-
Want to remove ads? Register an account and login to see fewer ads, and become a Supporting Member to remove almost all ads.
Powerwall 2: Installation
- Thread starter JeffreyY
- Start date
-
- Tags
- Powerwall Tesla Energy
Thanks for the link. Maybe that's where the 5" discrepancy comes from. Perhaps the top can be up to 79" but the switch is at 74"?
In case anyone needs an NEC reference for the 6' 7" rule on switches, it is 404.8(A). However, that section has an exception that seems to fit the Powerwall:
And I don't see anything in Article 705 (Interconnected Electric Power Production Sources) that would require a disconnect at the Powerwall itself that might be subject to more stringent requirements. So I'm not clear on the source of this height requirement for the switch on the Powerall.
Cheers, Wayne
And I don't see anything in Article 705 (Interconnected Electric Power Production Sources) that would require a disconnect at the Powerwall itself that might be subject to more stringent requirements. So I'm not clear on the source of this height requirement for the switch on the Powerall.
Cheers, Wayne
Isn't that meant to cover switched disconnects for high mounted thing like overhead doors motors or radiant heaters "adjacent to". The Powerwall would seem to be an integrated switch. It may be a usability induced requirement vs a code requirement, especially given the owner's manual references to power cycling it.
SoundDaTrumpet
Member
I just found out that Tesla allows only a 3 ft maximum install height from the base of the Powerwall. This requirement, in my mind, seems to be procedural (available equipment and manpower factors) and safety related (lifting equipment, usability, OSHA, etc.).
Did you ever get a chance to get a photo? I'm interested in seeing how that was installed. Thanks!
Maybe you talked to the same contractor that I just talked to. He wanted to install a 400A subpanel, and I when I questioned him about it, he said the the additional current from the two powerwalls necessitated either a larger panel than my current 200A panel, or the main panel could be derated by installing a smaller service disconnect breaker. I don't have a formal proposal from him, yet, but he said derating the main panel would only save a few hundred dollars.
Ahh. Replacing the main panel with a 400 Amp rated one with bigger bus bars lets you keep a 200 Amp main breaker. Electrician may be calling it a sub panel because once the gateway goes in after the meter, the GW becomes the service disconnecting means and the next panel is a sub panel with isolated neutral.
Root issue being the PW outputs combined with the main breaker could overload the 200a panel's bus bars, same issue with PV.
All this assumes you have all loads backed up. Otherwise meter panel GW panel PW
strider
Active Member
Now I am NOT an electrician but in doing my reading, with 200A from the grid, plus solar, plus PW you can overdrive the bus bars inside the panel so some advise upgrading the panel to have larger bus bars.
SoundDaTrumpet
Member
Similar situation here with 200A combination meter and load center. Tesla designed in a 175A "main breaker." (See optional read below) I questioned Tesla about this as I wanted to add more loads in the future (water heater circuit, 2nd EV charger). The explanation is from overloading the bus bars of the NEW backup loads sub-panel with solar and Powerwall. One of those ah-ha moments. Fortunately, their NEC load calculation is currently just under 175A.
Optional read: Just noticed the make and model of new backup load panel is 225A. This means with a 175A breaker in the main service panel (MSP) feeding the new backup load panel leaves (225*20%+(225-175)) 95A available for 80A of backfeed (PV generation 20A + battery discharge 2x30A). Technically I can't add 3rd PW with current design. This is likely a maxed out design.
Last edited:
So the situation with respect to panel sizing with multiple power sources is a bit more complicated than has been presented so far. It is covered in the California Electric Code (or the NEC) section 705.12(D). Here's my attempt to paraphrase the rules (2014 NEC/2016 CEC):
First, a feeder is any circuit wiring that is between the utility service disconnect and the final circuit breaker supplying the load. So the wiring between two panels is a feeder. In the simplest case a feeder will just have two ends. But it is possible to splice into the middle of a feeder, which allows you to create more complicated trees. The second simplest case would be one splice in the middle of a feeder to create 3 ends: one on the utility side and two others. This is one way to interconnect an alternate power source (solar or batteries), with a feeder splice.
