How does the Receptacle , the wiring, CB and code Relate?

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Jadnashua

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If I understand it correctly, you should not use a 20A receptacle on a 15A circuit ? But, what about say a dryer circuit that has a 50A receptacle...If what you intend to plug in there only calls for say 40A, would it be okay to use wiring and a 40A CB, or, does code require it to support 50A because the receptacle will allow some other device that may need that amount of power? If the thing required 50A, and the wiring and CB were 40A rated, you probably wouldn't burn anything down and the CB would eventually trip, but does that meet code?

Question comes up, and I know manufacturer's instructions must be followed, too, if you have say an EVSE rated at 32A, but comes with a 50A plug on it...what must the wiring and receptacle be rated at?

Some manufacturers call for a 50A circuit when there's a plug involved, buying the same unit, 40A if hardwired. Some don't specify, but say it must be installed by a licensed electrician. What does the code say about this situation?
 
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I can install a heat pump off a dryer's wire, but not the other way around.

Consider NEMA5-15 used for small window air conditoners that pull about 5A. It's not like we're going to purpoely use smaller than 14Ga just because we know that outlet will be for a small air conditioner. We have to prep that wire for 15A using 14Ga. Likewise we can have a circuit all NEMA5-20 outlets, but I can still plug the small air conditioner into it. Then there is the strange case where we can snap in a 10A CB into that wire, but the wire is still 14Ga rated for 15A.

Your EVSE may draw 32A max, but if it's on a 50A plug, it's going to want a 50A CB on it as well. You can snap a 40A CB on that, but the wire still needs to be 8Ga. or 6Ga., whatever the manufacturer calls for. Your situation is similiar old-fashion one, where a welding enthusiatsts would install wire just to run their electric welders.

You also have to consider we are in a bit of new frontiers here... we may use our stoves and dryers for about an hour max, but you're talking about leaving a car that can potentially draw 32A for very many hours, every single day. We haven't had any newsworthy incidents yet, but if something were to go wrong, it is a lot of juice to make a mess out of.

I were to install something for a EVSE, I'd be using BX armored cable, just because I love my home so much I don't want it to ever burn down.
 

Reach4

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Says who?
Table 210.21(B)(3)
70CCS.jpg
 
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Says who? The circuit breaker protects the wiring and equipment after it. It does not, nor is it intended to protect the appliance or device connected to it.
It would be incorrect to have NEMA5-20 outlets on 14Ga wire, with a 15A CB snapped into the box.

The issue is that the appliance may stress the CB from continuous high amperage use, create excessive heat, and trip the breaker excessively, and this does put mechanical wear and tear on the CB.

There's also the assumption the installed 14Ga wire in the walls are actually still "good". Consider the homeowner of a house built in the 1950s, and all they did was swap out their old NEMA5-15 outlets for 20A ones so they can plug in lamps for their greenhouse "grow-op".
 

DonL

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Question comes up, and I know manufacturer's instructions must be followed, too, if you have say an EVSE rated at 32A, but comes with a 50A plug on it...what must the wiring and receptacle be rated at?

You answered your own question.

If it comes with a 50A plug on it, You need the correct receptacle to plug it into.

The receptacle / breaker and wire going to it must be rated properly.

Is this a test ? :eek:
 

Jadnashua

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FWIW, I do own an EV and have an EVSE installed. On this particular brand, the instructions say if you hardwire it, a 40A circuit is fine, but if you put a plug on it, it must be a 50A circuit. But, the table from the code shown above says you can use either a 40A OR a 50A circuit with a 50A receptacle. But, not all installation instructions specify that. The code lists various types of equipment that can require you to go one way or the other, but does not say anything about an EVSE that I could find.

If you can't install a 20A receptacle on a 15A breaker, why do they allow a 50A one a 40A circuit? What am I missing, or what am I overlooking, if anything?

Code says that on a lighting circuit, it shouldn't be loaded past 50%, but a continuous use, dedicated circuit can be 80% max. I'm not sure why the distinction, either.

In the case of my EVSE, the manufacturer's instructions trump the code, but on identically sized units from other manufacturers, they don't list it.
 
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Hardwired, it has maximum copper contact surface with screws, knives, whatever fastens copper down. So you can hardwire your EVSE to a 40A circuit.

An outlet will have less surface area contact, which is why it wants a 50A plug which MUST ALSO be on a 50A circuit. We're over compensating for that. We're at the mercy of prongs and dirt and oxidation that can come on it over time.

This is exactly why some really large 240V window air conditioners (like 18000BTU and up) don't have a plug option. They must be hardwired. If the technician cheats and tries to install a plug on the appliance, the plug prongs will burn out.

Look it's your home, if you can get away doing whatever you want, and no one will inspect your work, and your home insurance policy don't care, I'm 75% sure that your idea would probably work out for your EV.
2761d1144738995-dryer-240-burnt-plug-plug-18x18.jpg
 
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DonL

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If you can't install a 20A receptacle on a 15A breaker, why do they allow a 50A one a 40A circuit? What am I missing, or what am I overlooking, if anything?

