40 amp charging on 8 awg copper.

[RickKeen]

If you are wiring with 6AWG NM-B, aka Romex®, then you are correct. 6/3 NM-B is only rated up to 40 amps.

If you are wiring with THHN in conduit, such as FMC, LFMC , EMT, PCV etc then 9 AWG is good for up to 50 amps.

Another mistake people make when wiring 60 amps is using 6 AWG NM-B Romex®. It is only rated for 55 amps. My electrician used 6-6-8 SEU/CU Copper Service Entrance cable to hardwire my 60 amp Tesla charger. It is similar in looks to Romex® but it is rated for 65 amps where similar Romex® is only rated for 55 amps. The difference is that SEU Conductors are annealed (soft), type THHN/THWN copper conductors.

The OP only mentioned 40. amps. I think you are conflating wiring for a 48 amp charger. Yes, for a 48 amp charger, you need wiring sufficient for 60 amps and a 60 amp breaker.

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[Heliian]

If your electrician used nmd90 and its less than 50ft, slap a 50a breaker in.
The american nec allows it too. The internet gets confused with this topic because of the possibility you could have old crappy wiring in your house.

Just confirm with your electrician who knows the cec. He may have only put a 40a breaker in there to save you money, there is quite a price jump from 40 to 50a.

 

[chl]

Hi,

was hoping to get some advice from some experts.
When I got my first Ev (mustang mach e) I hired an electrician to install a NEMA 1450 in my garage. At the time I was using the 30 amp mobile charger but I specifically requested him to install the plug so I could go up to a 40 amp charger in the future. It has worked fine. I eventually got a 40 amp charger which I have used for about a year now and never threw a breaker or anything. From watching YouTube videos I have seen that the cheap 1450 stove plugs are a no no. Sure enough I checked the plug and it was starting to show signs of melting and when it has been charging a while the plug was quite hot. I decided to change the plug out with an Ev rated one. In doing this I see that the wire is 8awg copper which the internet tells me is good for 40 amps continuous which is good. My issue is that he installed a 40 amp breaker. My understanding is that you shouldn’t run the full capacity of your breaker. Then when I looked at upgrading the breaker it said that a 50 amp breaker requires 6awg wire. Is it fine to run the 40 amps as long as it isn’t tripping the breaker? Or am I stuck degrading down to 32 amps? The text cable is mostly running outside. It goes from the panel, straight outside then under a deck to the garage then into the garage. Just want everything to be safe. The wire itself never seemed to be getting any warmer than the charger cord itself.

Yes, generally breakers should not be run over 80% with a continuous load.
(There are specially designed breakers that can run at 100% with a continuous load, but these require ventilation, so not going to work with your typical home panel.)

For a 40A EVSE you need a 50A breaker and at least 8 AWG copper 90 degree wire (for hots, ground can be smaller sized). But if you have a long run, go with 6 AWG to minimize voltage drop and losses.

Go with hard wiring the EVSE, as others have suggested - plugs and receptacles are subject to moisture and resulting corrosion and hot spots. Also if adopted in your area, there is a requirement for the outlet to be GFCI protected, which can cause problems for some EVSEs.

I would also not recommend anyone use the Ford Mobile Power Cord exclusively for charging as there have been several reports of failures, overheating and even partial melting - could be internal issues or the 240V dongle, or corrosion issues.

The above is what the requirements would generally be in the US. However, there are differences in other countries. I believe Canada may have different requirements. Your electrician should be familiar with them if he/she is familiar with EVSE installing.

Always consult the EVSE installation manual for guidance.

---------------
Disclaimer

I am an electrical engineer but not a licensed electrician.

The information provided in this post is provided for information purposes only and does not constitute any endorsement or recommendation. No warranty, expressed or implied, is made regarding the accuracy, adequacy, completeness, legality, reliability, or usefulness of any information found in this post.

It is your responsibility to investigate and verify this information.