705.12(D)(1) addresses feeder splices. The issue is that if one end is the utility, the second end is the alternate source, and the third end is the load, the segment going to the load end could be overloaded. The requirement is that either that load end segment is sized to accommodate both power sources, or that the segment ends in an overcurrent device. So if you have, say a 200A feeder from a 200A service disconnect to a 200A panel, then if that 200A panel has a main breaker, you could splice into the feeder to connect up to 200A of alternate power sources. If that 200A panel doesn't have a main breaker (it's MLO, main lug only), then you can't splice into that feeder without upgrading the feeder conductors between the splice and the MLO panel for the combined available current sources. [Plus the MLO panel's busbar would have to have a comparable rating.]
705.12(D)(3) address panels, more specifically the busbars in a panel that gets power from more than one connection to those bus bars. The busbars have to be protected by one of 3 methods:
(a) The busbar's rating meets or exceeds the sum of all current sources feeding the busbar.
(b) The busbar is fed from only two connections, which are on opposite ends of the busbar. Then the sum of the current sources feeding the busbar may be up to 125% of the rating of the busbar.
(c) Ignoring the main breaker (if any), the sum of the ratings of all the breakers in the panel is less than or equal to the rating of the busbar.
Those are the NEC rules for sizing equipment that is fed from multiple power sources. Tesla might have other policies beyond those, but I'm not aware of any. I'll followup with how this all impacts most Powerwall installations.
Cheers, Wayne
First, a feeder is any circuit wiring that is between the utility service disconnect and the final circuit breaker supplying the load. So the wiring between two panels is a feeder. In the simplest case a feeder will just have two ends. But it is possible to splice into the middle of a feeder, which allows you to create more complicated trees. The second simplest case would be one splice in the middle of a feeder to create 3 ends: one on the utility side and two others. This is one way to interconnect an alternate power source (solar or batteries), with a feeder splice.
705.12(D)(1) addresses feeder splices. The issue is that if one end is the utility, the second end is the alternate source, and the third end is the load, the segment going to the load end could be overloaded. The requirement is that either that load end segment is sized to accommodate both power sources, or that the segment ends in an overcurrent device. So if you have, say a 200A feeder from a 200A service disconnect to a 200A panel, then if that 200A panel has a main breaker, you could splice into the feeder to connect up to 200A of alternate power sources. If that 200A panel doesn't have a main breaker (it's MLO, main lug only), then you can't splice into that feeder without upgrading the feeder conductors between the splice and the MLO panel for the combined available current sources. [Plus the MLO panel's busbar would have to have a comparable rating.]
705.12(D)(3) address panels, more specifically the busbars in a panel that gets power from more than one connection to those bus bars. The busbars have to be protected by one of 3 methods:
(a) The busbar's rating meets or exceeds the sum of all current sources feeding the busbar.
(b) The busbar is fed from only two connections, which are on opposite ends of the busbar. Then the sum of the current sources feeding the busbar may be up to 125% of the rating of the busbar.
(c) Ignoring the main breaker (if any), the sum of the ratings of all the breakers in the panel is less than or equal to the rating of the busbar.
Those are the NEC rules for sizing equipment that is fed from multiple power sources. Tesla might have other policies beyond those, but I'm not aware of any. I'll followup with how this all impacts most Powerwall installations.
Cheers, Wayne
Last edited:
So the point of all the above is that the simplest case for Tesla to install one or more Powerwalls is when the service disconnect is in its own enclosure, and there is a feeder to a separate panel with a main breaker for all the loads. Then assuming that all the loads are to be backed up (and that enough Powerwalls are installed to do that, based on the largest size of the breakers for the loads in the load panel), the Backup Gateway can be inserted into that main feeder.
The Backup Gateway has one set of lugs on the line (utility) side and two sets of lugs on the load side. So the intercepted feeder from the service disconnect goes to the line side lugs, and a feeder is run from one set of the load side lugs to the existing load panel. Another feeder is run the other set of the load side lugs to a panel dedicated to the Powerwall.
This arrangement effectively makes a feeder splice, and because the loads panel has a main breaker, the feeder splice works under 705.12(D)(1). There is no need to deal with the busbar ratings of the panels under 705.12(D)(3), as the load panel is fed via only one connection. [The service disconnect, assuming it has only one breaker in it, qualifies under 705.12(D)(3).] If the load panel doesn't have a main breaker, one would have to be installed, or if that is not possible, a standalone single breaker disconnect could be installed between the Backup Gateway and the loads panel.
