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I have an electric vehicle mobile charger that is plugged in to a dedicated 30 Amp circuit.

When I’m done charging, I undock the charger from the car. I leave my mobile charger plugged into the 14-50 receptacle.

Instead of unplugging and plugging in the mobile charger from the receptacle, I flip the breaker off/on depending on when I’m charging.

Is this bad practice? I did some research and I read that a breaker has a mechanical duty of 4000 - 6000. And can be tripped 3 or 4 times before it has to be replaced. I also read that everytime you switch it on/off it damaged the breaker a little bit.

Are any of those findings accurate? Should I just leave the breaker on?

Update

Based on comments and responses below... I have changed the receptacle to a 14-30 (note: the existing wires are 10 AWG.) Also, the car and the app limits the charging current to 24A max, 80% of 30. (Before, when I had the 14-50 set up, I had to manually reduce the charging current to 24A b/c the max was 40A, 80% of 50.

14-30 receptacle

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    If it's a choice between unplugging it or turning off the breaker, flip the breaker even if it's not rated for that as unplugging it often will quickly wear out the outlet. Ideally though you can just leave it plugged in and on.
    – KMJ
    Commented Dec 20, 2022 at 8:02
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    Wait. You have a 14-50 receptacle on a 30A breaker? That's illegal! How do you know the charge system is limiting to 24A (5.8kW)? And if you're using that socket because you're using the travel charger that came with the car and are too cheap to buy a correct 30A dongle plug, you're overloading the circuit as well. The dongle plug tells the car the available amps based on plug shape. . Commented Dec 20, 2022 at 19:07
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    @milesmeow you might, but it's still not legal. The next thing to plug in there might draw full current. Do please clearly label the port as 24A max, which doesn't make it legal but might help avoid future problems.
    – Criggie
    Commented Dec 20, 2022 at 22:46
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    @milesmeow, and what do you suppose will happen when the charger resets itself and tries to draw 50 amps through those 30-amp wires?
    – Mark
    Commented Dec 21, 2022 at 2:50
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    Hmm... my understanding is that the NEC allows to put a 50A receptacle on a 30A circuit as long as the wire is correct. It is when you put a 30A receptacle on a 50A circuit that you get into trouble. The receptacle, and wire for that matter, can be over rated, just not underrated. Commented Dec 21, 2022 at 17:03

3 Answers 3

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TLDR: That's fine as long as there's no current

...flowing through the circuit when you flip it. Interrupting EV current would be bad for the breaker. Some breakers are listed to interrupt current, but a 2-pole 30A won't be one of them.

Be VERY careful with EV ampacity

It is not important to have a Super Fast EV charger. This is an EV myth. Even a 240V/15A circuit is good enough, when backed up with DC fast charging for rare exceptions that 90 miles per 12 hours is not good enough.

What is important is not burning your house down.

To start with, charging must be sized for the available amps in the service. That is decided by a NEC Article 220 Load Calculation, not "some other method lol".

Next, Codes need to be followed. The socket size needs to match the breaker size. A 30A breaker with 30A wiring needs a NEMA 6-30 or 14-30 socket, not a 50A socket. Many people use the "travel unit" that was supplied with their car. Those have exchangeable dongle plugs so you can plug into any available plug. They make a wide variety of dongle plugs. It's extra important for socket to match breaker because the dongle plug tells the car the safe amps it can draw based on the socket size! By improperly using a 14-50 socket with a 30A wire/breaker, you told the car "you are on a 40A or 50A circuit".

The travel unit, being a travel unit, comes with included dongle plugs for the 2 sockets most often seen when traveling: the common one, and the large RV plug NEMA 14-50 found at every RV campsite. Because it's for travel. This has confused many people. Actually, the "standard" EV socket will vary to match what your house is able to provide (NEMA 6-15, 6-20, 6-30 or 6-50/14-50) and EVs don't use neutral so a 4-wire socket is wasted. You can buy a wide variety of dongle plugs; they're not expensive and they will tell the car the correct charge rate.

So I say, emphatically - clean up your act and get legal. This is nothing to fool around with. You seem fastidious and want things in a certain order/way, wanting to turn a breaker off to save 2 watts - I think you have a whole lot more important stuff you need to fix first.

After doing a Load Calculation, either change the receptacle and breaker to one appropriate for your available power, or if 40A is available, rewire the circuit with 40A wire and breaker. (the travel EVSE assumes a NEMA 14-50 is a 40A circuit because that socket is used in 40A circuits, since 40A sockets are not made). On travel units, use an approved dongle plug since it has the microchip which advertises the available amps.

Note that per Code and UL standards, EVs actually charge at 80% of the breaker/socket/circuit amp limit. So an EVSE that thinks it's on a 40A circuit will tell the car to charge at 32A. That is probably what you have been doing. Breakers have some slack, or you may have a defective breaker (Zinsco, FPE, Challenger).

Use EV's ability to electronically stop load.

You may have noticed when you interrupt large 20A+ loads, there is a GIANT BLUE ARC that jumps across the plug as you disconnect it. This is mildly bad as it creates arc damage on the connector or switch.

You may also notice that if your car is charging and you push the button and pull the charging socket out of the car, NO BLUE ARC. Why is that? Because when you push the button, the car knows it, and immediately suspends charge electronically so by the time you pull it out, 0 amps is going across it.

This is not your father's battery charging tech.

The car will also suspend charge electronically if you tell it to stop charging in its console or at the EVSE. (the EVSE will remove the "authorized to draw power" signal, and the car will stop charging.)

So one should never use a circuit breaker to do a hard cut of charging power, unless there is a problem. Use whatever connectivity options your car or EVSE provide and tell it to suspend charging.

If the EVSE is definitely unplugged and not drawing, I don't see a problem cutting at the breaker, but they have limited cycles. Except.

