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Requested 60 amp wall charger install, builder wired 6/3 NM-B. Options?

Does it matter that the on-board charger in the Tesla maxes out at 48A? If there's no possibility to charge over 55A, then why isn't a 6# wire allowe, given the temperature specs also check out?
I went down this road myself :) since they installed Romex 6/2. It's the continuous load rules apparently you should only run at 80% continuous. so 40x1.25 50amp breaker or 48x1.25 for a 60 amp breaker. I'm stuck right now with the Romex so I'm doing 44x1.25 that gives me the rated 55amps on the wire but still not code with my 60 amp breaker. I'm going to replace it with 6/2 THHN MC which is rated to 75amps

Not sure why everyone is in love with their 14-50 outlets chargers don't need that extra wire so 6-50 is fine if you're only using it for EV's. and saves money on wire.
 
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swaltner

Active Member
Oct 13, 2012
1,720
1,834
Kansas, USA
Does it matter that the on-board charger in the Tesla maxes out at 48A? If there's no possibility to charge over 55A, then why isn't a 6# wire allowe, given the temperature specs also check out?
No. That's the whole point of this thread. Look up "continuous load". In regards to the electric code, a continuous load is one that is expected to continue for 3 hours or more. When this is the case, you need to derate the circuit to 80% of the current rating for the wire and break.

15 amp breaker/wire = 12 amp EV charging
20 amp breaker/wire = 16 amp EV charging
30 amp breaker/wire = 24 amp EV charging
50 amp breaker/wire = 40 amp EV charging
55 amp wire (no 55 amp breakers available) = 44 amp EV charging
60 amp breaker/wire = 48 amp EV charging

The Tesla Wall Connector doesn't have a setting for a 55 amp breaker (44 amp charging), so when using NM-B 6/3 wire, your charging circuit is limited to 40 amps.

Configuring a Tesla Wall Connector to charge at 48 amps on NM-B 6/3 wire is against the NEC (National Electrical Code) and will cause you to fail an inspection since that wire is only good for a 44 amp continuous load.
 

ATPMSD

Active Member
Mar 12, 2021
1,305
1,194
Atlanta, GA
The point that often confuses people is that in the code, if you use a wire rated at 55-amps you are allowed to install a 60 amp breaker since there are no 55 amp breakers. However, for continuous load items you must also comply with the 80% rule. So while you can use a 60 amp breaker the wall connector must be set to a 50 amp circuit to remain with the 80% rule. Since the wall connector requires a dedicated circuit you really should use a 50 amp breaker as well.
 

Rocky_H

Well-Known Member
Feb 19, 2015
7,941
10,060
Boise, ID
The point that often confuses people is that in the code, if you use a wire rated at 55-amps you are allowed to install a 60 amp breaker since there are no 55 amp breakers. However, for continuous load items you must also comply with the 80% rule. So while you can use a 60 amp breaker the wall connector must be set to a 50 amp circuit to remain with the 80% rule.
Regarding your last sentence, that math isn't even right. 50/60 is 83%. But regardless, people still shouldn't be trying to calculate the 80% value from the 60 number. That's the main thing that trips people up. It's that people see the breaker round up, but then mistakenly go this one extra mental assumption further, thinking that doing that then makes the whole circuit legitimately become a full 60A circuit because of the breaker. But it doesn't. It's still a 55A rated one because of the wire limitation. But most charging equipment just doesn't have a 55A circuit setting, so 50A is the best you can do on those.
 

ATPMSD

Active Member
Mar 12, 2021
1,305
1,194
Atlanta, GA
Regarding your last sentence, that math isn't even right. 50/60 is 83%. But regardless, people still shouldn't be trying to calculate the 80% value from the 60 number. That's the main thing that trips people up. It's that people see the breaker round up, but then mistakenly go this one extra mental assumption further, thinking that doing that then makes the whole circuit legitimately become a full 60A circuit because of the breaker. But it doesn't. It's still a 55A rated one because of the wire limitation. But most charging equipment just doesn't have a 55A circuit setting, so 50A is the best you can do on those.
Actually it is correct, as I noted there are two rules in play. If the wall connector is set to 50 amps than the wall connector maxes out at 40 amps, which is well below the 44 amp limit (80% of 55 amps). There is not harm in using a 60 amp breaker (which is allowed by code) since both rules will be complied with. My suggestion is that since the wall connector is told it is on a 50 amp circuit it is probably best to use a 50 amp breaker instead of the 60.
 
Actually it is correct, as I noted there are two rules in play. If the wall connector is set to 50 amps than the wall connector maxes out at 40 amps, which is well below the 44 amp limit (80% of 55 amps). There is not harm in using a 60 amp breaker (which is allowed by code) since both rules will be complied with. My suggestion is that since the wall connector is told it is on a 50 amp circuit it is probably best to use a 50 amp breaker instead of the 60.
I think the issue is an inspector would not pass an installation based on a software limit. If you turn around and set it to 48 the second he leaves. His signature is on the install certifying that it was safe.

Hey I get it and I'm limping by with mine set to 44amps manually on a 60 amp breaker just until I redo the wire.
 
No. That's the whole point of this thread. Look up "continuous load". In regards to the electric code, a continuous load is one that is expected to continue for 3 hours or more. When this is the case, you need to derate the circuit to 80% of the current rating for the wire and break.

15 amp breaker/wire = 12 amp EV charging
20 amp breaker/wire = 16 amp EV charging
30 amp breaker/wire = 24 amp EV charging
50 amp breaker/wire = 40 amp EV charging
55 amp wire (no 55 amp breakers available) = 44 amp EV charging
60 amp breaker/wire = 48 amp EV charging

The Tesla Wall Connector doesn't have a setting for a 55 amp breaker (44 amp charging), so when using NM-B 6/3 wire, your charging circuit is limited to 40 amps.

Configuring a Tesla Wall Connector to charge at 48 amps on NM-B 6/3 wire is against the NEC (National Electrical Code) and will cause you to fail an inspection since that wire is only good for a 44 amp continuous load.
Got it. Much appreciated. I now have 50 feet of 6/2 romex that's evidently utterly useless. Thanks again though!
 

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