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Gen3 Wall Connector Question - load sharing?

blecchus_rex

Member
May 23, 2018
93
69
Texas, USA
Then they will each have their full 60 amps per connector if there’s just one vehicle charging, but will collectively not exceed the total when multiple are plugged in.
Yes, understood - but that also works on a single circuit as well. I'm not sure I see a functional advantage (other than allowing one connector to continue functioning in some edge case scenario where the other shorts or something) to balancing over multiple branch circuits vs balancing "within" one.

There's actual disadvantage in a scenario where you've two connectors w/ say only 60A total available on a given panel/sub-panel. If you put both on a single circuit and allow the Tesla power sharing SW to manage aggregate consumption up to the max (and allow each individually to burst up to that max when there's no contention) then you've made the most of the situation. The way the manual reads (and potentially what the code stipulates) means you'd be required to provision two separate branch circuits at 30A each. In that scenario at no point could any one connector exceed the 30A though!
 
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Darblish

Member
May 19, 2021
117
254
Columbus, OH
Yes, understood - but that also works on a single circuit as well. I'm not sure I see a functional advantage (other than allowing one connector to continue functioning in some edge case scenario where the other shorts or something) to balancing over multiple branch circuits vs balancing "within" one.

There's actual disadvantage in a scenario where you've two connectors w/ say only 60A total available on a given panel/sub-panel. If you put both on a single circuit and allow the Tesla power sharing SW to manage aggregate consumption up to the max (and allow each individually to burst up to that max when there's no contention) then you've made the most of the situation. The way the manual reads (and potentially what the code stipulates) means you'd be required to provision two separate branch circuits at 30A each. In that scenario at no point could any one connector exceed the 30A though!
I honestly can’t remember where I read it (I’m sure on this forum somewhere), but I think there was some provision for putting in significantly larger circuits as long as the devices wired to them supported some sort of compliant load-balancing scheme. I’d bet a dollar that the manual was written either when that wasn’t a thing, or in a way that minimizes Tesla’s liability if it was allowed at the time.

Separate circuits probably limits liability, too, since it means dedicated 6awg runs from the panel to the wall connector. Overcurrent tripping the main breaker is likely preferable to overcurrent heating a wire to the point of danger.
 
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Rocky_H

Well-Known Member
Feb 19, 2015
6,401
7,550
Boise, ID
There seems to still be a lot of misunderstanding flying around on this.
And from some of the electrical code I dug up a while back (but to be clear I'm definitely not an Electrician):

210.17 Electric Vehicle Branch Circuit.


But it begs the question: what's the point of the power sharing feature then?
What you just quoted is saying for an "outlet". This is not an outlet. A wall connector is a hard-wired appliance--not an outlet. So that code section does not apply.
I also understand NEC allows a managed system load to be considered the maximum permitted by that system instead of the sum of all the branch capacities (the power sharing feature in the Tesla HPWC's ostensibly providing the managed system capability). So perhaps the only real utility of the power sharing feature is to allow over-subscription at the panel / sub-panel level... and not on individual circuits?
Yes, that is what the load sharing feature is for.

The way the manual reads (and potentially what the code stipulates) means you'd be required to provision two separate branch circuits at 30A each. In that scenario at no point could any one connector exceed the 30A though!
People seem to keep mixing this up, where they think the specification of breakers means they have to be fully completely separate circuits, but that's not true. The breakers part is about a connection method. But as the manual specifies the install, you can run one single 60A line with only 60A capable wire to a subpanel. And then from there, you can hook up four wall connectors, each with their own 60A breakers and 60A wire, and their communication (if set up properly) will stay within the 60A limit of the parent connection line. The four individual ones don't all have to be separated out to smaller sized circuits. This is what the connection sharing communication is for.
 

blecchus_rex

Member
May 23, 2018
93
69
Texas, USA

Rocky_H

Well-Known Member
Feb 19, 2015
6,401
7,550
Boise, ID
Page 24: See both diagrams in which each connector is depicted on separate branch circuits.

I'm fully aware that (functionally) it works sharing multiple connectors on one circuit. That was the point of my post.
You had it right, where I agreed with you, about the circuit sharing, but then you had it wrong, staying that the 60A would then have to be split into two 30A circuits if they were sharing. I thought you could have just stopped and been right with your earlier explanation.

The point is that yes, they do fall into the definition of "branch circuits" because of the breakers, but not really "independent". You normally would not be able to overload 16 "independent" branch circuits that large onto one line with that small of a capacity. These are not really independent when they are communicating to regulate their current draw like this.
 
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TechnoBabble

Member
Mar 11, 2019
57
5
GTA
Im still not getting this. If two wall connectors are fed from a sub panel with 2 separate 60 amp breakers, how can it be acceptable that the breaker feeding the sub panel is 60 amps and be code compliant? Maybe in the states you have different codes.
If load sharing is enable this will work fine but if load sharing is disabled, wont both units cumulatively draw 96 amps causing the 60 amp sub panel breaker to overload?
This will never pass inspection around here.
 

quantumslip

Member
Mar 3, 2015
483
517
Earth
Im still not getting this. If two wall connectors are fed from a sub panel with 2 separate 60 amp breakers, how can it be acceptable that the breaker feeding the sub panel is 60 amps and be code compliant? Maybe in the states you have different codes.
If load sharing is enable this will work fine but if load sharing is disabled, wont both units cumulatively draw 96 amps causing the 60 amp sub panel breaker to overload?
This will never pass inspection around here.
I honestly can’t remember where I read it (I’m sure on this forum somewhere), but I think there was some provision for putting in significantly larger circuits as long as the devices wired to them supported some sort of compliant load-balancing scheme. I’d bet a dollar that the manual was written either when that wasn’t a thing, or in a way that minimizes Tesla’s liability if it was allowed at the time.

Separate circuits probably limits liability, too, since it means dedicated 6awg runs from the panel to the wall connector. Overcurrent tripping the main breaker is likely preferable to overcurrent heating a wire to the point of danger.

Of course that wouldn't pass if load sharing was not enabled. But you need to look at NEC 625.42 (2020 Edition):

625.42 Rating The power transfer equipment shall have sufficient rating to supply the load served. <snip> Service and feeder shall be sized in accordance with the product ratings. Where an automatic load management system is used, the maximum equipment load on a service and feeder shall be the maximum load permitted by the automatic load management system.
and then later on in the same section:
Sizing the service and feeder to match the adjusting means shall be permitted.

Tesla HPWC is an automatic load system if appropriately configured. Based on what I read the above, it is permitted by code to have the feeder or subpanel to be less than the sum of what could be the max output of the multiple HPWC, as long as the system was configured to respect the limit (ex. subpanel of 60A (so 48A continuous), each HPWC could have its own 60A breaker (48A continous) branch, but the communication between the HPWCs would be so that it would never exceed the rating of the feeder).
 
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