[JamieGeek]

I have two EVSE's that I have adjustable current limits. (Both plug in the same plug and I can only use one at a time.)

Both of them are set to currents less than the breakers (30 amp breakers and both EVSE's are set to about 28 amps).

The Bosch EVSE can go as high as 32 amps, and the Juicebox can go to 60 amps (the Clipper Creek I keep in the car for campground charging as its portable and fixed at 24amps).

 

[macchiaz-o]

Those are good examples -- how is your setup "safe" electrically? I guess what I mean by that is, you understand that you shouldn't set the Juicebox to 60A since you know you've wired it to a plug that is rated for less, and adapted plug to a receptacle that is rated for way less... But what if someone else were to try and use it, being less knowledgeable about the mismatched plugs and circuits?

Also, you mentioned setting a limit of 28A on a 30A circuit. I thought on that circuit that your maximum continuous current draw should be limited to 24A, to avoid overheating the wiring.

 

[JamieGeek]

Its safe because the breakers protect the wiring--that is their job. Thus if I set either too high the breakers will trip long before anything happens to the wiring. Same thing will happen on any normal 15 amp circuit: Plug the toaster oven and a hair dryer into the same 15 amp circuit and put them both on high (each draws about 12 amps)... (We trip our bathroom breaker once in a while when more than one person use a hair dryer at the same time.)

Its been a while--I had that all setup back in 2013 when I leased the Focus Electric so I may have them set a little less than 28 amps.

Of course you may ask: why do I have so many? LOL (The Bosch was the first one which I got through our power company: To have a 2nd meter installed, wired and including the Bosch EVSE the total bill was something like $2600 of which I only paid $100 due to rebates and incentives. The JuiceBox was free--the Focus Electric forums had a contest start a blog and win a JuiceBox: I won. I paid full price for the Clipper Creek because I wanted a 240V capable portable EVSE in the car--at the time both the ones that come with the Focus Electric and C-Max Energi only worked with 120V.)

 

[jlauro]

He said the charge rate is 28 amps. He didn't say what the wire is rated for. If it is 10 gauge copper wire to the outlet then it is safe.

Anyways, it's not only for safety why you might want to run a charger at a rate lower than it's maximum. For example, if you have solar and if you pull too much current it will take from the grid which unless you have 1:1 net metering with no transport charges you don't want to do... or you are concerned that the faster you charge the more it will deteriorate your batteries.

If someone else tried to use it, it would either or work because they never went over 30 amps, or it would trip the breaker and be safe.

Breakers are typically rated for 125% of continuous load. So, for 24 amps continuous load a breaker is rated for 30 amps. However, you can also do 100% continuous load if it never goes over that. An EV charger never goes over it's configured draw, so you don't need the circuit at 25% higher like you would for a dryer or other similar appliance. I assume the other 2 amps are also there for the charger electronics and overhead outside of what is given to the car.

 

[macchiaz-o]

Thanks for the feedback, guys. This helps me feel more comfortable with this major new appliance in my garage.

 

[silverelan]

The Mach-E will take up to 48A at 240V. The car's onboard charger will communicate with the external power supply and negotiate the electrical draw. So regardless if the wall charger is 32A or 60A, it'll take the full 32A if that's what available or it'll limit the draw to 48A out of the available 60A.

It gets more complicated using a Tesla adapter. You'd need a 48A rated JDapter or else you run the potential of frying a 40A rated adapter.

 

[macchiaz-o]

Speaking of Tesla, on their web site they sell adapters with many of the common NEMA plugs for $35 each. They describe them as simply plug and play. I'm guessing each Tesla wall adapter has a way of communicating its current limit to the EVSE. This could be easily accomplished with one extra pin and a resistor (for example).

Best case scenario for me would be if Ford sells the same accessories for its mobile charger. All they've said so far is that two adapters are included, which I'm assuming are just for 120V 15A and 240V 40A circuits. I've already got one circuit in the garage whose wiring is suitable for 240V 30A, so I'd love to use that and minimize any rewiring.

 

[JamieGeek]

Except that the adapters would only know what they are rated for and not the circuit they are plugged into.

 

[macchiaz-o]

Right. Isn't that ideal? Assuming an electrician wired up the home correctly, the outlet would have a receptacle rated to the wiring. Then the EVSE with the correct plug would match the electrician's work and maintain safety while also preventing breakers from tripping.

 

[JamieGeek]

Yes that is ideal but how many homes have square corners?

Does the Tesla EVSE also have a way to manually set its reported current since someone may have other reasons (as stated above) for choosing a different current than the max the circuit can draw?

 

[macchiaz-o]

Tesla's EVSE has an internal dial to limit current, and like other plug-in EVs, rate can also be limited through the car's user interface.

 

[JamieGeek]

Ah ok--LOL yeah I have a bunch of experience in non-Tesla EV's (Mostly Ford plugins really..and the Bolt)

 

[zhackwyatt]

There are a number of EVSEs on the market that include a NEMA 14-50 or NEMA 6-50 plug. Some of them support current limiting all the way down to 16A, just in case your circuit is only rated for 20A (for instance). Here's one of them: ChargePoint Home Flex

On some units, current limiting is configured via hardware, like dip switches, while in other cases, limits are set via software. ChargePoint says their unit is configured via app on your phone. Isn't it unsafe to have a plug designed for a higher rating than the circuit it connects to? I mean, the plug is designed for a 50A circuit, but we're allowed to use it on a 40A circuit instead? Or even lower in some cases, as implied by this text from the ChargePoint Home Flex marketing page:



Note that on another page on their site, it says that for use under 40A, your electrician will need to hardwire... Anyway, to me, it seems irresponsible to market it this way. They're not alone, either. I've seen similar marketing on some other EVSEs, as well as products targetted mostly for RV owners while sometimes purchased by EV owners. For example, this 30M to 50F adapter:

Is this sort of thing addressed by the National Electric Code? I've been in hotel rooms where standard 15A outlets have a sticker on them saying "Max 2A" or something along those lines. Maybe that labeling is sufficient... Just trying to sort this out for myself.

I plan to connect Ford's mobile charger to either a 240V 20A or 30A circuit in my garage, but I'm doubtful Ford is including the NEMA plug for either of those. I'd prefer not to hardwire. At the same time, I don't want to "cheat" through 14-50 receptacles on a 30A circuit, if -- as I suspect but am unsure -- that is considered cheating.

I've been thinking the same thing. There is nothing stopping someone from putting an NEMA 5-20 plug on a 15 amp circuit. I would assume that is against code.

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