Backing up 6 x 20A and 1 x 15A circuits with one Powerwall?

[Sinntax]

Hello,

Looking for some advice regarding a single Powerwall install. I have a pending order for a 4.62 kW Solar Roof with 1 Powerwall. My house has 100Amp service and I replaced my Federal Pacific Electric panel in August with an Eaton Meter Combo unit (see below, it is model MBE1224B100BTFZ). I did the stucco too and that is why it looks a bit lumpy. It was the first time I had done stucco work and I knew it would need to be ripped into later on for solar roof. I consolidated the circuits as much as possible using tandem and quad double pole BR breakers. I have six spaces (12 circuits) free in the existing panel

My water heater and dryer are both gas so they run off a 20A circuit fine. I was hoping with a single Powerwall that I could run a 100Amp sub feed breaker (Eaton model BR2100CS) off the bottom of this panel and feed it to the backup gateway and sub panel and extend the six 20A and one 15A circuit over to the backup panel. This would leave the 2 x 30A double pole quad breaker for oven and cooktop as well as the 20A furnace circuits on the existing panel and not be backed up.

Would one Powerwall be able to handle all that ok? I use about 500 KwH a month. If there is any more information needed to advise please let me know.

Thanks!

 

[lucassaugen]

It's all about draw. I've got a small house with similar specs. The whole house is backed up on a single powerwall. Works great unless we try to run the dryer (electric). It draws too many amps for a single powerwall to handle. The fix is to not run the dryer in a power outage situation. We also don't run the dryer from 4pm to 9pm because we'd end up drawing from the grid.

We run off the powerwall from 4pm to 9pm current and usually use about 25% of the powerwall each night.

 

[jboy210]

A single PowerWall 2 is rated for 5 kW continuous load. You could turn on the load you want to support and see what the meter says you are drawing.

FWIW, there are certain costs associated with the install that are fixed regardless of the number of Powerwalls (up to 9). $1000 for Tesla Gateway, $1500 for install. There is an increase from the $1500 when installing 2 Powerwalls, but it was relatively minor ($500-ish).

 

[bkp_duke]

Tesla Engineering is probably not going to let this fly.

20A x 6 + 15A = 135A peak draw, which on 120V is 16.2 kW. That's just above the max temp draw for two powerwalls. Put 80% limit on that so the breakers don't throw, and you are below the 2 PW max, but still way above the 7kw max temp draw for a single PW2.

It really comes down to what is on those breakers, if they are lights, a refrigerator, etc. that won't come close to max draw you can probably argue your way into getting what you want. But if you have a high-draw item or two on there, they may come back and tell you all circuits cannot be backed up.

 

[Ampster]

As @lucassaugen said, it is all about load, or what those circuits might draw.

 

[miimura]

If all the loads are 120V, your plan is good. The total possible draw of those circuits is nearly irrelevant because plugs and lighting almost never draw loads up to their breaker rating. However, I would back up the furnace too. It would suck to have the power out and have no heat.

 

[GenSao]

Hello,

Looking for some advice regarding a single Powerwall install. I have a pending order for a 4.62 kW Solar Roof with 1 Powerwall. My house has 100Amp service and I replaced my Federal Pacific Electric panel in August with an Eaton Meter Combo unit (see below, it is model MBE1224B100BTFZ). I did the stucco too and that is why it looks a bit lumpy. It was the first time I had done stucco work and I knew it would need to be ripped into later on for solar roof. I consolidated the circuits as much as possible using tandem and quad double pole BR breakers. I have six spaces (12 circuits) free in the existing panel

My water heater and dryer are both gas so they run off a 20A circuit fine. I was hoping with a single Powerwall that I could run a 100Amp sub feed breaker (Eaton model BR2100CS) off the bottom of this panel and feed it to the backup gateway and sub panel and extend the six 20A and one 15A circuit over to the backup panel. This would leave the 2 x 30A double pole quad breaker for oven and cooktop as well as the 20A furnace circuits on the existing panel and not be backed up.

Would one Powerwall be able to handle all that ok? I use about 500 KwH a month. If there is any more information needed to advise please let me know.

Thanks!

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View attachment 623679

Welcome to the TMC. Enjoy your stay.

Yes. All the 15A and 20A single pole (120V) circuits can easily move to the backup load panel. This includes the furnace. Typically the 30A dual pole (240V) circuits may not be added to the backup side.

Too bad you did not upsize the bus bar of your Eaton Meter Combo from 100 A to 200 A. Although your service is limited to 100 A, having a bigger bus bar (200 A) would give you installation flexibility. Although the 120% rule applies to the backup panel, I recall the main breaker box is limited to the sum of breakers (100 A). I forgot the specific NEC rule. Thus the breaker from main panel to the Tesla Gateway would be 40A (100A - 30A - 30A). Check with your installer to be sure.

 

[wwhitney]

20A x 6 + 15A = 135A peak draw, which on 120V is 16.2 kW

That's not the correct computation to do. One powerwall is probably fine. But the meter main will be emptied of all breakers, and 2 new panels will be installed, one for backed up loads, and one for non-backed up loads.

Cheers, Wayne

 

[woferry]

I don't know that two panels would be needed, non-backup loads (if there are any) could probably just stay in that service panel. My 1960 San Jose house's original 100A Zinsco was replaced with a 200A service panel ~11 years ago with a kitchen remodel, and Tesla moved more breakers / amperage than the OP has to a single PW with whole-house backup for me. My average monthly consumption was around 400 kWh pre-lockdown, it's gone up with my home office and spending more time at home, more like 650 kWh in the summer and 500-550 kWh in the fall/winter so far.

Personally I'd suggest backing up everything if they let you (which I suspect they would), assuming you're willing to be a bit more careful about what loads you run during a power outage so that you don't overload the PW inverter or deplete the battery overnight.

 

[wwhitney]

I don't know that two panels would be needed, non-backup loads (if there are any) could probably just stay in that service panel.

With a 100A bus in the service panel, and a feeder to the Backup Gateway, then one of the following rules must be satisfied to protect the 100A bus:

1) 120% rule: the main breaker in the service panel, plus 125% of the inverter output continuous currents, must not exceed 120A. If the solar inverter is 3.84 kVA (20A breaker) then with one Powerwall (30A breaker), the main breaker can be at most 70A. Or if the jurisdiction is agreeable to recognizing the Powerwall as a Power Control System (which allowance is only introduced in the 2020 NEC, not yet in force in CA), then the main breaker could stay at 100A.

2) 100% rule: the sum of the feeder to the Backup Gateway, and the double pole breakers for non-backup loads, must not exceed 100A.

Cheers, Wayne