All you are missing is that the plug will not fit. That is done for good reason.

The ones that will fit are allowed. IE 15 and 20 amp. A 15 amp plug will fit a 20 receptacle, But a 20 will not plug into a 15.

You seem to be over thinking. Or maybe it is just me.

Good Luck.
 
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Jadnashua

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Code allows a 50A receptacle on a 40A circuit. My 32A device, if wired to a plug and on a 40A circuit meets the 80% rule, and is okay, but it has a 50A plug attached (but not it's installation instructions, but that seems to be and exception for other brands).
Say I decide I need a 40A device, plug it in because it has the same plug, but now it no longer abides by the 80% rule, but probably won't trip the breaker. No inspection is required to just plug in a new device, but because the code allowed a 50A receptacle, wired and protected for 40A, it doesn't have the same safety margin. Some EVSE installation instructions call for the wiring to be 50A in this case, regardless, but not all.

My question is why is it allowed in the first place? If you are not allowed to put a 20A receptacle on a circuit wired for 15A, why is it okay to do the same thing for a 50A receptacle wired to a 40A circuit?
 
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Jadnashua

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All you are missing is that the plug will not fit. That is done for good reason.

The ones that will fit are allowed. IE 15 and 20 amp. A 15 amp plug will fit a 20 receptacle, But a 20 will not plug into a 15.

You seem to be over thinking. Or maybe it is just me.

Good Luck.
There are NO 40A plugs, but there are 15 and 20A ones. Code seems to allow a 50A plug to be installed on a 40A circuit, but they won't allow the same type of thing with 15/20A ones. Why?
 

JerryR

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You answered your own question.

If it comes with a 50A plug on it, You need the correct receptacle to plug it into.

The receptacle / breaker and wire going to it must be rated properly.

Is this a test ? :eek:

NEMA 14-50R and 6-50R are used for both 50 amp and 40 amp circuits. There are no 40 AMP receptacles.

Majority of L2 EVSE devices draw max of 32 amp. As explained to me by my electrician, code allows a NEMA 6-50R(no neutral) or 14-50R to be installed with 40 amp wire and breaker. If wired for 40 amp (#8 wire) the breaker needs to be 40 amp.

My kitchen stove has a 14-50R with 50 amp breaker and #6 wire.

I prefer hard wired EVSE over plug in. My Eaton L2 EVSE is hard wired. It's max 30 amp (7.2kW). I wired it with #6 and 40 amp breaker. I went #6 in case some day I need to upgrade to 40 amp EVSE that requires a 50 amp supply all I would need to do is replace the breaker.
 
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JerryR

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There are NO 40A plugs, but there are 15 and 20A ones. Code seems to allow a 50A plug to be installed on a 40A circuit, but they won't allow the same type of thing with 15/20A ones. Why?

Don't know why, but I would also like to know the reasoning.
 

Jadnashua

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When installing a new device, you have to do two things: follow the manufacturer's instructions and follow the codes involved. The particular EVSE that I have specifically calls for a full 50A circuit (wiring and receptacle) when installing one of their 32A devices when supplied with a plug. They specify a 40A breaker and wiring for the same thing hardwired. To me, that makes perfect sense, since if you installed a 40A device on that 40A service, it may not trip, but would not provide the required 125% capacity (80% rule) for a continuous use device like that. FWIW, EVSE = Electric Vehicle Support Equipment (essentially, a smart on/off switch, the charging circuit is in the vehicle). On some EV forums, I've (apparently incorrectly) been pushing to make the circuit 50A to match the receptacle, and the device I have requires that in their instructions, but after I started this thread, I looked at a few more, and some either don't say, or allow it to be a 40A circuit with that 50A receptacle. As I said before, they don't allow that for a 15A circuit, you can't put a 20A receptacle on it, but you can put a 15A one, because the device hooked up to it won't stress the wiring. That is NOT true of a 50A receptacle on a 40A circuit...many people would just see that the thing they want to plug in will fit, and use it.

Now, the code is hundreds of pages with some exceptions to the general rules, so I'm wondering if this has been addressed.

Few EV's out there today draw more than 32A when recharging with an EVSE, so a 40A circuit, even with a bigger device would probably work (but not meet code). This may not be true forever, as battery capacities are increasing, and to get the vehicle recharged in a timely manner, a larger EVSE may become more popular as a DC fast charge is generally out of reach for a homeowner since those can draw over 100A at a supply voltage not commonly available in a home. Those are an actual high voltage power supply, bypassing most of the charging circuits in the car verses an acv input feeding the car's power supply.
 

JWelectric

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Code seems to allow a 50A plug to be installed on a 40A circuit, but they won't allow the same type of thing with 15/20A ones. Why?

It is known as load diversity same reason we are allowed to take only forth percent of our service load for anything over ten KW.
 

DonL

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That is NOT true of a 50A receptacle on a 40A circuit...many people would just see that the thing they want to plug in will fit, and use it.

That is the way it should be.

And the reason the plugs have different blade contacts.

Good Luck.
 
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