Now a very difficult way to configure a Powerwall installation would be to daisy chain all the panels, with the service disconnect at one end, and the Powerwall panel at the other end. Then all the panels need to be qualified under 705.12(D)(3). So this is a configuration to be avoided if possible.
Now if you are starting with an all-in-one meter, service disconnect, and load panel, the job is much harder. If the internal wiring from the meter to the integral service disconnect can be reconfigured, then it would be possible to install the Backup Gateway as in the first case above. The Backup Gateway can accept a main breaker on the line side andbecome the service disconnect. If the wiring from the meter to the main breaker can't be reconfigured, then you effectively have to do the 'daisy chained' installation, with the difficulties that implies.
Sorry if these posts have been too long. I just have this reaction that it is silly for contractors to start talking about 400A panels on a 200A service, there's almost never a need to configure things that way.
Cheers, Wayne
The Backup Gateway has one set of lugs on the line (utility) side and two sets of lugs on the load side. So the intercepted feeder from the service disconnect goes to the line side lugs, and a feeder is run from one set of the load side lugs to the existing load panel. Another feeder is run the other set of the load side lugs to a panel dedicated to the Powerwall.
This arrangement effectively makes a feeder splice, and because the loads panel has a main breaker, the feeder splice works under 705.12(D)(1). There is no need to deal with the busbar ratings of the panels under 705.12(D)(3), as the load panel is fed via only one connection. [The service disconnect, assuming it has only one breaker in it, qualifies under 705.12(D)(3).] If the load panel doesn't have a main breaker, one would have to be installed, or if that is not possible, a standalone single breaker disconnect could be installed between the Backup Gateway and the loads panel.
Now a very difficult way to configure a Powerwall installation would be to daisy chain all the panels, with the service disconnect at one end, and the Powerwall panel at the other end. Then all the panels need to be qualified under 705.12(D)(3). So this is a configuration to be avoided if possible.
Now if you are starting with an all-in-one meter, service disconnect, and load panel, the job is much harder. If the internal wiring from the meter to the integral service disconnect can be reconfigured, then it would be possible to install the Backup Gateway as in the first case above. The Backup Gateway can accept a main breaker on the line side andbecome the service disconnect. If the wiring from the meter to the main breaker can't be reconfigured, then you effectively have to do the 'daisy chained' installation, with the difficulties that implies.
Sorry if these posts have been too long. I just have this reaction that it is silly for contractors to start talking about 400A panels on a 200A service, there's almost never a need to configure things that way.
Cheers, Wayne
Last edited:
Thanks for write up. One question,
Is the difficulty you mention due to the possibility of the PWs backfeeding through the GW into the upstream panel? If the PW/GW are configured as backup only (or with a main panel appropriate backflow limit via CT on service entrance), then there would not be the potential of overloading the main panel.
If that complication is removed. It seems like a 200 amp panel derated to 100A would work well for backed up loads. If you have a dedicated backup panel, even with 4 Powerwalls, the most they will supply is 80 amps continuous. So the panel loads would then be less than 80 amps. With 80 amps from PW and a 100 Amp main (or 100 Amp feeder breaker and main lug) a 200 amp panel is still good. Alternatively, 100+120 is less than 125% of 200. PW are lower current when charging, so plenty of margin there along with GW monitoring.
Is the difficulty you mention due to the possibility of the PWs backfeeding through the GW into the upstream panel? If the PW/GW are configured as backup only (or with a main panel appropriate backflow limit via CT on service entrance), then there would not be the potential of overloading the main panel.
If that complication is removed. It seems like a 200 amp panel derated to 100A would work well for backed up loads. If you have a dedicated backup panel, even with 4 Powerwalls, the most they will supply is 80 amps continuous. So the panel loads would then be less than 80 amps. With 80 amps from PW and a 100 Amp main (or 100 Amp feeder breaker and main lug) a 200 amp panel is still good. Alternatively, 100+120 is less than 125% of 200. PW are lower current when charging, so plenty of margin there along with GW monitoring.
The difficulty is qualifying the panel busbars under 705.12(D)(3). In a daisy chain configuration, every panel has to qualify, and the currents from the utility, batteries and solar (if present) add, design-wise.
