Welcome to Tesla Motors Club
Discuss Tesla's Model S, Model 3, Model X, Model Y, Cybertruck, Roadster and More.
Register
  • Want to remove ads? Register an account and login to see fewer ads, and become a Supporting Member to remove almost all ads.
  • The final cut of TMC Podcast #34 is available now with topics timestamped. We covered Tesla's rollercoaster prices, Toyota pushing junk science, Mike's new Model 3, Optimizing track mode for snow driving, FSD V11 apparently coming by the end of this week, and more. You can watch and check out the chat replay on YouTube.

48 Amp Charging Setup Question

Not sure if anyone can answer this question before I do my installation:

I plan on swapping my 50 amp breaker at my main with a 60 amp breaker, I will then have about 20 feet of 6/3 romex going from my main to a 100 amp sub panel. Then from the sub-panel I'll have two 60 amp breakers with #6 THHN going to two chargers.

Does this violate the rule for continuous load?

I know 44A would be the max if I were running it directly from my main but does the sub-panel/THHN change the equation here?

Thanks in advance for any clarity.
 

jcanoe

Well-Known Member
Oct 2, 2020
6,815
7,718
Maryland
This would not be code compliant or safe because you can't use 6 gauge NM-B (Romex) on a circuit rated over 55 amps. To use NM-B it would need to be 4 gauge. You could use 6 gauge THHN.

Assuming that the 2 Wall Connectors will be setup for automatic load balancing then each Wall Connector, alone, would enable charging at 48 amps (80% of 60 amps). When both Wall Connectors were in use they would be limited to 24 amps each. You could set one Wall Connector for a higher maximum amperage but then the other Wall Connector would automatically be limited to a lower limit, i.e. Wall Connector #1 was set to enable charging at 32 amps and Wall Connector #2 would be enabled for charging at up to 16 amps when charging two Tesla vehicles at the same time. As long as together the Wall Connectors do not exceed 48 amps while charging this would be within the 80% limit for a 60 amp circuit.
 
Last edited:
you could also run 3/3 MC cable, which is 3 gauge copper thhn in metal-clad flexible conduit, from your main to your subpanel, on a 100 amp breaker. its an alternative to aluminum SER (service entrance cable), and its advantage is that its in an armored conduit. the SER is half the price, but if its only 20 feet or so the difference is almost meaningless.

your wall connectors could be attached to the sub via 6 gauge thhn or 6 gauge MC (which has thhn inside). both would be able to charge at 48 amps when alone, then 40 amps when sharing.
 
  • Like
Reactions: MacO512
Not sure if anyone can answer this question before I do my installation:

I plan on swapping my 50 amp breaker at my main with a 60 amp breaker, I will then have about 20 feet of 6/3 romex going from my main to a 100 amp sub panel. Then from the sub-panel I'll have two 60 amp breakers with #6 THHN going to two chargers.

Does this violate the rule for continuous load?

I know 44A would be the max if I were running it directly from my main but does the sub-panel/THHN change the equation here?

Thanks in advance for any clarity.
Why not use a local licensed electrician that will file the local permits, arrange for the inspection, and avoid you possibly burning down your house?
 
  • Like
Reactions: rickybobbee

qdeathstar

Completely Serious
May 17, 2019
4,817
4,934
VB
Not sure if anyone can answer this question before I do my installation:

I plan on swapping my 50 amp breaker at my main with a 60 amp breaker, I will then have about 20 feet of 6/3 romex going from my main to a 100 amp sub panel. Then from the sub-panel I'll have two 60 amp breakers with #6 THHN going to two chargers.

Does this violate the rule for continuous load?

I know 44A would be the max if I were running it directly from my main but does the sub-panel/THHN change the equation here?

Thanks in advance for any clarity.

The six three feeding the sub panel limits the breaker in the main panel to 50 amps and limits the maximum continuous load from the subpanel to 40 amps continuous. You can’t run two 60 amp breakers from that sub panel…
 

240vPlug

Active Member
Feb 3, 2021
1,098
779
Maryland
I'm not an electrician but if your running a 100 amp sub panel you need conductor (wire) rated for 100 amps even through you only plan on pulling 48 amps through it. It would also need a 100 amp breaker in the main panel.

Then if your installing two breakers I believe your limited to two 50 amp breakers so your wall connectors would be limited to a max of 40 amps.

What it sounds like your trying to run is a 60 amp sub panel. Two 30 amp breakers and max charge rate of each EVSE would be limited to 24 amps.

