Upgrading to 400 Amp service after Solar already installed

[Eric33432]

My 600 amp (CL 480 meter) service is similarly split, but into 3 200 amp main breakers. The transfer switches contain the main breakers within them.

Cables from the load side of the meter go to each transfer switch through the "gutter" above the meter and transfer switches, and each transfer switch feeds a 200 amp 40 position breaker panel located in one of the garages. (The smaller panel to the immediate left of the meter is for the pool equipment). I have straight solar ordered (no Powerwalls). I would be a lot of work to feed each of these transfer switches with Tesla gateways, and I would need a bunch of Powerwalls, and there is no room available on this wall to add three Tesla gateways and two inverters.

I imagine Tesla will install an "inverter panel" on the right side of my electric meter when they install my solar, and not mess with the existing transfer switches. I am still waiting on Tesla to complete my "site survey".

The 60 KW generator can probably handle charging my Model X and future Model Y, since I charge overnight when the demand is at its lowest, but I need to figure out some way to not have that happen. No need to stress the generator charging the cars. Perhaps a way needs to be worked out to normally not have the cars charge when operating on the generator, but be able to override that in the event of a multi day outage like we had during Irma when the power was out in my neighborhood for 6 days (I am between the Intracoastal and the Atlantic Ocean, 2 blocks from the ocean!)

It would be interesting to know what the OP decided to do!

 

[Eric33432]

Download “mike holt’s electrical toolbox”, it runs the alternate loads calculation which is less conservative..

I did just that, result below.

In my experience, houses with more than 400 amp services often have services that are over designed. Note my house is set up with a 600 amp (CL480) Service, built in 2006, and even with two 48 amp EV circuits, Mike Holt's electrical toolbox says I only need a 350 amp main disconnect.

Note we use gas for hot water and the cooktop, but there is a circuit installed for an electric cooktop. I ran the calculation below with the cooktop circuit in the calculation.

When I eliminated the EVs, this calculator came up with a service disconnect rating of 300 amps, half my installed capacity of 600 amps. But I am glad to have all this extra capability. Who knows, some day we might have 3 or even 4 EVs!

A 300 amp service would have been perfectly adequate when the house was built in 2006. I would probably have installed two 200 amp disconnects feeding two 200 amp panels if the inspector would have allowed for that (with a couple of sub panels since 80 circuit panels were not allowed in 2006).

USER INPUTS:

A. General Lighting/Receptacles:

Living Area in Sq. Ft.:8500sq. ft.

Small Appliance Circuits: 4 Circuits

Laundry Circuit(s): 2 Circuit(s)

B. Fixed Appliances and Equipment:

Dishwasher(s), 120V:2Unit(s),12 Amperes

Disposal(s), 120V:1Unit(s),10 Amperes

Electric Vehicle Charger(s), 240V:2Unit(s),48 Amperes

Elevator(s), 240V:1Unit(s),20 Amperes

Microwave(s), 120V:1Unit(s),1800 VA

Pool Pump(s), 240V: 1Unit(s),2 Horsepower

Pool Heater(s), 240V:1Unit(s),27 Amperes

Electric Dryer(s), 240V:1Unit(s),5000 VA

Electric Cooktops(s), 240V:1Unit(s),7200 VA

Oven Double(s), 240V:1Unit(s),7200 VA

C. Cooling/Heating Load(s):

Cooling Load: AC/Condenser

103.3A and Fan 11.04A, 240V

Heating Load: Heat

43400 VA and Fan 18.8A, 240V

COPPER RESULTS

1. Service Disconnect Rating: 350A

2. Service Conductor Size: 350 kcmil, rated 310A at 75°C

3. Service Neutral Conductor Size: 3 AWG, rated 100A at 75°C

4. Supply-Side Bonding Jumper: 3 AWG

5. Raceway Size: 3 Inch

ALUMINUM RESULTS

1. Service Disconnect Rating: 350A

2. Service Conductor Size: 500 kcmilAL, rated 310A at 75°C

3. Service Neutral Conductor Size: 2 AWGAL, rated 90A at 75°C

4. Supply-Side Bonding Jumper: 1 AWGAL

5. Raceway Size: 3½ Inch


Service Calculation[220.82(B)]

