Home Charger Wiring, Does This Work?

[sevengroove]

@Ladiver do you need the 14-50 for charging as well? You could explore what @timesinks did and get a couple of JuiceBoxes hooked up to that one 60A circuit breaker to load share between themselves without needing an additional switcher.

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[Ladiver]

@Ladiver do you need the 14-50 for charging as well? You could explore what @timesinks did and get a couple of JuiceBoxes hooked up to that one 60A circuit breaker to load share between themselves without needing an additional switcher.

No, I do not need two chargers. The location is a second home and I have not purchased a charger. I want to start with a 14-50 and use the Rivian mobile charger until I decide if it is worth it to install a hardwired unit. What I want to do is make sure that any electrical work done is with the big picture in mind and won't need to be re-done when I plan to add the EVSE.

 

[ajdelange]

Rely on what your electrician says. He knows what the local inspector will allow. I’m guessing (conservatively) that both the EVSE and the 14-50 are for vehicle charging and thus are both continuous loads and that the sub panel must support 120% of the sum of their loads.

Now you can put two (or 3 or 4) 60 A breakers in a 60 A subpanel (60 A in main panel), wire each to an HPWC (with No 6) and commission the group to share 48 A. That’s legit.

These loads aren’t like your 15 A utility outlets in the rest of your house or even like your clothes dryer load in that they are assumed to be on all the time. There are different rules for them.

 

[ajdelange]

I can wire the EVSE and the outlet directly to the dedicated breaker. No need for a power disconnect as that can be handled at the breaker.

It’s not needed because the EVSE is behind a 60 A breaker.

 

[timesinks]

I will certainly be interested in what he hears, but it is very common to have the sum of down stream breakers exceed the feeder breaker.

The summing of the breakers is not my objection. I understand and agree that a panel can be fed by a breaker that's smaller than the sum of its branch circuits.

My objection is that the demand-load calculation doesn't work out -- you can't just say both circuits won't be used simultaneously when you're sizing the feeder. You have to provide some level of assurance that they won't (e.g., with a drier buddy, an interlock, a two pole switch, or a listed load management system) in order to ignore the lesser of the two loads in your sizing calculation.

The idea is to protect from a guest or the next homeowner not knowing about the promise you made with your inspector and thus trying to use both circuits at the same time.

 

[jphillips97]

The summing of the breakers is not my objection. I understand and agree that a panel can be fed by a breaker that's smaller than the sum of its branch circuits.

My objection is that the demand-load calculation doesn't work out -- you can't just say both circuits won't be used simultaneously when you're sizing the feeder. You have to provide some level of assurance that they won't (e.g., with a drier buddy, an interlock, a two pole switch, or a listed load management system) in order to ignore the lesser of the two loads in your sizing calculation.

The idea is to protect from a guest or the next homeowner not knowing about the promise you made with your inspector and thus trying to use both circuits at the same time.

that is what you get by having the feeder to a sub panel and putting two breakers in there. If you turn them both on something will trip. Just like if you turned on everything in your house something would trip.

i could be wrong but I do not think I am.

 

[timesinks]

No, I do not need two chargers. The location is a second home and I have not purchased a charger. I want to start with a 14-50 and use the Rivian mobile charger until I decide if it is worth it to install a hardwired unit. What I want to do is make sure that any electrical work done is with the big picture in mind and won't need to be re-done when I plan to add the EVSE.

Honestly, if your goal is to future-proof, have the electrician:
- Run conduit from your panel to a 4-square box in the car bay
- Pull 2x 6AWG hots and an 8AWG ground through the conduit
- Terminate it on a 14-50R with a 50-amp breaker

Now you can use it immediately with the portable charger at 32A or with a specifically purchased 40A charger equipped with a 14-50P.

Then, if you want to hardwire a 48A-amp charger down the line, all you have to do is replace the receptacle face of the 4-square with a whip that goes to your hardwire charger, spliced right there in the existing box and swap the 50A breaker for a 60A one.

