Installing Solar, HPWC, future proof Powerwall?

[TessiFan]

Hello everyone

I am looking to add 2 PWs and a 2nd Solar to my house and am in need of some advise. Currently, i have a 200A panel with a 200A breaker which kas a 7.36Kw solar system on a 40A breaker. I would like to add 2 PWs (60A) and a 2nd 7.2Kw Solar system (40) My plan was to:
1. add a houseload panel 200A) and mover all the loads except the pool equipment.
2. Add a 200A load center
3. Add my 2 powerwalls (60A)
4. Add my existing solar (40A) and my new solar (40A)

My question is, will this be a good solution and what size breaker would the load center need.

 

[GenSao]

Hello everyone

I am looking to add 2 PWs and a 2nd Solar to my house and am in need of some advise. Currently, i have a 200A panel with a 200A breaker which kas a 7.36Kw solar system on a 40A breaker. I would like to add 2 PWs (60A) and a 2nd 7.2Kw Solar system (40) My plan was to:
1. add a houseload panel 200A) and mover all the loads except the pool equipment.
2. Add a 200A load center
3. Add my 2 powerwalls (60A)
4. Add my existing solar (40A) and my new solar (40A)

My question is, will this be a good solution and what size breaker would the load center need. View attachment 464809

I believe you'll have to make some modifications dependent on how the existing panels are physically located.

• Assuming the Pool and EV Charger are not backed up, they will need to be placed in a "non-backup" load panel before the gateway. Likely your original load panel will be used.
• The solar and batteries can be placed into a generation panel
• All your backup loads will be moved to a new panel.
• Both the generation panel and the backup load panel will be directly connected to the gateway*.
• You'll likely have a 150 A breaker to the Tesla Gateway.
• This setup will give you better flex-ability for expansion (more powerwalls or solar).

See below layout.

* Notice the two lugs below that can be used for the Generation Panel and the Backup Load Panel. The top lugs are going to the original non-backup load panel. Photo is of my Powerwall Gateway. In my case, the powerwalls and solar could be in the same panel, but will limit future expansion.

 

[TessiFan]

wow some great information.. Thank you

 

[wwhitney]

See below layout.

One issue with your proposed layout: the "Not Backup" MLO panel doesn't meet the 120% rule, as you show 250A of breakers in it, but 120% of 200A is 240A. So it would need to be a 225A MLO panel, or one of the EV Charger or Pool breakers would have to be downsized to 40A.

Also, the "Backup" panel needs to have a main breaker in it. This is to protect the wiring between the Gateway and the "Backup" panel, as that wiring can be fed from two sources, the grid and the generation panel.

A similar strategy could be used on the grid side of the Gateway--a 200A feeder between the Service Disconnect and the Gateway can be intercepted to feed a main breaker "Not Backup" panel. This would allow the full 200A feed to the "Backup" panel without the intervening 150A breaker shown.

Cheers, Wayne

 

[GenSao]

One issue with your proposed layout: the "Not Backup" MLO panel doesn't meet the 120% rule, as you show 250A of breakers in it, but 120% of 200A is 240A. So it would need to be a 225A MLO panel, or one of the EV Charger or Pool breakers would have to be downsized to 40A.

Also, the "Backup" panel needs to have a main breaker in it. This is to protect the wiring between the Gateway and the "Backup" panel, as that wiring can be fed from two sources, the grid and the generation panel.

A similar strategy could be used on the grid side of the Gateway--a 200A feeder between the Service Disconnect and the Gateway can be intercepted to feed a main breaker "Not Backup" panel. This would allow the full 200A feed to the "Backup" panel without the intervening 150A breaker shown.

Cheers, Wayne

Wayne,

The "non-backup" panel can be tricky for me.

I did not think the 120% rule applied to the Pool or EV charger loads. Only for breakers/conductors that supply power. A website implied that NEC 690.64(B)(2), or 705.12(D)(2) states: “The sum of the ampere ratings of overcorrecting devices in circuits supplying power to a busbar or conductor shall not exceed the rating of the busbar or conductor”.

Reference: What is the Panelboard Sizing 120% Rule?

If applicable, the sub-panel discussion of another website states, "The inverter breaker in the sub-panel is the breaker to use in the calculations." Would the following apply?

200A * 120% = 240A max ampacity
30A + 30A + 40A + 40A = 140A solar and battery loads
240A - 140A = 100A available for loads in main panel?