Getting breakers rated for that, though.

The big blue arc will wear out breakers just like any other switching equipment. Normal breakers are not rated for this duty.

However, they make breakers which are, called "SWD" or Switching Duty". In commercial or industrial spaces (e.g. CostCo) they often control the lights directly at the circuit breakers and don't bother having normal switches. They use special SWD breakers for this duty. This is on lighting circuits ranging from 15 to 30 amps, single-phase 1-pole.

When UL found the manufacturing cost difference in SWD vs non-SWD breakers is negligible, they mandated all 15-30A single-pole breakers be SWD.

That rule does not apply to 2-pole breakers because they're not used for lighting.

"Hey. I'm aware of a product called a handle-tie that can tie two single breakers together to make a double. Can I grab two 1-pole 30A's that are SWD, and tie them to feed a 240V EVSE?" Not with a NEMA 14- socket, because that has neutral, and with neutral involved a problem on one pole needs to trip both -- common trip. Handle-ties do not provide that (really), it only comes from factory made 2-pole breakers via an internal mechanism. (European DIN rail breakers can field-install that mechanism). If you change to a NEMA 6-xx socket which does not have neutral, then you can use two SWD breakers with a handle tie.

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    @milesmeow edited, but honestly. You have 5k rep here, so not a rank novice. It short-circuits my brain that you care about details like cutting a breaker on an unused EVSE daily, yet being completely blasé to the actively dangerous stuff. Sorry I know you didn't come here for a panel review but holy smoke, literally. Commented Dec 20, 2022 at 19:46
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    @Harper-ReinstateMonica where is the danger? Sure, the socket is wrong. But if the wiring is 30A and so is the breaker, the worst thing to happen is nuisance tripping when something using the socket inevitably draws too much current, isn't it? It is not up to code, but I'm simply not seeing the danger here.
    – jaskij
    Commented Dec 20, 2022 at 21:11
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    @jaskij the danger is in shortcutting generally and getting blind-sided by something you did not think about. Everybody thinks they're smarter than the teams of EEs that write the Code... but they're not. People who do not do risk analysis for a living are stupendously bad at it. They focus on what they know about and ignore what they don't know about. They know about airplane crashes because they make the news, so they drive footloose to the airport then need dramamine to get on a plane. Commented Dec 20, 2022 at 21:15
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    @jaskij the worst thing is breaker not tripping, because it is defective or load is just low enough to not trip immideately and just high enough to start damaging the wires. Which is Harpers suspicion is correct, might actually happen. Commented Dec 20, 2022 at 21:19
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    EV charging is basically the highest type of load possible at a residential. Not even heaters and ovens do this because they power cycle to maintain temperature.
    – Nelson
    Commented Dec 21, 2022 at 3:21
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This is generally correct. The question is one of what you want to do about it.

Many business owners just accept that using a breaker as a switch means they're going to have to replace it periodically.

Installing a real switch rated for that power might be the wiser choice, if you don't already have an electrician on staff.

Is there no power switch on the mobile charger itself?

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    "replace it periodically" => keep at least one spare in stock, at least for essential items. Commented Dec 20, 2022 at 18:44
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    The SWD rated breakers are made for that duty and are trouble-free. Available only in a few sizes, but in those sizes they are the default. Try to find a 120V/20A breaker that isn't SWD lol. Commented Dec 20, 2022 at 21:11
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    Interesting. Are SWD breakers available in all brands/configurations? I haven't seen explicit mention of that in the breakers I've purchased, but I admit I didn't have reason to go looking.
    – keshlam
    Commented Dec 20, 2022 at 22:13
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    There’s no switch in the mobile charger. It is always powered on. I guess I can just leave it plugged in and it will just draw some power.
    – milesmeow
    Commented Dec 24, 2022 at 17:12
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    A charger draws very little power when not in use -- probably not much more than your phone chargers or other home electronics with a stand-ny mode. Even if you're pushing towards maximum efficiency, you can probably get the same gain more easily elsewhere.
    – keshlam
    Commented Dec 24, 2022 at 17:26
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To answer your question: yes, this is bad.

As you pointed out, breakers are not switches. They're circuit breakers. They're over-limit protection devices, which is approximately analogous to emergency devices. Think of what you're doing as using a dedicated emergency exit as a normal ingress.

Over time, your circuit breaker will wear out. More than likely, it will just stop completing the circuit during normal operation. There's a small chance that it will fail to stop overcurrent as a failure condition, but this could be considered a general overall failure.

Don't listen to whoever said to prefer the breaker to wear out over the plug. This is incorrect. A plug/socket pair is (always) designed for more open-close cycles than an over-limit protector, in the same circuit. This is because plugs are meant to be plugged into and unplugged from sockets.

You have researched the expected lifetime of this breaker, about 5,000 cycles. I did some research and couldn't find the expected cycle lifetime count for a plug. What I did find a lot of was lifetime warranties. The manufacturer of the breaker tells you that you may switch it 5,000 times. The manufacturer of the plug says you can use it as much as you like, and they'll replace it if it wears out. It seems logical to me that the former isn't meant to be used repeatedly while the latter is.

Your best solution, if you will not unplug this, is to install another device, a switch, in the circuit. Please use a UL-listed switch that's rated for running at 50A.

Also, please run a proper 50A circuit to drive your 50A circuit. While the breaker is listed for 30A, ordinary breakers are not guaranteed to trip until 1.5x the current, 45A in your case. You'd need #6 wire to carry this current.

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  • Your suggestion of #6 wire ignores duty cycle and thermal ratings of the wire and length.
    – agone
    Commented Dec 22, 2022 at 20:53
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    Many breakers explicitly are switches ("switch duty" rated).
    – nobody
    Commented Dec 22, 2022 at 23:59

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