 

[Rtashiro]

Yes, generally breakers should not be run over 80% with a continuous load.
(There are specially designed breakers that can run at 100% with a continuous load, but these require ventilation, so not going to work with your typical home panel.)

For a 40A EVSE you need a 50A breaker and at least 8 AWG copper 90 degree wire (for hots, ground can be smaller sized). But if you have a long run, go with 6 AWG to minimize voltage drop and losses.

Go with hard wiring the EVSE, as others have suggested - plugs and receptacles are subject to moisture and resulting corrosion and hot spots. Also if adopted in your area, there is a requirement for the outlet to be GFCI protected, which can cause problems for some EVSEs.

I would also not recommend anyone use the Ford Mobile Power Cord exclusively for charging as there have been several reports of failures, overheating and even partial melting - could be internal issues or the 240V dongle, or corrosion issues.

The above is what the requirements would generally be in the US. However, there are differences in other countries. I believe Canada may have different requirements. Your electrician should be familiar with them if he/she is familiar with EVSE installing.

Always consult the EVSE installation manual for guidance.

---------------
Disclaimer

I am an electrical engineer but not a licensed electrician.

The information provided in this post is provided for information purposes only and does not constitute any endorsement or recommendation. No warranty, expressed or implied, is made regarding the accuracy, adequacy, completeness, legality, reliability, or usefulness of any information found in this post.

It is your responsibility to investigate and verify this information.

This is what I’m reading. I’m reading my local wiring guide and it is saying stove plug NEMA 1450 should be 8awg on a 40 amp breaker. With the proper commercial duty plug I am not getting any abnormal heat now and the wires themselves are only Luke warm after 2 hrs at full load. Breaker is not tripping I think I am going to leave as is for now. I don’t really feel like trashing all that cable and putting out for a new run of 6 awg and a new breaker. If the breaker overheats it should trip anyways which it has not in the 3 years I’ve been running it. I would hard wire but I use the grizzle e duo charger which works really well for my personal situation. Normally only draws the full 40 for short periods anyways seeing as it only draws 49 amps if one car is plugged in or 2 cars are plugged in and charging. If two cars are plugged in but only one charging (which is often) it only draws 32 amps

 

[flyct]

This is what I’m reading. I’m reading my local wiring guide and it is saying stove plug NEMA 1450 should be 8awg on a 40 amp breaker. With the proper commercial duty plug I am not getting any abnormal heat now and the wires themselves are only Luke warm after 2 hrs at full load. Breaker is not tripping I think I am going to leave as is for now. I don’t really feel like trashing all that cable and putting out for a new run of 6 awg and a new breaker. If the breaker overheats it should trip anyways which it has not in the 3 years I’ve been running it. I would hard wire but I use the grizzle e duo charger which works really well for my personal situation. Normally only draws the full 40 for short periods anyways seeing as it only draws 49 amps if one car is plugged in or 2 cars are plugged in and charging. If two cars are plugged in but only one charging (which is often) it only draws 32 amps

What wire is used to your 14-50 receptacle? Is is Romex® or separate wires run in conduit? That makes a difference on the rating!

 

[chl]

This is what I’m reading. I’m reading my local wiring guide and it is saying stove plug NEMA 1450 should be 8awg on a 40 amp breaker. With the proper commercial duty plug I am not getting any abnormal heat now and the wires themselves are only Luke warm after 2 hrs at full load. Breaker is not tripping I think I am going to leave as is for now. I don’t really feel like trashing all that cable and putting out for a new run of 6 awg and a new breaker. If the breaker overheats it should trip anyways which it has not in the 3 years I’ve been running it. I would hard wire but I use the grizzle e duo charger which works really well for my personal situation. Normally only draws the full 40 for short periods anyways seeing as it only draws 49 amps if one car is plugged in or 2 cars are plugged in and charging. If two cars are plugged in but only one charging (which is often) it only draws 32 amps

What size wire and breaker you use depends on the load you are powering.