The NEC isn't going to recognize such control mechanisms, what matters is the continuous inverter output current, 125% of that is the figure used for checking feeders and panel buses.
The inverter in each Powerwall is rated at 5800 VA continuous apparent power, which at 240V works out to 24.17 amps. 125% of that is 30.2 amps, but as the Powerwalls are connected via 30 amp breakers, we can round down to 30 amps. 30 amps per Powerwall is the figured required to be used for 705.12(D)(3) computations.
Cheers, Wayne
@wwhitney - thank you for this write-up. It makes it clear why the drawings for my PowerWall install have separated the generation and loads. They are going to put the solar (2x20A 240V) and PowerWalls (2x30A 240V) in one "Generation Panel" on one load side gateway lug and the "Backup Panel" on the other load side gateway lug. I thought it would have been simpler to just put a breaker in the Generation Panel to feed the existing sub-panel which has all the backed-up loads, but the 100 amps of generation and 125A sub-panel breaker cannot go in one 200A panel.
Or could it? I would have 4 generation breakers at the bottom of the panel totaling 100 amps (solar + PowerWalls), in the middle is a 125 amp sub-panel load breaker, then the top of the panel would have the breaker that goes to the gateway. Could that be 125 amps? 225 amps of current source breakers feeding a 200A panel bus is less than 125%, but do the 4 breakers qualify as a source at one end of a feeder?
I currently have a 400A main panel with a 200A breaker from the meter and the 2x20A solar circuits at the bottom. They insisted that they be at the bottom, but for these purposes, the panel is so over-sized it doesn't matter.
Or could it? I would have 4 generation breakers at the bottom of the panel totaling 100 amps (solar + PowerWalls), in the middle is a 125 amp sub-panel load breaker, then the top of the panel would have the breaker that goes to the gateway. Could that be 125 amps? 225 amps of current source breakers feeding a 200A panel bus is less than 125%, but do the 4 breakers qualify as a source at one end of a feeder?
I currently have a 400A main panel with a 200A breaker from the meter and the 2x20A solar circuits at the bottom. They insisted that they be at the bottom, but for these purposes, the panel is so over-sized it doesn't matter.
@wwhitney going to see if I have this right, please correct.
If I understand your plan correctly, it sounds correct.
Main panel: 400A rated, 200A main, 125A to Gateway at bottom (not that it matters)
Gateway: no breaker, load lugs to generation panel
Generation panel: 125A main breaker, 125A breaker to load panel, 2x20&2x30 at bottom
Load panel: 125A main breaker and loads
NEC:
Main: (125+200)<400 OK
Generation: (125+100)<(125% × 200A) (generation, (a)), note: need PW charging and loads to match the 125A breaker. With PV at the very bottom and PW the next space above, it seems like it meets the intent of the NEC (worst case the loads are fed from both directions on the bus bar)
One question: why the 125A breaker to backed up loads vs 100A to match max generation? The issue may be a lack of plug in 125A breakers.
Why would that be simpler? If the critical loads subpanel has a main breaker in your scenario, it is just one more breaker that is duplicative. If the critical loads subpanel would be MLO in your example, it's just shuffling breakers around.
I would say yes. So a panel with a 200A bus, a 125A feed on the utility side at one end of the bus, and a 100A feed from alternate sources at the other end of the bus would qualify under 705.12(D)(3)(b)
Cheers, Wayne
Frankman60
Member
I think you may be right because a contractor (not Tesla) said that two PWs could be stacked on an outside wall which would place the switch on the top PW at about 85 inches. This is not a problem for me because if the top PW needs to be rebooted I could still reach the switch.
Well, everything is just shuffling things around. I was trying to reduce equipment cost. The existing sub-panel has no main breaker, just the breaker feeding it in the main panel. That breaker and the feed has to be moved behind the gateway so it can be backed up. The install docs propose a completely new 200A panel on the outside of the house to "relocate loads" from the main panel. IIRC, the only loads that need to be relocated are this one subpanel and one bedroom AFCI circuit which also has my Enphase Envoy on it. So I am proposing eliminating one panel in the install and using only one load lug on the gateway.
When they talk about stacked Powerwalls, don't they mean they are at the same level, like books in a bookcase with only one Powerwall attached to the wall and the others stacked in front of it?
