Charging multiple EV’s at home

[timesinks]

I order to comply with code:

• If the amperage can be adjusted it cannot have a cord and plug.
• If a unit has the capability to be configured for different amperages, it must be hardwired to meet code. Even a hardwired unit cannot let the user do the adjustment.

That is absolutely how I'd read the code, but that doesn't seem to be how things work in practice. Look at the ChargePoint Flex or the Juice Box 48. Both have installer-configurable amperages. Both come with cords.

The manufacturers are not having problems getting their products safety listed with the cord and the install manuals that instruct the user that it's ok to use the cord if you configure the amperage correctly.

So what gives? Well, partly, it's a plug-and-cord appliance. And the inspector (in many? most? definitely my area) makes sure the proper receptacle was installed with the proper gauge and rating of wire properly protected and connected to a properly sized circuit breaker. And that's it. They give very little consideration to what you plug into that outlet once they're gone.

The code is only enforceable to the extent that it has been adopted by your local jurisdiction -- it may well be that the language the AHJ used in whatever law or resolution they adopted applies the NEC to the permanent structure but not the appliances in it. So just because the NEC has rules about a plug-and-cord appliance doesn't necessarily mean they're applicable in your local jurisdiction. As @ajdelange has said repeatedly, your local electricians should know how your local inspectors are interpreting the rules. If you want to DIY, call your inspector before doing the work and ask. You should do that anyways if you're unsure in order to save yourself from an unnecessary round of corrections.

In the end, it's listed equipment (I hope) being installed according to the manufacturer's instructions. In the real world, you are just not likely to run into problems with this. I have not heard of anyone actually failing an electrical inspection for having user configurable amperage for their plug-and-cord EVSE (or for having a plug-and-cord EVSE that's screwed onto the wall).

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[Rivians]

You asked how people were dealing with charging multiple vehicles at home. I responded with what I did when I built, but the same thing could be done in existing construction. If your existing panel doesn't have enough amperage to handle the necessary circuits, the panel can be upgraded. That can be expensive, but it's the only way to charge two vehicles simultaneously at full Level 2 speed.

I think you need some extra capacity in the circuit to avoid tripping the fuse. That is why Tesla recommends a 50-amp line for charging at 40 amps and a 100-watt line if you have the dual charger which draws 80 amps.

If you plug two cars in at once to a line that doesn't have capacity for both cars, they may each try to draw as much current as the line provides, thereby tripping the fuse. If you plug two 40-amp cars into one 50-amp line, I doubt if the cars will know to draw only 25 amps each. I could be wrong, but I'd check with the manufacturer before trying it.

In the Tesla you can set the max Amp so that this never occurs. I'd hope the same would be for the Rivian as well as in the rare occasions I'm charging both my Tesla and Rivian at the same time I'd want to be able to cap the Amp for both so it never trips.

 

[ajdelange]

I think you need some extra capacity in the circuit to avoid tripping the fuse. That is why Tesla recommends a 50-amp line for charging at 40 amps and a 100-watt line if you have the dual charger which draws 80 amps.

The extra 20% is a requirement of the code for any circuit that is on more that 3 hours at a time. The code defines vehicle charging equipment as being on more than 3 hours continuously whether it is or isn't. This is why EVSE connected to a 50A circuit must limit what the vehicle can draw to 40A etc.

If you plug two cars in at once to a line that doesn't have capacity for both cars, they may each try to draw as much current as the line provides, thereby tripping the fuse. If you plug two 40-amp cars into one 50-amp line, I doubt if the cars will know to draw only 25 amps each. I could be wrong, but I'd check with the manufacturer before trying it.

That's why EVSE is required to manage this. The Tesla Gen 2 HPWC can go on a circuit as big as 100A in which case it can charge at up to 80A (and some older Teslas did). You could put more than one HPWC on that same circuit and if you did and plugged in a car drawing the max 48A that the newer cars are limited to then it gets 48A. Now if you come along with a second car set for 48 A charging and plug the paired HPWC into it the HPWC will indicate to the car that it may not charge faster that 80 - 48 = 32A and the second car will charge at 32 for a total of 80A. When the first car finishes the HPWC will tell the second car and it will get the full 48A.

The later HPWC (Gen 3) require a separate branch for each HPWC with a maxium breaker size of 60 A implying 48A maxium to a car plugged in. But sharing can still be worked. A second HPWC would also have a 60 A breaker and thus a limit of 48A but you can (or will be able to when the new firmware is downloaded) be able to limit the total draw from these two HPWC to whatever you like. If you set that limit to 80 A you could, then, put the two branch breakers into a sub panel protected by a 100A breaker confident that whoever plugged in when no more than 80 A would ever flow through that breaker. Other manufacturers have other sharing schemes. I don't know what, if any, sharing the Rivian charger may allow or how they implement it.

In the Tesla you can set the max Amp so that this never occurs. I'd hope the same would be for the Rivian as well as in the rare occasions I'm charging both my Tesla and Rivian at the same time I'd want to be able to cap the Amp for both so it never trips.

The code and your insureance company (from whom the code ultimately originates) do not grant you the intelligence to be able to do this safely. They are right in this. I consider myself a reasonably intelligent guy (but I'm not getting any smarter as I get older) and am, at the same time, pretty sure I'd manage to stuff this up eventually. Nevertheless I too hope that Rivian will grant us control of charging rate in reasonably small steps (1 kW) as there are times one does not want to charge at the full rate available for a variety of reasons.

 

[Trekkie]

The extra 20% is a requirement of the code for any circuit that is on more that 3 hours at a time. The code defines vehicle charging equipment as being on more than 3 hours continuously whether it is or isn't. This is why EVSE connected to a 50A circuit must limit what the vehicle can draw to 40A etc.

This is to get UL listing otherwise you can't install anything. It's not just limited to EVSE either, this is across the board in the US if you plug something in the circuits are sized 20% over the max draw of the device.

Which is why extension cords and outlet adapters get us into trouble a lot.

 

[ajdelange]

This is to get UL listing otherwise you can't install anything. It's not just limited to EVSE either, this is across the board in the US if you plug something in the circuits are sized 20% over the max draw of the device.

No, this is part of the NEC. It applies only to loads that are not "intermittent". Intermittent is defined as on for less than three hours. There is, thus, no requirement that a clothes dryer that draws 28 A be on a 40 amp circuit. And NEC is limited to premises wiring. Not the equipment that you may plug into it.

UL (or other laboratory listing) is a separate matter. The laboratory that does the test cannot test your premises wiring and thus what sort of branch the equipment may be plugged into or hard wired to cannot enter into their testing procedures.

Now I believe that one of the reasons the Article 625 is so screwed up is that EVSE is sort of simultaneously fish and fowel. There are sub articles on what sort of tool is required to remove EVSE to determine if it is portable or "fastened in place" etc.

If I ask an electrician to install a 14-60R in my garage and he does so with a 60A breaker and with the proper size wire he is completely within code and the installation will pass inspection. If I go buy a laboratory rated plug equipped 48 A charger (which I can do) what happens if I plug it in to that outlet. Have I violated NEC? Damned if I know.

 

[Wayne]

A good friend of mine charges two EVs at his home. But he also built a hydro generator plant to power two houses, an extensive shop, and his charging station. It helps to have a 200' waterfall in your backyard.

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