A. General Lighting/Receptacles:

Living Area: 8500 x 3 VA = 25500VA

Small Appliance Circuits: 1,500 VA x 4 = 6000VA

Laundry Circuit(s): 1,500 VA x 2 = 3000

B. Fixed Appliances and Equipment

Dishwasher(s), 120V:2Unit(s) x 12 Amperes x 120V =2880VA

Disposal(s), 120V:1Unit(s) x 10 Amperes x 120V =1200VA

Electric Vehicle Charger(s), 240V:2Unit(s) x 48 Amperes x 240V =23040VA

Elevator(s), 240V:1Unit(s) x 20 Amperes x 240V =4800VA

Microwave(s), 120V:1Unit(s) x 1800 VA = 1800 VA

Pool Pump(s), 240V:1Unit(s) x 2 Horsepower = 2880VA

Pool Heater(s), 240V:1Unit(s) x 27 Amperes x 240V =6480VA

Dryer, 240V:1Unit(s), 5000VA

Electric Cooktops(s), 240V:1Unit(s), 7200VA

Oven Double(s), 240V:1Unit(s), 7200VA

Subtotal: 96980VA

First 10,000 VA at 100%: 10000

Remainder 86980 VA at 40% = 34792 VA

Subtotal Demand Load: 44792 VA

C. Cooling/Heating Load(s) [220.82(C)]:

Cooling Load at 100%: 240V x (103.3A + 11.04 A) = 27441.6 VA

Heating Load at 65%: [43400VA +(240V x 18.8 A)] x 65% = 12457.12 VA

Heating Load at 40%: [43400VA +(240V x 18.8 A)] x 40% = 11498.88 VA

[Omit Per 220.60]

Cooling/Heating Demand Load: 27442 VA

Total Service Demand Load:

Service Demand VA Load (A, B, and C):72234 VA

Service Load in Amperes: 301A ( 72234 VA/240V)

NOTES:

1. Service Disconnect Rating [240.4 and 240.6(A)]

Service disconnect sized must have an ampacity of at least 301A

Service Disconnect Rating: 350A

2. Service Conductor Size [310.15(B)(7) and Table 310.15(B)(16)]

Service conductor sized to 83% of 350A service disconnect rating.

350x 83% = 290.5A

3. Service Neutral Conductor Size [220.61 and Table 310.15(B)(16)]

A. General Lighting, Small Appliance, and Laundry VA Load: [220.42]

General Lighting: 8500 sq. ft. x 3 VA = 25500 VA

Small Appliance Circuits: 1,500 VA x 4 = 6000 VA

Laundry Circuit(s): 1,500 VA x 2 = 3000 VA

First 3,000 VA at 100% = 3000 VA

Remainder, 31500 VA at 35% = 11025 VA

General Lighting, Small Appliance, and Laundry Demand Load: 14025

B. Appliance(s) VA Load:

Dishwasher(s), 120V:2Unit(s) x 12 Amperes

Total: 4440 VA x 75% = 3330 VA, 220.53

Disposal(s), 120V:1Unit(s) x 10 Amperes

Total: 4440 VA x 75% = 3330 VA, 220.53

Microwave(s), 120V:1Unit(s) x 1800 VA

Total: 4440 VA x 75% = 3330 VA, 220.53

C. Dryer(s) VA Load [220.60]

Neutral Demand Load [220.61(B)]

5000VA x 70% = 3500 VA, 220.54

D. Cooking Equipment VA Load [220.61] and Table 220.55

Neutral Demand Load [220.61(B)]

0 VA x 70% = 0 VA, 220.55

Neutral VA Demand Load(A, B, C, and D)

14025 VA + 3330 VA + 3500 VA + 0 VA = 20855 VA

Neutral Load in Amperes:

87A (20855 VA/240V)

4. Supply-side Bonding Jumper Size [250.102(C)]

Supply-side bonding jumper sized to the service conductor size.

5. Raceway Size [Chapter 9, Table 1]

Based on a raceway at 40% fill, with an equipment grounding conductor.

 

[STS-134]

I did just that, result below.

In my experience, houses with more than 400 amp services often have services that are over designed. Note my house is set up with a 600 amp (CL480) Service, built in 2006, and even with two 48 amp EV circuits, Mike Holt's electrical toolbox says I only need a 350 amp main disconnect.

Note we use gas for hot water and the cooktop, but there is a circuit installed for an electric cooktop. I ran the calculation below with the cooktop circuit in the calculation.

