Welcome to Tesla Motors Club
Discuss Tesla's Model S, Model 3, Model X, Model Y, Cybertruck, Roadster and More.
Register

Max charging amp on 240v60a circuit without wall charger

kishkaru

Member
Feb 3, 2020
217
215
The Bay, CA
NEC does not care about the length of wire. It's the same requirements if it's 1 ft or 100 ft. The rating is for current and is a constant.
Now, you can voluntarily upsize the wire to reduce voltage drop for a long run, but that's your call. NEC doesn't care about voltage (0-2kV) or voltage drop, but it is recommended to keep it < 2% under load if possible (235V).

However, don't forget to take into account ambient temp correction factor if in a warm environment (e.g. garage or attic). The NEC is based on a strict 30°C (86°F). This is especially important if using NM-B (Romex) wire which fall under the 60°C wire rating. The correction factor for those is very restrictive.
 
Last edited:

Rocky_H

Well-Known Member
Feb 19, 2015
6,445
7,675
Boise, ID
Looking at the chart here for amp and wire length, it looks like 6ga is even overkill for a 48 amp draw since my wire length is about two feet.
That chart is downright disturbing. It shows 10 gauge wire being acceptable on a 50A circuit, which is wrong and dangerous. And for another factor, what size wire you need depends on what type of wire it is and the installation method. If it is individual wires pulled through conduit, that has a different amps allowed for the gauge size than if it is the bundled multi-wire cable in the rubber sheath being run directly inside insulated walls. That is called Romex or NM-B. And I don't think I've seen you mention which way your install is. Try this chart:


The first column is for the Romex cable in walls, where you can see the max allowed amp circuit size per gauge, and the second column is for the wires in conduit.
 
  • Like
Reactions: davenlei

jcanoe

Active Member
Oct 2, 2020
2,710
2,662
Maryland
I am planning on getting a second Tesla in the near future and heard that 'dual' charging with the wall charger would be activated sometime in the future.
When I had this 14-50 circuit installed a couple months ago, the electrician said I only needed 8ga wire for the 50 amp circuit since the length of the run is so short. I insisted he put in 6ga wire because I told him I was likely going to go with the wall charger for the dual charge capability in the future and only wanted to have to install the wall charger and change the circuit breaker from 50A to 60A which is super easy. I was just concerned if I needed to go to 4ga for the wall charger or not if drawing the full 48A. I don't want to get the 4ga wire if that is excessive and pointless from a safety standpoint.

Looking at the chart here for amp and wire length, it looks like 6ga is even overkill for a 48 amp draw since my wire length is about two feet.

I would not use that table as a reference. I always refer to the Cerro Wire Ampacity Charts: Ampacity Charts - Cerrowire

Since your service panel is located in the garage it might make sense to just install a second charging circuit and forget about the Tesla load sharing feature. You could install two Wall Connector units, each on a 50A circuit (the way the current receptacle is setup.) Alternately, depending on the daily charging needs of each driver, perhaps only one of the charging circuits needs to be 50A and the second charging circuit could be 40A or 30A or even 20A so as to not overload the panel. In practice any of the 240V - 20/30/40/50/60 charging circuits is going to enable you to add at least 100 miles or more of driving range to the Tesla Model Y over 8 or more hours of overnight charging. If I had to pick one, or two charging circuit ratings these would be either the 50A or the 40A. With two charging circuits these don't have to have the same circuit rating, especially if one vehicle is driven 30 miles per day or less.
 

davenlei

Member
Feb 16, 2021
46
9
Orange County, CA
Thank you guys for the detailed response and also identifying the reference chart I found is totally wrong. I considered adding another circuit when I get another Tesla but I only have two spaces left on the panel and adding another EV circuit will fill my panel and not allow me to add anything else in the future without adding a sub panel which I want to avoid if possible. Maybe I can swap out some of the existing smaller amp breakers with the slim units so two circuits will fit into the space of one.
Hmm.. I will just talk to my electrician when I get closer to needing to find a solution.
 

Rocky_H

Well-Known Member
Feb 19, 2015
6,445
7,675
Boise, ID
Thank you guys for the detailed response and also identifying the reference chart I found is totally wrong. I considered adding another circuit when I get another Tesla but I only have two spaces left on the panel and adding another EV circuit will fill my panel and not allow me to add anything else in the future without adding a sub panel which I want to avoid if possible. Maybe I can swap out some of the existing smaller amp breakers with the slim units so two circuits will fit into the space of one.
Hmm.. I will just talk to my electrician when I get closer to needing to find a solution.
I think the thing that messes people up on this is getting the process backward. They go in with telling the electrician, "I need a XX size circuit." And then when the electrician does the calculations and looks at your panel, sometimes that is "Well, it would take all this to make that happen." (EXPENSIVE) Frequently, you are better off going in with a question, "What size circuit could I add to my system?" And maybe that's a little lower than you were intending but could save thousands in service upgrades and panel replacements. A 30 or 40A circuit is still very solid, and if that can be done cheaply, but a 50 or 60A crosses some threshold in the load calculation, you might be fine to take what is a bit simpler.
 
