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Actually, it is the voltage. Killing a human requires only 10-50mA, which translates to ~50V with a typical resistance of the human body of ~1kΩ.You can safely touch both poles of a (12V) car battery - which can deliver way more than 50A - without any problems.
I respectfully disagree. You can get hit with 1 million volts and if the amps are low you'll survive. But 50 amps even at low voltage will do you in. I like to think of volts as the height of a waterfall and amps as the volume of water coming over that waterfall. A dribble coming from a high waterfall won't really hurt that bad. But Niagara falls will kill you.

I wouldn't recommend (un-)plugging that circuit under load, though, to not fry the contacts. Make sure charging has stopped in the car first, no need to throw the breaker then. When throwing the breaker while charging repeatedly, its contacts might fry over time.
You should always make sure charging has stopped first, and then first unplug from the car. But the outlet is still hot, and it's still recommended to throw the breaker before unplugging the EVSE.

I'm not in anyway diminishing the value of plugin EVSEs -- I own one! But in the 5 years I've had it, I've unplugged it maybe 3 times. It essentially acts as a hardwired connection as it should be given the electrical load. I only bought a plugin because I plan to take it with me if I move. Otherwise the connection is permanent.
 

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Clipper Creek is one of the premier EVSE manufacturers, and they make high-amperage plug-in models. Here is an excerpt from their manual:

240V plugs are specifically designed for occasional relocation, such as moving from one home to another home.
• For personal safety, the circuit breaker MUST be turned off prior to plugging in AND/OR unplugging 240V appliances (including this EVSE).
• A dedicated NEMA outlet (receptacle) is highly
recommended. NEMA outlets wear out over time particularly when repeated insertion and removal of NEMA
plugs occur. Check the receptacle to be sure it is not worn. A
worn receptacle can cause the plug connection to overheat
and become a fire hazard. Do not use a plug that gets
excessively hot. It is recommended that plug-in EVSE
remain plugged in.
 

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I respectfully disagree. You can get hit with 1 million volts and if the amps are low you'll survive. But 50 amps even at low voltage will do you in.
A car battery is typically 60-85 amps, and low voltage, so I respectfully disagree ;)

You need both high enough voltage to get through the resistance of the skin and enough amps to do damage for it to be dangerous. As someone said, volts hurts, amps kills.
 

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A car battery is typically 60-85 amps, and low voltage, so I respectfully disagree ;)

You need both high enough voltage to get through the resistance of the skin and enough amps to do damage for it to be dangerous. As someone said, volts hurts, amps kills.
I was watching this from the sidelines for a while, but now I can't resist jumping into the fray... 🤓

First off, while one could argue that most of your various statements are equivalent to one another (because of how voltage and current are related via Ohm's law), I would personally never say that a battery has a certain number of amps. A battery has a voltage and an (internal) resistance. When you short out the battery, the only resistance in the circuit is the battery's internal resistance. Divide the voltage by that resistance - and voila - you get the maximum amperage that this battery can produce. However, notice that under that scenario there is no useful work being performed at all - the battery will just heat up (very rapidly, usually with bad outcomes).
Normally your circuit contains some useful load - some consuming device - with a resistance that is hopefully significantly higher than the battery's internal resistance. Since voltage drop is proportional to resistance, this means that most of the battery's voltage goes to the consumer, and very little of it is used to heat up the battery itself.

With this out of the way, let's come back to what really started this whole discussion - the act of unplugging a nema 14-50 outlet. Here is what's going on:

When you plug the car into the circuit, the car represents the load. If your energy source presents 240 V across its terminals, and if your car makes use of that by charging at 40 amps, then this means that the car (ignoring internal resistance of the source) at that point in time represents 240 / 40 = 6 Ohms of resistance. (Back-of-the-envelope calculation. The reality is a bit more complex than that, having AC rather than DC, and so forth.)

When the car stops charging, it represents (for all practical purposes) infinite Ohms, so the current goes to 240 / infinity = 0 amps. At that point, when you unplug your outlet, you introduce another resistance into the circuit. Consider the moment just a tiny fraction of a second after when the plug's and the outlet's terminals first separate, making a tiny air gap. At that moment the resistance across this gap is suddenly quite high - but it is still dwarfed by the (infinite) resistance of the (currently not charging) car. So some small voltage drop appears at the air gap, but it is too small to do anything. Once the plug has moved away from the outlet, things are safe.

If you do the same thing while the car is charging, then the situation is quite different: Plug and outlet form their tiny air gap - which has a much higher resistance than those 6 Ohms of the car. Since the voltage drop is proportional to the resistance, almost all of the total 240 V of the source are now present at that tiny air gap. That is enough for electrons to jump across the gap, ionizing the air molecules, and creating an electric arc. This arc is what's the problem - it heats things up, wears out outlets and possibly plugs, and can be a fire hazard.

So, in short, it is safe to unplug while the car is not charging. It is not safe to do so while it is charging.
(Of course, there is also the mechanical wear-and-tear on the outlet, which is a separate issue.)

Some here have suggested first throwing the circuit breaker before unplugging. By the above analysis this seems unnecessary if the car is not charging. But that could be a big "if": If the car decides, unbeknownst to you, that it wants to charge after all just before you pull the plug, then you'll have a nice big electric arc going on.
Circuit breakers have the same problem - they also open the circuit. However, they are specifically designed to handle this sort of arcing since they are meant to open when the current is very high. So to be on the very safe side, indeed, throw the circuit breaker before unplugging.

The other option, of course, is to unplug the cable from the car first. This connection is also specifically designed to prevent arcing at the plug itself: The plug is locked, and you first have to "tell" the car by pressing the button that you are about to disconnect. This causes it to make absolutely sure it is not charging before it unlocks the plug so that it can then be removed safely. Once the car side is disconnected, unplugging from the outlet should be (almost (*)) completely safe.

None of this has (or should have) anything to do with whether or not the voltage in question is safe to be applied to the human body. Hopefully your fingers and other body parts are well away from the metal bits and pieces when you unplug. 😜

By the way, it is power that kills. Power is voltage times amperage. Or amperage squared times resistance. Or voltage squared divided by resistance. (Aside from that, AC can also kill in other ways. 50 or 60 Hz can mess with a human's heart rhythm quite badly.)

(*) The charging cable has circuitry built-in, so it does not actually have infinite resistance. But the actual resistance is still high enough to prevent significant arcing at the plug.
 

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Excellent explanation, thank you.

I can't resist
You mean your resistance dropped 😆

Some here have suggested first throwing the circuit breaker before unplugging. By the above analysis this seems unnecessary if the car is not charging. But that could be a big "if": If the car decides, unbeknownst to you, that it wants to charge after all just before you pull the plug, then you'll have a nice big electric arc going on.
As to this "if", the P2 is somewhat notorious for waking up when you least expect it. It seems that all you have to do is breath on it and it starts charging again.
 

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I’m not going to touch any battery that’s for sure. The contractor will install a commercial grade plug with a switch in the box. I’m gonna put a little white board next to it and tic off the plug in cycles. Also, I always stop the charge at the car first.
 

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I’m gonna put a little white board next to it and tic off the plug in cycles.
This might be a little overkill, but I get your point. :D
You'll start to know if you are unplugging too many times.

with a switch in the box.
This is a great idea. He can put a breaker right next to the outlet so you don't have to go back to the fuse box.
 
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