tls
Well-known member
- Thread starter
- #1
Local electrician I drink with sometimes made a fairly convincing case to me yesterday that if I am putting in a second charger and thus swapping my 2-space panel used as a disconnect for a 4-space panel used as a disconnect/j-box, I am not required to follow the 125% continuous-load rule for the wiring from subpanel to main panel. That wiring now becomes a feeder serving two continuous loads which I am not required to assume will be simultaneously at full current, rather than a branch serving one continuous load.
OK so far. Wondering what @FlasherZ in particular thinks of this. But here's the galaxy-brain part.
My present setup is a single EVSE connected by about 30' of #4 XHHW in conduit. This is under a deck and though re-pulling would be possible, I don't care to do so just to get another 8A of charging ampacity by replacing with #3. Everything involved is rated for 75C so I get 85A ampacity, which I am allowed to round up the next standard breaker size, 90A. This lets me run my charger at its 90A breaker/72A load setting. The charger is a Tesla Wall Connector Gen2, which does load sharing, so I can add a second charger and they will split the 72A amongst themselves, though strict code compliance might be understood to require me to put each on its own branch circuit (the only reason it might not is that the Tesla charger manual, which is within the scope of its UL approval, says that the power wiring for two HPWCs in a load-sharing arrangement must be connected in a junction box, and in theory, if the approved device's manual says you can do it, you should be allowed to do it).
With me so far? Now hear this.
My buddy Sparky suggests that I can legally run just a couple of feet of #3 *from the new 4-space subpanel to each charger* and then place each charger on a 100A breaker, rather than a 90A breaker, even though the panel itself is fed by what is now a 90A feeder. Each (2' long...) branch circuit from subpanel to charger is compliant because the cable and OCPD are rated for 125% of the 80A continuous load. The 30' feeder back to my pain panel is also compliant because the 125% rule does not apply to feeders.
This makes a sort of perverse sense to me, and would appear to be a way to legally wire two 80A EVSEs with a single run of #4 copper from a main panel. But it has to be prohibited somewhere in the NEC, right? We have both looked for a reference forbidding a subpanel from containing a branch circuit OCPD larger than that protecting the feeder circuit for that subpanel, and we are coming up dry... taken to an extreme, this would seem to permit any number of things that really ought not be allowed so long as that small-panel-used-as-disconnect right before the EVSE has a couple of extra spaces - like an 80A EVSE and a 20A convenience outlet, together on that subpanel fed by a #4 feeder.
Speaking of "how the poco does it"...
OK so far. Wondering what @FlasherZ in particular thinks of this. But here's the galaxy-brain part.
My present setup is a single EVSE connected by about 30' of #4 XHHW in conduit. This is under a deck and though re-pulling would be possible, I don't care to do so just to get another 8A of charging ampacity by replacing with #3. Everything involved is rated for 75C so I get 85A ampacity, which I am allowed to round up the next standard breaker size, 90A. This lets me run my charger at its 90A breaker/72A load setting. The charger is a Tesla Wall Connector Gen2, which does load sharing, so I can add a second charger and they will split the 72A amongst themselves, though strict code compliance might be understood to require me to put each on its own branch circuit (the only reason it might not is that the Tesla charger manual, which is within the scope of its UL approval, says that the power wiring for two HPWCs in a load-sharing arrangement must be connected in a junction box, and in theory, if the approved device's manual says you can do it, you should be allowed to do it).
With me so far? Now hear this.
My buddy Sparky suggests that I can legally run just a couple of feet of #3 *from the new 4-space subpanel to each charger* and then place each charger on a 100A breaker, rather than a 90A breaker, even though the panel itself is fed by what is now a 90A feeder. Each (2' long...) branch circuit from subpanel to charger is compliant because the cable and OCPD are rated for 125% of the 80A continuous load. The 30' feeder back to my pain panel is also compliant because the 125% rule does not apply to feeders.
This makes a sort of perverse sense to me, and would appear to be a way to legally wire two 80A EVSEs with a single run of #4 copper from a main panel. But it has to be prohibited somewhere in the NEC, right? We have both looked for a reference forbidding a subpanel from containing a branch circuit OCPD larger than that protecting the feeder circuit for that subpanel, and we are coming up dry... taken to an extreme, this would seem to permit any number of things that really ought not be allowed so long as that small-panel-used-as-disconnect right before the EVSE has a couple of extra spaces - like an 80A EVSE and a 20A convenience outlet, together on that subpanel fed by a #4 feeder.
Speaking of "how the poco does it"...
Sponsored