  • Informative
Reactions: jjrandorin

MD-2000

Member
May 1, 2019
586
402
Winnipeg
Don't be silly; of course it is fine stranded wire. Anything above Class B is considered fine stranded wire. Probably Class K wiring in that appliance cord.
7 strands seems about right, without opening the thing back up to have a look. So... class B. rated for 50A, with 6Ga for power lines, 8Ga for ground and neutral.

I am planning on getting a second Tesla in the near future and heard that 'dual' charging with the wall charger would be activated sometime in the future.
The manual for the Wall Charger install explains how to wire up the communications between 2 wall chargers so they share a circuit and take turns. There's nothing I saw in that manual that suggested it was a not yet implemented "future feature"... (sort of "Full Self Charging"?) But I assume it was something like A charges to completion, then B will start charging when A is done, not a situation where each takes turns charging for an hour back and forth.

As for correct gauge, that can vary by state or province. Check your local code. When I bought a wall charger to replace the portable, I upped the breaker from 40A to 50A and to be safe, had the wire replaced 8Ga with 6Ga so I could draw 40A continuous. I've seen charts that say 8Ga should have been fine, and others that said I should use 4Ga (Yikes!!) but locally, the electrician who installed it said the standard was 6Ga.
 

jcanoe

Active Member
Oct 2, 2020
2,710
2,662
Maryland
7 strands seems about right, without opening the thing back up to have a look. So... class B. rated for 50A, with 6Ga for power lines, 8Ga for ground and neutral.


The manual for the Wall Charger install explains how to wire up the communications between 2 wall chargers so they share a circuit and take turns. There's nothing I saw in that manual that suggested it was a not yet implemented "future feature"... (sort of "Full Self Charging"?) But I assume it was something like A charges to completion, then B will start charging when A is done, not a situation where each takes turns charging for an hour back and forth.

As for correct gauge, that can vary by state or province. Check your local code. When I bought a wall charger to replace the portable, I upped the breaker from 40A to 50A and to be safe, had the wire replaced 8Ga with 6Ga so I could draw 40A continuous. I've seen charts that say 8Ga should have been fine, and others that said I should use 4Ga (Yikes!!) but locally, the electrician who installed it said the standard was 6Ga.
The Gen3 Wall Connector supports load balancing so that up to four Gen3 Wall Connectors can be connected to a single circuit (up to 100A.) Each Gen3 Wall Connector will still be limited to maximum of 48A. Unlike the Gen2 Wall Connector the Gen3 Wall Connector does not need additional signaling cable to be installed between the Wall Connector units to utilize the load balancing feature as this is done using WiFi. Load balancing will automatically limit the maximum amperage of each Wall Connector when two or more Wall Connectors are in use at the same time. I.e., when there are (2) vehicles charging at the same time on a single 60A circuit the maximum charging amperage for the circuit remains 48A; each Wall Connector will be limited to 24A until one of the two vehicles completes charging. Then the vehicle that is still charging can charge at the full 48A. This happens automatically, no user input required. Some Gen3 Wall Connector customers have reported that Tesla has started field testing (beta testing?) the load balancing feature with the Gen3 Wall Connector. This requires a new version of the Wall Connector firmware to be installed on the Wall Connector units. This firmware is not yet in general release.
 

Rocky_H

Well-Known Member
Feb 19, 2015
6,445
7,675
Boise, ID
There's nothing I saw in that manual that suggested it was a not yet implemented "future feature"...
Exactly! That's what was so damn infuriating about it! Tesla replaced the Gen2, which had this feature, with the Gen3, which DIDN'T have it, but listed the functionality in the manual as if it already did. It's been over a year that people have been waiting for this to be created by Tesla, and is one of the really bad cluster#$%s that Tesla has done.

As @jcanoe mentioned, it was just yesterday that we saw posts on this forum that Tesla has sent a firmware with this feature to a few electricians to try out, but it's still not publicly deployed yet.
 

MorrisonHiker

S 100D 2021.12.25.7
Mar 8, 2015
9,857
9,222
Colorado
Exactly! That's what was so damn infuriating about it! Tesla replaced the Gen2, which had this feature, with the Gen3, which DIDN'T have it, but listed the functionality in the manual as if it already did. It's been over a year that people have been waiting for this to be created by Tesla, and is one of the really bad cluster#$%s that Tesla has done.

As @jcanoe mentioned, it was just yesterday that we saw posts on this forum that Tesla has sent a firmware with this feature to a few electricians to try out, but it's still not publicly deployed yet.
We have a friend who received the update with load sharing for one of his gen 3 wall connectors over a week ago. I haven't heard if his other wall connector ever got the update. I'll reach out and see if he has gotten load sharing working.
 

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