If it's only 20 feet why are you running a sub panel? Is your main panel full? I would suggest at least having an electrician come in for a free estimate and tell you what he would do. Then you can decide to do the work yourself if you want.
 
  • Like
Reactions: howardnj
The six three feeding the sub panel limits the breaker in the main panel to 50 amps and limits the maximum continuous load from the subpanel to 40 amps continuous. You can’t run two 60 amp breakers from that sub panel…
I can, I'm not intending on running both and should have clarified that I will be power sharing. 6/3 can handle 44 amps continuous
 
Why not use a local licensed electrician that will file the local permits, arrange for the inspection, and avoid you possibly burning down your house?
Because it's not that difficult of a setup and was seeking advice, I should have clarified that I'll be utilizing powersharing. If anything I'll set the power-sharing to 44 amps and call it a day. Safe for 6/3 romex and won't burn my house down.
 
  • Like
Reactions: fiehlsport
I'm not an electrician but if your running a 100 amp sub panel you need conductor (wire) rated for 100 amps even through you only plan on pulling 48 amps through it. It would also need a 100 amp breaker in the main panel.

Then if your installing two breakers I believe your limited to two 50 amp breakers so your wall connectors would be limited to a max of 40 amps.

What it sounds like your trying to run is a 60 amp sub panel. Two 30 amp breakers and max charge rate of each EVSE would be limited to 24 amps.

If it's only 20 feet why are you running a sub panel? Is your main panel full? I would suggest at least having an electrician come in for a free estimate and tell you what he would do. Then you can decide to do the work yourself if you want.
The 100 amp panel will never see 100 amps as I'll be utilizing powersharing and the most it will ever see is 44 amps which is 80% of the 55 amps 6/3 can handle.
 
This would not be code compliant or safe because you can't use 6 gauge NM-B (Romex) on a circuit rated over 55 amps. To use NM-B it would need to be 4 gauge. You could use 6 gauge THHN.

Assuming that the 2 Wall Connectors will be setup for automatic load balancing then each Wall Connector, alone, would enable charging at 48 amps (80% of 60 amps). When both Wall Connectors were in use they would be limited to 24 amps each. You could set one Wall Connector for a higher maximum amperage but then the other Wall Connector would automatically be limited to a lower limit, i.e. Wall Connector #1 was set to enable charging at 32 amps and Wall Connector #2 would be enabled for charging at up to 16 amps when charging two Tesla vehicles at the same time. As long as together the Wall Connectors do not exceed 48 amps while charging this would be within the 80% limit for a 60 amp circuit.
That was my thought and I'm sorry I didn't clarify that I would be load-sharing. The sub-panel will never see more than 48 amps combined with the load sharing. I was just unsure if it was alright to pull that much with the romex.
 

240vPlug

Active Member
Feb 3, 2021
1,098
779
Maryland
Yes you can as long as I don't pull more than 55 amps. NEC 240.4(B)
Tesla Wall connector manual says if installing for maximum power minimum is #6 90C wire. NM-B is a 90C rated wire....HOWEVER...ampacity of NM-B is limited to 60C so it is 55 amps. It is very confusing for a lot of folks...even electricians. The bigger question I have is why is it rated 90C but limited to 60C ampacity?
 

jcanoe

Well-Known Member
Oct 2, 2020
6,815
7,718
Maryland
Tesla Wall connector manual says if installing for maximum power minimum is #6 90C wire. NM-B is a 90C rated wire....HOWEVER...ampacity of NM-B is limited to 60C so it is 55 amps. It is very confusing for a lot of folks...even electricians. The bigger question I have is why is it rated 90C but limited to 60C ampacity?
NM-B can be run in attics. Depending on the region attic temperatures can be above 60C (140F).
 

iamnid

Active Member
Dec 4, 2019
1,171
1,226
Riverside, CA
You could just limit the wall connector to 40 amps, use a 50 amp breaker, and be fine. I have two places with 2 different wall connectors. One is 40 amps and one is 48 amps. You'd think there'd be a large difference in charge times with that extra 8 amps, but it really isn't that significant.
 

About Us

Formed in 2006, Tesla Motors Club (TMC) was the first independent online Tesla community. Today it remains the largest and most dynamic community of Tesla enthusiasts. Learn more.

Do you value your experience at TMC? Consider becoming a Supporting Member of Tesla Motors Club. As a thank you for your contribution, you'll get nearly no ads in the Community and Groups sections. Additional perks are available depending on the level of contribution. Please visit the Account Upgrades page for more details.


SUPPORT TMC
Top