#3 is fine:
"Local regulations" would be the municipal, county, or state's adoption of the NEC.
I have confirmed with Tesla that they do not intend to demand #2 conductors.
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#3 is fine:
"Local regulations" would be the municipal, county, or state's adoption of the NEC.
I have confirmed with Tesla that they do not intend to demand #2 conductors.
CmdrThor
Active Member
Manual says 2AWG or follow local regulations. My local regulations say 3AWG is sufficient.
Not to mention my Model X can only do 72A so I'm not worried about 80A operation. I can always set the master to a 90A breaker setting if I get a second Wall Connector and second Tesla and keep the total max charging at 72A.[/QUOTE]
Yes I keep forgetting about the "or" in that statement. But clearly someone put #2 in the manual for a reason. It doesn't seem proper to go under the recommendation in the manual because it meets local code, which is really wording for meeting the minimum passing grade.
The reason that #2 was put there is that it's the most commonly available wire gauge to support the needs of 80A charging, and it discourages residential electricians unfamiliar with the Code from using #4 to connect the HPWC. The reasoning for this is that there is a provision which allows #4 conductors to provide 100A service to an entire home, but it does not extend to subpanel feeders or branch circuits. Those electricians who know the tables will use #3.
I have confirmed that Tesla's charging team believes there is nothing wrong with using #3 to feed an HPWC and they don't consider it a "minimum passing grade" - it fully complies with Code and best practices, if available.
ccutrer
Active Member
Building codes are actually incredibly conservative, and continue to get more so with time. They have to take into account wide variability in actual manufacturing and installation of materials, so they're only "barely passing" for that part of the variables that everything has issues. On average, there's still a wide margin of error.
Well of course, that's the engineering that's gone into it. Still, it's fundamentally saying "you shall legally build no worse than this"
ssq
Member
My installation was done today. I had originally planned to get only one NEMA14-30 for a variety of reasons I have discussed and rationalized over at another thread. But as it turns out, my existing main service panel had no space left and the maker went out of business which made getting compatible breakers impossible. Long story short I ended up redesigning the entire project and doing the following (in case this is helpful for anyone else)
- Added a new 100 Amp subpanel
- Drew out two new Romex #4 on two new 100Amp breakers from the main panel to the new subpanel. Had to move some appliance breaker circuits from main panel to new subpanel to make space for the 100Amp breakers
- Put the Tesla HPWC on one dedicated 100Amp line from the main panel
- Put a NEMA14-50 on a 50 Amp breaker
Observations:
Romex #4 are a huge PITA to work with, you get a solid burn wrestling with those in tight spaces, its very hard to maneuver it inside the new HPWC L1/L2 points with rear entry. Specially with so many extremely fragile electronic circuit wires in the vicinity. Tesla should absolutely put those in a ribbon cable or some sort of protective sheath.
The Dip switches are at 1:ON, 2:ON by default. This is not the correct config for household 240V circuits - 1:OFF, 2:ON is the correct config. This is poorly illustrated in the tesla manual. It is called out in a table but there is scope for improvement - I am a design guy and I can vouch that a picture is the BEST illustration instead of lines, tables, matrices. Of course I did not read the manual since I like to guess everything by observation and race ahead (yeah, i violated RTFM
). So when I powered on the HPWC went to 3 red flashes, which means wrong dip switch setting. So yeah, a quick 30 sec call to Tesla and everything was in order.
Main Panel with two new Romex #4 capable rated at 100Amp.
New subpanel and HPWC on the side (HPWC not on this subpanel, but on a dedicated 100 Amp from the main service panel)
Final pictures, drywall refinishing and painting next. And yes I got gecko's toes from Amazon mentioned upthread. I wont like the HPWC wire banging up on the drywall and gathering paint dust.
Now what is this white wire circled in the pic below, it was frayed right out of the box and I could not find any termination point where it could have gone. Is it an extra placeholder just in case the one of the other fragile wires get damaged ? So as to not discard the entire cable and reuse it perhaps ?
- Added a new 100 Amp subpanel
- Drew out two new Romex #4 on two new 100Amp breakers from the main panel to the new subpanel. Had to move some appliance breaker circuits from main panel to new subpanel to make space for the 100Amp breakers
- Put the Tesla HPWC on one dedicated 100Amp line from the main panel
- Put a NEMA14-50 on a 50 Amp breaker
Observations:
Romex #4 are a huge PITA to work with, you get a solid burn wrestling with those in tight spaces, its very hard to maneuver it inside the new HPWC L1/L2 points with rear entry. Specially with so many extremely fragile electronic circuit wires in the vicinity. Tesla should absolutely put those in a ribbon cable or some sort of protective sheath.