When I eliminated the EVs, this calculator came up with a service disconnect rating of 300 amps, half my installed capacity of 600 amps. But I am glad to have all this extra capability. Who knows, some day we might have 3 or even 4 EVs!

Well you want enough capacity for 4*80A = 320A. J1772 allows up to 80A, and if every one of your 4 EVs has a 80A OBC, you'll need 320A to power them all simultaneously. Which means you have "only" 160A for everything else in the house before hitting your CL480 limit.

 

[Vines]

I did just that, result below.

In my experience, houses with more than 400 amp services often have services that are over designed. Note my house is set up with a 600 amp (CL480) Service, built in 2006, and even with two 48 amp EV circuits, Mike Holt's electrical toolbox says I only need a 350 amp main disconnect.

Note we use gas for hot water and the cooktop, but there is a circuit installed for an electric cooktop. I ran the calculation below with the cooktop circuit in the calculation.

When I eliminated the EVs, this calculator came up with a service disconnect rating of 300 amps, half my installed capacity of 600 amps. But I am glad to have all this extra capability. Who knows, some day we might have 3 or even 4 EVs!

A 300 amp service would have been perfectly adequate when the house was built in 2006. I would probably have installed two 200 amp disconnects feeding two 200 amp panels if the inspector would have allowed for that (with a couple of sub panels since 80 circuit panels were not allowed in 2006).

USER INPUTS:

A. General Lighting/Receptacles:

Living Area in Sq. Ft.:8500sq. ft.

Small Appliance Circuits: 4 Circuits

Laundry Circuit(s): 2 Circuit(s)

B. Fixed Appliances and Equipment:

Dishwasher(s), 120V:2Unit(s),12 Amperes

Disposal(s), 120V:1Unit(s),10 Amperes

Electric Vehicle Charger(s), 240V:2Unit(s),48 Amperes

Elevator(s), 240V:1Unit(s),20 Amperes

Microwave(s), 120V:1Unit(s),1800 VA

Pool Pump(s), 240V: 1Unit(s),2 Horsepower

Pool Heater(s), 240V:1Unit(s),27 Amperes

Electric Dryer(s), 240V:1Unit(s),5000 VA

Electric Cooktops(s), 240V:1Unit(s),7200 VA

Oven Double(s), 240V:1Unit(s),7200 VA

C. Cooling/Heating Load(s):

Cooling Load: AC/Condenser

103.3A and Fan 11.04A, 240V

Heating Load: Heat

43400 VA and Fan 18.8A, 240V

COPPER RESULTS

1. Service Disconnect Rating: 350A

2. Service Conductor Size: 350 kcmil, rated 310A at 75°C

3. Service Neutral Conductor Size: 3 AWG, rated 100A at 75°C

4. Supply-Side Bonding Jumper: 3 AWG

5. Raceway Size: 3 Inch

ALUMINUM RESULTS

1. Service Disconnect Rating: 350A

2. Service Conductor Size: 500 kcmilAL, rated 310A at 75°C

3. Service Neutral Conductor Size: 2 AWGAL, rated 90A at 75°C

4. Supply-Side Bonding Jumper: 1 AWGAL

5. Raceway Size: 3½ Inch


Service Calculation[220.82(B)]

A. General Lighting/Receptacles:

Living Area: 8500 x 3 VA = 25500VA

Small Appliance Circuits: 1,500 VA x 4 = 6000VA

Laundry Circuit(s): 1,500 VA x 2 = 3000

B. Fixed Appliances and Equipment

Dishwasher(s), 120V:2Unit(s) x 12 Amperes x 120V =2880VA

Disposal(s), 120V:1Unit(s) x 10 Amperes x 120V =1200VA

Electric Vehicle Charger(s), 240V:2Unit(s) x 48 Amperes x 240V =23040VA

Elevator(s), 240V:1Unit(s) x 20 Amperes x 240V =4800VA

Microwave(s), 120V:1Unit(s) x 1800 VA = 1800 VA

Pool Pump(s), 240V:1Unit(s) x 2 Horsepower = 2880VA

Pool Heater(s), 240V:1Unit(s) x 27 Amperes x 240V =6480VA

Dryer, 240V:1Unit(s), 5000VA

Electric Cooktops(s), 240V:1Unit(s), 7200VA

Oven Double(s), 240V:1Unit(s), 7200VA

Subtotal: 96980VA

First 10,000 VA at 100%: 10000

Remainder 86980 VA at 40% = 34792 VA

Subtotal Demand Load: 44792 VA

C. Cooling/Heating Load(s) [220.82(C)]:

Cooling Load at 100%: 240V x (103.3A + 11.04 A) = 27441.6 VA

Heating Load at 65%: [43400VA +(240V x 18.8 A)] x 65% = 12457.12 VA

Heating Load at 40%: [43400VA +(240V x 18.8 A)] x 40% = 11498.88 VA

[Omit Per 220.60]