Reference: https://www.altestore.com/blog/2018/11/grid-tied-solar-breaker-box-120-percent-rule/

I am a civil engineer, not an electrician. =)

 

[wwhitney]

The "non-backup" panel can be tricky for me.

The first paragraph of my previous post is erroneous, please disregard. Instead:

For the "Non-Backup" panel in your drawing, there are basically two options available under 705.12(D):

1) The 120% rule. You add up all the breakers capable of supplying power to the busbar (or 125% of the connected inverter rating, if that is less than the breaker rating). In your drawing that would be 200A + 40A + 40A + 30A + 30A = 340A (assuming 7.68kW solar inverters). So the busbar would need to be 340/1.2 = 283.3A minimum rating for this rule to work.

2) The "sum of all breakers rule". This excludes the breaker protecting the bus for the primary grid supply, and the total has to be less than or equal to the busbar rating. In your drawing that would be 150A + 50A + 50A, so you'd need a 250A bus.

I would say the intercepted feeder option I suggested in the third paragraph of my previous post would be the most economical way to go.

Cheers, Wayne

P.S. Your drawing shows the limitations of the simple rules in 705.12(D), as in reality that Non-Backup Panel's bus couldn't be overloaded under normal working conditions, but there is no rule in 705.12(D) to allow that arrangement. I actually proposed an amendment for the 2020 NEC to the "sum of all breakers rule" that would have covered the depicted arrangement, but it was a bit late in the process and the code making panel didn't actually take the time to understand and consider my proposed amendment.

 

[GenSao]

The first paragraph of my previous post is erroneous, please disregard. Instead:

For the "Non-Backup" panel in your drawing, there are basically two options available under 705.12(D):

1) The 120% rule. You add up all the breakers capable of supplying power to the busbar (or 125% of the connected inverter rating, if that is less than the breaker rating). In your drawing that would be 200A + 40A + 40A + 30A + 30A = 340A (assuming 7.68kW solar inverters). So the busbar would need to be 340/1.2 = 283.3A minimum rating for this rule to work.

2) The "sum of all breakers rule". This excludes the breaker protecting the bus for the primary grid supply, and the total has to be less than or equal to the busbar rating. In your drawing that would be 150A + 50A + 50A, so you'd need a 250A bus.

I would say the intercepted feeder option I suggested in the third paragraph of my previous post would be the most economical way to go.

Cheers, Wayne

P.S. Your drawing shows the limitations of the simple rules in 705.12(D), as in reality that Non-Backup Panel's bus couldn't be overloaded under normal working conditions, but there is no rule in 705.12(D) to allow that arrangement. I actually proposed an amendment for the 2020 NEC to the "sum of all breakers rule" that would have covered the depicted arrangement, but it was a bit late in the process and the code making panel didn't actually take the time to understand and consider my proposed amendment.

Wayne,

Thank you for the clarification. I agree, the Non-backup panel should not be overloaded under normal working conditions.

Hopefully your proposal (or something similar) can make it into the code next time.

 

[TessiFan]

Really great information here. So my takeaway here is to make my load center 225A as well as my MSP

 

[GenSao]

Really great information here. So my takeaway here is to make my load center 225A as well as my MSP

Depending potential physical constraints and cost, you may be forced to maintain the existing 200A busbar in "non-backup" panel (assuming reuse of an existing panel) . An option wound be to de-rate the proposed 150A breaker between the "non-backup" panel and the Tesla Gateway to 100 A. Following the "sum of all breakers rule" , 100A + 50A + 50 A = 200A.

Alternatively, if the EV charger and Pool could be located in the same sub-panel, you could have a 70A breaker to that sub panel and have a 125A breaker between the "non-backup" panel and the Tesla Gateway. Following the "sum of all breakers rule" , 125A + 70A = 195A < 200A. You'll have to manage loads.

 

[wwhitney]

The most efficient arrangement is to put a main breaker in the Not Backup Panel (as is also required in the Backup Panel). Then run the 200A feeder from the meter main runs to a splice point; from the splice point separate feeders go to the Gateway and to the Not Backup Panel. The splice point could in fact be inside the Gateway enclosure; if the Gateway had double lugs on its line side it would be easy, but the splice could be done with 3 port Polaris connectors instead.

FWIW, this is the arrangement I have, although everything is 100A instead of 200A.

Cheers, Wayne