 

[timesinks]

that is what you get by having the feeder to a sub panel and putting two breakers in there. If you turn them both on something will trip. Just like if you turned on everything in your house something would trip.

i could be wrong but I do not think I am.

The code requires belt and suspenders. Code does not allow installing something where you rely on the breaker to be your load management system.

Edit to add: I'm not saying it won't work. I'm saying it would not meet code and is arguably unsafe. Breakers fail.

 

[jphillips97]

The code requires belt and suspenders. Code does not allow installing something where you rely on the breaker to be your load management system.

Edit to add: I'm not saying it won't work. I'm saying it would not meet code and is arguably unsafe. Breakers fail.

First let me say that I find this conversation interesting and am not being argumentative... I wanted to make the point because tone is lost in typed language and I did not want to come across wrong....

To your last sentence, breakers are designed to fail open since they are designed to protect the circuit. Do they ever fail closed? I am certain there are corner cases, but you cannot design against those remote cases.

Your breaker in each leg limits your continuous load as referenced by NEC 215.2 and allows you to calculate wire size with 25% margin (and there is additional margin built in to the conservative sire estimates anyway). I am not sure I understand your first sentence... I have seen you reference belt and suspenders more than once, but cannot find that in NEC.

I am not sure it would not meet code and I will say it is not unsafe

 

[Dirty_B]

The code requires belt and suspenders. Code does not allow installing something where you rely on the breaker to be your load management system.

Edit to add: I'm not saying it won't work. I'm saying it would not meet code and is arguably unsafe. Breakers fail.

Trying to learn something: so when I have one circuit say in my great room, 15amp breaker, with say 4 diff wall outlets. Isn't the breaker my load management system? If I decide to plug a hair dryer, a microwave, a heating blanket into 3 of the 4 outlets... And pull 20amps?

 

[timesinks]

First let me say that I find this conversation interesting and am not being argumentative... I wanted to make the point because tone is lost in typed language and I did not want to come across wrong....

To your last sentence, breakers are designed to fail open since they are designed to protect the circuit. Do they ever fail closed? I am certain there are corner cases, but you cannot design against those remote cases.

Your breaker in each leg limits your continuous load as referenced by NEC 215.2 and allows you to calculate wire size with 25% margin (and there is additional margin built in to the conservative sire estimates anyway). I am not sure I understand your first sentence... I have seen you reference belt and suspenders more than once, but cannot find that in NEC.

I am not sure it would not meet code and I will say it is not unsafe

Yes, breakers can fail closed and the code deals with this by not allowing you do put more than the intended load on a wire. In this way, you'd have to have two failures instead of just one to be in a really bad state (a short circuit and a failed breaker at the same time).

By definition in the code, the receptacle intended for an EVSE and the circuit for a hardwire EVSE would both be continuous loads. It's not an either-or thing unless there is some additional equipment to ensure it's operated either-or. The code doesn't care what you intend to do in terms of not using both at the same time. That's in large part because what you intend to do may not be what your house guest or future owner will do.

625.41 Overcurrent Protection. Overcurrent protection for feeders and branch circuits supplying EVSE [...] shall be sized for continuous duty and shall have a rating of not less than 125 percent of the maximum load of the equipment.

Your proposed subpanel with two EVSE circuits (one for a hardwire outlet and one for a receptacle) without an interlock or load management system, requires that you size the feeders to 125% of the maximum load of the equipment. That's all the equipment. That's the code.

Trying to learn something: so when I have one circuit say in my great room, 15amp breaker, with say 4 diff wall outlets. Isn't the breaker my load management system? If I decide to plug a hair dryer, a microwave, a heating blanket into 3 of the 4 outlets... And pull 20amps?

Most people have at least marginal awareness that it's not a great idea to run multiple "power hungry" things on one circuit. That awareness is the first line of defense. This is also only something we do for relatively low amperage circuits (15A and 20A). Most things at higher amperages require dedicated circuits.