A 40A continuous load, like an EVSE pulling 40A, should NOT be on a 40A breaker, it should be on a 50A breaker. Fine for 30A or 32A though - which may be what you are actually running?

Some EVSE makers say 40A in advertising but the EVSE really only draws 32A.

The 6 AWG wire was a suggestion for a long run of wire at 40A - wire has resistance and therefor a voltage drop and heat losses can become an issue on a longer run.

Breakers do fail, and if you really are running a continuous load on a breaker at its max rating, it will fail sooner than otherwise. It could also start a fire.

In the US, breakers used for running continuous load are only rated for 80% of their capacity.
It would be a code violation and dangerous to ignore that specification.

 

[Rtashiro]

The ampackfy of the cable is 55 amps which is plenty for 40 amps continuous. The issue is if I want to change to 50 amp breaker I need 6awg wire. Catch 22 I guess. I’m getting 238 volts at the terminals which is fine I’ll read the volts at full load tonight maybe and see

 

[Rtashiro]

What size wire and breaker you use depends on the load you are powering.

A 40A continuous load, like an EVSE pulling 40A, should NOT be on a 40A breaker, it should be on a 50A breaker. Fine for 30A or 32A though - which may be what you are actually running?

Some EVSE makers say 40A in advertising but the EVSE really only draws 32A.

The 6 AWG wire was a suggestion for a long run of wire at 40A - wire has resistance and therefor a voltage drop and heat losses can become an issue on a longer run.

Breakers do fail, and if you really are running a continuous load on a breaker at its max rating, it will fail sooner than otherwise. It could also start a fire.

In the US, breakers used for running continuous load are only rated for 80% of their capacity.
It would be a code violation and dangerous to ignore that specification.

I’m using grizzle e duo charger I can confirm it draws 40 amps at full load

 

[Newton]

A very good discussion here, the only thing that I want to add is that breakers do not prevent fires (at least not in the way that many people assume). If you have undersized wiring or a poor connection, a 40A breaker will happily let 40A of current flow through the wires no matter how hot the wiring is getting. A breaker prevents a short circuit from letting 200A of current flow through wires designed for 20A which would cause the wire to melt and possibly start a fire (although the wire itself acts as a fuse sometimes) but it does not protect against the most common causes of electrical fires. Poor connections/undersized wires have resistance and resistance is how you turn electricity into heat.

/rant

 

[Rtashiro]

I’m also thinking about it more and the breaker trips if it senses circuit overload based on heat to protect the wiring. If it is not tripping it’s not getting hot right?

 

[Rtashiro]

A very good discussion here, the only thing that I want to add is that breakers do not prevent fires (at least not in the way that many people assume). If you have undersized wiring or a poor connection, a 40A breaker will happily let 40A of current flow through the wires no matter how hot the wiring is getting. A breaker prevents a short circuit from letting 200A of current flow through wires designed for 20A which would cause the wire to melt and possibly start a fire (although the wire itself acts as a fuse sometimes) but it does not protect against the most common causes of electrical fires. Poor connections/undersized wires have resistance and resistance is how you turn electricity into heat.

/rant

In my circumstance the wire is sized for 40 amps continuous. Ampacity is 55 amps at 90 c

 

[Maquis]

If your electrician used nmd90 and its less than 50ft, slap a 50a breaker in.
The american nec allows it too. The internet gets confused with this topic because of the possibility you could have old crappy wiring in your house.

Just confirm with your electrician who knows the cec. He may have only put a 40a breaker in there to save you money, there is quite a price jump from 40 to 50a.

The U.S. NEC does not recognize NMD90.

 

[Rtashiro]

Wrong, heat is not a factor for breakers, only current flow. If current flow exceeds it's rating it trips, doesn't matter how hot or cold it is. Never had a fuse melt but not blow in a vehicle? It melted because it's contacts were either dirty, loose, or insufficient material mass for the load applied.

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. “

 

[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.

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