The Dip switches are at 1:ON, 2:ON by default. This is not the correct config for household 240V circuits - 1:OFF, 2:ON is the correct config. This is poorly illustrated in the tesla manual. It is called out in a table but there is scope for improvement - I am a design guy and I can vouch that a picture is the BEST illustration instead of lines, tables, matrices. Of course I did not read the manual since I like to guess everything by observation and race ahead (yeah, i violated RTFM
). So when I powered on the HPWC went to 3 red flashes, which means wrong dip switch setting. So yeah, a quick 30 sec call to Tesla and everything was in order.Main Panel with two new Romex #4 capable rated at 100Amp.
New subpanel and HPWC on the side (HPWC not on this subpanel, but on a dedicated 100 Amp from the main service panel)
Final pictures, drywall refinishing and painting next. And yes I got gecko's toes from Amazon mentioned upthread. I wont like the HPWC wire banging up on the drywall and gathering paint dust.
Now what is this white wire circled in the pic below, it was frayed right out of the box and I could not find any termination point where it could have gone. Is it an extra placeholder just in case the one of the other fragile wires get damaged ? So as to not discard the entire cable and reuse it perhaps ?
#4 copper NM cable (Romex) is only good to 70A (56A Tesla charging current) because you're required to use the 60 degree column in 310.15. It's an illegal install to use it to feed an HPWC set to 80A charging. It's ok to feed your subpanel with that provided it's protected by a maximum breaker size of 70A in the main panel.
#4 is permitted to handle 100A only when it feeds an entire dwelling unit. Under all other circumstances it's good to 70A (NM/Romex, or SER when put through thermal insulation) or 85A (wire in conduit @ 75 deg termination temp). Remember that circuit ratings need to be 125% of the charging current because charging is a continuous load.
I'm not sure about that other signaling conductor, it's likely just part of the cable assembly Tesla uses and is left unused.
#4 is permitted to handle 100A only when it feeds an entire dwelling unit. Under all other circumstances it's good to 70A (NM/Romex, or SER when put through thermal insulation) or 85A (wire in conduit @ 75 deg termination temp). Remember that circuit ratings need to be 125% of the charging current because charging is a continuous load.
I'm not sure about that other signaling conductor, it's likely just part of the cable assembly Tesla uses and is left unused.
ssq
Member
Thanks for the review! I am also going to get a permit inspection done by next week. This is good to know, so perhaps I should set the HPWC to do 70Amp or less to be on the safe side. Please note my X wont be pulling any more than 48A, so does that alleviate concerns ? I reason I got the HPWC is because it gives me a better, hardwired, relatively more resilient option than UMC+NEMA14-50. Plus the added benefit of pairing it up with another HPWC on the same circuit for the Model 3 next year. I dont plan to have dual chargers on that either, happy with 48A,
ccutrer
Active Member
Heck even 4AWG THHN at 90° is only good to 95A. The electricians probably just figured "hey, we feed 100A subpanels with this all the time, so we're good, right?" It's frustrating how many electricians are unaware of different rules for different uses. For example, I have a coworker who is building a house, and has a reservation for a Model 3 (and has eyes on an X if finances would allow). I'm trying to explain to him how best to pre-wire for two charging circuits. Given that with two 14-50s totaling 100A you may as well use the new wall connector and deliver 100A to each and let them share. So he asks his [cookie cutter] builder salesman, who comes back with "k, two 220v lines to the garage, with a 14-50, 40A wiring, on a 30A breaker. Got it!" The only way I can fathom the guy ended up there is prior experiences with RVs that connect to a 14-50, but never draw nearly that much current, and certainly not continuously.
ccutrer
Active Member
You should set your wall connector to 70A/56A continuous, and replace the breaker to the wall connector and to the subpanel with 70A instead of 100A breakers. NEC rules are typically to prevent problems not just with what you currently have connected, but what anyone coming to the location might connect. I.e. if you have a friend come to visit with an 80A dual charger S, and he happens to plug in, it will still be safe.
ssq
Member
Thanks, I understand and agree, it occurred to me while my car(s) may not be a problem, a visiting car may pull more the rated/supported amperage leading to issues. I have also heard that breakers dont trip at the rated amperage but after a tad more tolerance (viz. a 50 Amp breaker would trip at 60Amp) - this sounded nonsensical to me.. curious if that's the case?
I run into this frequently, usually from electricians who provision 100A service with #4 - which is legal when serving an entire dwelling unit with 100A service. Under any other circumstances, #4 can't be used for 100A calculated load.
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