People also mistakenly think if you run 16A on a 15A breaker that it'll pop right away. In reality, for a breaker to trip right away, you typically need around 5-6x the handle rating -- that would be 75-90A on a 15A breaker. The further over 15A, the faster it should trip. If you're only an amp or two over, it may well not trip at all.

 

[jphillips97]

Yes, breakers can fail closed and the code deals with this by not allowing you do put more than the intended load on a wire. In this way, you'd have to have two failures instead of just one to be in a really bad state (a short circuit and a failed breaker at the same time).

By definition in the code, the receptacle intended for an EVSE and the circuit for a hardwire EVSE would both be continuous loads. It's not an either-or thing unless there is some additional equipment to ensure it's operated either-or. The code doesn't care what you intend to do in terms of not using both at the same time. That's in large part because what you intend to do may not be what your house guest or future owner will do.



Your proposed subpanel with two EVSE circuits (one for a hardwire outlet and one for a receptacle) without an interlock or load management system, requires that you size the feeders to 125% of the maximum load of the equipment. That's all the equipment. That's the code.



Most people have at least marginal awareness that it's not a great idea to run multiple "power hungry" things on one circuit. That awareness is the first line of defense. This is also only something we do for relatively low amperage circuits (15A and 20A). Most things at higher amperages require dedicated circuits.

People also mistakenly think if you run 16A on a 15A breaker that it'll pop right away. In reality, for a breaker to trip right away, you typically need around 5-6x the handle rating -- that would be 75-90A on a 15A breaker. The further over 15A, the faster it should trip. If you're only an amp or two over, it may well not trip at all.

I cannot find an example of a breaker failing closed.... Given the bimetal plate construction and the physics of heating, it is hard to imagine one failing closed. Maybe there is a distinction for hard wired appliances but you have redundancy by the fact that you have a sub panel down stream from your first breaker... It is very common for down stream subpanels to add to higher current draw than the feeder breaker...

The hardwired charger would be a continuous load on the circuit it is isolated to on the second 60A breaker. The receptacle would be isolated to its 40A breaker. In each of these cases the wire would have to be sized accordingly.

You can download trip curves for any breaker... You are correct that they will allow excess current for a finite amount of time, but this margin is built into how we size wires to breakers. Breakers open fast for extremely large currents based on induced magnetic fields and open slower based on thermal mechanisms for lower currents but still above rated load. This allows for the immediate arrest of excessive current, but slower for lower currents to allow for transients when you switch things on or off. Another reason for the NEC puts a lot of margin built into wire size.

I am not an electrician so I do not know code, but I do have a PhD in engineering and taught at the college level so I know the engineering side, but I do not know the NEC...

 

[Ladiver]

OK, I spoke with a City Inspector and he said if both circuits are going to be used for EV charging (even if not at same time), the sub-panel (50A and 60A) should be supplied with a 125A breaker.

 

[jphillips97]

OK, I spoke with a City Inspector and he said if both circuits are going to be used for EV charging (even if not at same time), the sub-panel (50A and 60A) should be supplied with a 125A breaker.

I stand corrected but I would of asked him the follow up question of how fits that affect my up stream main breaker? At some point, you have the issue the sum being greater than the feeder breaker. No way to avoid it.

 

[Ladiver]

I stand corrected but I would of asked him the follow up question of how fits that affect my up stream main breaker? At some point, you have the issue the sum being greater than the feeder breaker. No way to avoid it.

I completely agree with you. If the house only has 200A service, then I am “dedicating” 62.5% of the usable power to a circuit for EV charging. I bet there is more than 80A worth of breakers in the current panel. I know there are 2 garbage disposals (which should be on dedicated 20A) and a steam oven with a dedicated 30A. There’s 70A, guess I need to go buy some candles because I can’t put in a 15A for lights.

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