40 amp charging on 8 awg copper.

[RLXXI]

Quick google search of how a circuit breaker works says it uses the heat from over current across a metal strip in the breaker to trip it. Ie if the breaker over heats it trips.
“A circuit breaker works by using a thermal-magnetic trip unit to automatically interrupt the flow of electricity when an electrical fault, such as an overload or short circuit, occurs. For overloads, a bimetallic strip heats up, bends, and trips the breaker, while for short circuits, a powerful electromagnetic force pulls the switch to disconnect the circuit. “

The heat is caused by excessive current flow that trips it. It won't get hot if the correct amount of current is being used. Using an inferior made breaker that can't handle the current they assign it Eg: Using a .02 thick contact when it should have a .12 thick contact. (<-- arbitrary numbers for example not specific). Will cause excess heat that Won't trip the breaker, instead it melts things.

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[Henry Ford]

Code (properly sized wiring and breaker) is written to prevent the wires in your walls from burning your house down. Once the wires are outside of the walls it's on the user to not burn their house down.

A 40A charger should NOT be used on a 40A circuit under ANY circumstances.

@Rtashiro, the reason your outlet melted is because you overloaded the circuit. You should not run more than 32A continuous on a 40A circuit. If you continue to run a 40A charger you risk burning your house down. Don't overthink it.

 

[Rtashiro]

Code (properly sized wiring and breaker) is written to prevent the wires in your walls from burning your house down. Once the wires are outside of the walls it's on the user to not burn their house down.

A 40A charger should NOT be used on a 40A circuit under ANY circumstances.

@Rtashiro, the reason your outlet melted is because you overloaded the circuit. You should not run more than 32A continuous on a 40A circuit. If you continue to run a 40A charger you risk burning your house down. Don't overthink it.

I understand what you are saying but what I am saying is that the wire is rated for 40 amps continuous or 55 amps max. The plug melted because it was a $5 stove plug making bad contact. The wires themselves have no sign of overheating after close to 3 years of use.

 

[Rtashiro]

I just googled wire gauge for 40 amps continuous evse and it is saying 8awg wire on a 50 amp breaker but when I google if you can run 8awg wire on a 50 amp breaker it says no. This is the confusion I’m having.

 

[Heliian]

I just googled wire gauge for 40 amps continuous evse and it is saying 8awg wire on a 50 amp breaker but when I google if you can run 8awg wire on a 50 amp breaker it says no. This is the confusion I’m having.

No confusion, the cec differs from the nec. Most people don't know the actual current codes either. Your electrician should, talk to them.

 

[Henry Ford]

I just googled wire gauge for 40 amps continuous evse and it is saying 8awg wire on a 50 amp breaker but when I google if you can run 8awg wire on a 50 amp breaker it says no. This is the confusion I’m having.

What kind of wire is it? Romex? THHN?

 

[Rtashiro]

What kind of wire is it? Romex? THHN?

Teck 8/3 copper conductor. Teck 1 kv teck90 rated for 90 degrees c wet or dry. Ampacity 55 amps at 90 degrees c

 

[Henry Ford]

I understand what you are saying but what I am saying is that the wire is rated for 40 amps continuous or 55 amps max. The plug melted because it was a $5 stove plug making bad contact. The wires themselves have no sign of overheating after close to 3 years of use.

You are looking for reasons to keep doing what you are doing.

I cannot find anything that says 8awg is appropriate for a 50A circuit. A 40A circuit should use a minimum of 8awg and shouldn't have a load of more than 32A continuous.

You will melt another outlet if you keep doing what you are doing.

 

[Rtashiro]

You are looking for reasons to keep doing what you are doing.

I cannot find anything that says 8awg is appropriate for a 50A circuit. A 40A circuit should use a minimum of 8awg and shouldn't have a load of more than 32A continuous.

You will melt another outlet if you keep doing what you are doing.

I know why the plug was over heating. It was a junk plug. The proper plug is not even warm whereas the plug was hot to the touch when charging before. There is plenty online about using a heavy duty plug for evse’s.

 

[Rtashiro]

I know why the plug was over heating. It was a junk plug. The proper plug is not even warm whereas the plug was hot to the touch when charging before. There is plenty online about using a heavy duty plug for evse’s.

Link here

 

[RickKeen]

AI is never wrong...

 

[Rtashiro]

AI is never wrong...

The link above is for a website lectrium that advises on evse installation. That is just the screenshot of the section that says 8awg is safe for 40 amps continuous charging but not 48 amp.

 

[Henry Ford]

I know why the plug was over heating. It was a junk plug. The proper plug is not even warm whereas the plug was hot to the touch when charging before. There is plenty online about using a heavy duty plug for evse’s.

How many heat cycles did the old outlet have before it failed? How many heat cycles has the new outlet had?

You are literally playing with fire. Is it worth the extra 1.9kW?

 

[Rtashiro]

I do agree to be 100% safe I think I should dial down to 32 amps which is really disappointing. It’s only 8 amps but the grizzle e duo charger I’m using charges at only 24 amps when a second vehicle is plugged in as it reserves 8 amps for the non charging vehicle. Whereas if it is set to 40 amps it gives 32 amps to the one charging and only gives 40 when both cars are charging (50/50) or only one vehicle plugged in. 40 amp draw is almost never over 3 hrs but I guess the potential is there.

 

[P-38]

Alright...first I am not an electrician so I am not 100% up on NEC and it seems like OP is in Canada so code things can be different. I am an electrical engineer and do size wires.

8 awg is fine for a 50 amp circuit. The issue is what type of wire insulation.

NM-B. AKA Romex. Because the sheath keeps everything together and what the sheath is made of the code makers only want to allow the conductor temperature to reach 60 C under full load(40 amps per the table). Conductor temperature meaning the temperature of the copper, not the insulation, the insulation will feel fine.

THWN or any type of insulation from the 2nd column the code makers decided it can get to 75 C without degrading the insulation or allowing too much heat to enter the surrounding area and therefore carry 50 amps.

THHN or anything in the 3rd column. 8AWG is good to 55 amps because the insulation can handle higher temperature. While one might think they can put a 60 amp breaker on 8 AWG (using the next size up standard breaker size from the wire ampacity), in general practice you cannot because the breaker and probably the outlet are only rated for the lugs to reach 75 C. Thus since you have to size to the lowest temperature of the items in the circuit you end up at 50 amps.

So if I were installing a 40 amp EVSE I would use 8 AWG THHN in ENT on a 50 amp breaker assuming the run was short enough that the voltage drop is not a concern and that it is not in an environment that is really hot(such as a steel plant that has a high ambient temperature).

It could be that a breaker and outlet combo exists such that they are rated to 90 C and then you could use a 60 amp breaker. Generally in the US the 90 C column is used for a starting point when derating for conduit fill.

There are a whole lot of details that go into getting this stuff right so you don't have problems (fire, excess voltage drop, internet forum crucifixion...)

I don't know the rules in Canada. It could be that they feel a 60 amp breaker is fine as the wire can handle it if you let the copper get to 90 C.

I'm also sure I missed a detail or an exception that would allow higher amps.

I am sure a 40 amp EVSE on a 50 amp breaker with 8 AWG column 2 or 3 insulation type, correctly installed and protected is allowed by NEC and is a fine way to install an EVSE.

I am equally sure some inspectors would not allow it.

And now I wait to be branded a heretic who is burning down innocent people's homes.

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