40 amp charging on 8 awg copper.

[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.

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[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.

 

[Rtashiro]

This is the image of the plug I took off that was getting hot. Plug didn’t melt but was getting very hot. Just at the plug. The wire showed no sign of heat on the insulation and this was after 3 years running at 40 amps. There was some damage to the conductor where the original electrician nicked the conductor when he stripped it. I cut off the ends, re stripped it, and fully torqued the lugs on heavy duty plug to 75 inch pounds. Tugged the wires around then re tourqued. No heat whatsoever at 40 amps after several hrs. Of 40 amp draw. No heat on the plug or the conductors.

 

[K6CCC]

Bad job on wiring the plug. Way too much exposed wire on those terminals. And perfectly legal and commonly done, but personal preference is to NEVER use bare wire for ground in a box with exposed terminals.

 

[Rtashiro]

Bad job on wiring the plug. Way too much exposed wire on those terminals. And perfectly legal and commonly done, but personal preference is to NEVER use bare wire for ground in a box with exposed terminals.

yeah I thought the same but the Teck cable has a bare ground. Also I thought the same about too much stripped but when I re stripped I used the strip length gauge on the outlet and it left some exposed copper. I didn’t take a photo of the new plug to compare. The old cheap plug also had pathetic terminals compared to the heavy duty one. If I put 75 inch pounds in the old one I believe it would have broke into a million pieces.

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