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Auxillary Grounding Rod question for Powerwall 2 batteries

TexacoStar5

Member
Jun 3, 2021
15
6
Los Angeles
Just installed a couple of Powerwall 2 batteries that charge from the grid as we don't have solar. They discharge and power all the loads in the home during peak energy hours and are available to about half the home's circuits as backup power if we get a power outage (we got the batteries as part of the California CPUC's Equity Resilience program introduced to offset the impacts of the recent Edison and PG&E Public Safety Power Shutoff events).

We have an existing 5/8" 8' long grounding rod that the main meter/breaker panel is bonded to using #4 AWG wire. The grounding rod is buried in ground via a hole we drilled in the concrete pad directly below the main panel.

The backup load center and Tesla Gateway were installed next to the main meter/breaker panel and the batteries were installed directly below them so the linear distance from the Gateway to the bonding connector in the main panel is about 36" to 48" via the backup panel.

Since we charge from the grid and we don't have solar, is an auxillary grounding rod required? One is shown on the permit plan and is described as 'as needed' per NEC 690.47, however NEC 690.47 seems to apply to bonding photovoltaic panels and we have none.

Does anyone know if Powerwalls without solar panels need the auxillary grounding rod or is there a separate NEC reg that relates to grounding backup batteries?

Thanks in advance
 

Testicle

Member
Jan 12, 2020
9
3
England
Just installed a couple of Powerwall 2 batteries that charge from the grid as we don't have solar. They discharge and power all the loads in the home during peak energy hours and are available to about half the home's circuits as backup power if we get a power outage (we got the batteries as part of the California CPUC's Equity Resilience program introduced to offset the impacts of the recent Edison and PG&E Public Safety Power Shutoff events).

We have an existing 5/8" 8' long grounding rod that the main meter/breaker panel is bonded to using #4 AWG wire. The grounding rod is buried in ground via a hole we drilled in the concrete pad directly below the main panel.

The backup load center and Tesla Gateway were installed next to the main meter/breaker panel and the batteries were installed directly below them so the linear distance from the Gateway to the bonding connector in the main panel is about 36" to 48" via the backup panel.

Since we charge from the grid and we don't have solar, is an auxillary grounding rod required? One is shown on the permit plan and is described as 'as needed' per NEC 690.47, however NEC 690.47 seems to apply to bonding photovoltaic panels and we have none.

Does anyone know if Powerwalls without solar panels need the auxillary grounding rod or is there a separate NEC reg that relates to grounding backup batteries?

Thanks in advance
When the grid fails and your Tesla Backup Gateway isolates from the grid, you will lose the protective earth. You need an earthing rod on the isolated home side.
 
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holeydonut

Supporting Member
Jun 27, 2020
1,852
1,231
East Bay NorCal
No, the Gateway contactors only open the hot wires, not the neutral or ground.


My installers bonded neutral to ground in the Gateway 2... and put a separate ground in the main panel. So if the Gateway relay is opened or if someone opens my big azzz disconnect I guess the system is still grounded. Is your installer simply not wanting to add a second ground behind the Gateway?
 

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