Cooling/Heating Demand Load: 27442 VA

Total Service Demand Load:

Service Demand VA Load (A, B, and C):72234 VA

Service Load in Amperes: 301A ( 72234 VA/240V)

NOTES:

1. Service Disconnect Rating [240.4 and 240.6(A)]

Service disconnect sized must have an ampacity of at least 301A

Service Disconnect Rating: 350A

2. Service Conductor Size [310.15(B)(7) and Table 310.15(B)(16)]

Service conductor sized to 83% of 350A service disconnect rating.

350x 83% = 290.5A

3. Service Neutral Conductor Size [220.61 and Table 310.15(B)(16)]

A. General Lighting, Small Appliance, and Laundry VA Load: [220.42]

General Lighting: 8500 sq. ft. x 3 VA = 25500 VA

Small Appliance Circuits: 1,500 VA x 4 = 6000 VA

Laundry Circuit(s): 1,500 VA x 2 = 3000 VA

First 3,000 VA at 100% = 3000 VA

Remainder, 31500 VA at 35% = 11025 VA

General Lighting, Small Appliance, and Laundry Demand Load: 14025

B. Appliance(s) VA Load:

Dishwasher(s), 120V:2Unit(s) x 12 Amperes

Total: 4440 VA x 75% = 3330 VA, 220.53

Disposal(s), 120V:1Unit(s) x 10 Amperes

Total: 4440 VA x 75% = 3330 VA, 220.53

Microwave(s), 120V:1Unit(s) x 1800 VA

Total: 4440 VA x 75% = 3330 VA, 220.53

C. Dryer(s) VA Load [220.60]

Neutral Demand Load [220.61(B)]

5000VA x 70% = 3500 VA, 220.54

D. Cooking Equipment VA Load [220.61] and Table 220.55

Neutral Demand Load [220.61(B)]

0 VA x 70% = 0 VA, 220.55

Neutral VA Demand Load(A, B, C, and D)

14025 VA + 3330 VA + 3500 VA + 0 VA = 20855 VA

Neutral Load in Amperes:

87A (20855 VA/240V)

4. Supply-side Bonding Jumper Size [250.102(C)]

Supply-side bonding jumper sized to the service conductor size.

5. Raceway Size [Chapter 9, Table 1]

Based on a raceway at 40% fill, with an equipment grounding conductor.

You are correct that the vast majority of people do not need 600A, there are those with a wood shop hobby, or a ceramics hobby who might appreciate the extra power. Who knows, when the Cybertruck and other large EVs arrive, there might be a charger that maxes out at a 100A circuit again.

Practically though, the builder probably made a calculated choice to add some capacity here since it's such a large undertaking to add later. It was probably only less than 50k additionally to get this capacity (over 400A of capacity) when building the house and the design life of a service for a home is a long time.

 

[jshutterbug]

To start with I am NOT an electrician and have very little knowledge of electrical loads. We are in the process of a complete remodel of our home, and in order to "future proof" our house, our architect suggested upgrading our electrical panel as well. When I initiated the purchase of my solar system from Tesla in May, 2021, I also started a request to upgrade my existing service panel (main panel) to 400 amps from PG&E. Silly me thought that I would have had the new panel in way before Tesla would come to install the system. Tesla installed the solar system in September, 2021 and we got our PTO in February, 2022. PG&E finally gave us the approval for our panel upgrade in May, 2022. We have a 12.24 kW Solar system with 2 PowerWalls that is attached to our existing electrical panel. I can't get a straight answer from my GC, electrician or PG&E as to what our current service panel is? Some say it is 100 - others say it is 125 and others say it is 170. If that part wasn't frustrating enough, now we are in the process of trenching to install our new 400 amp panel and we noticed that the Tesla backup-switch on our meter says it is only rated for 200 Amps. Initially, we didn't know what this thing was, but we have come to find out that this is what provides our "whole house" to be backed up during a power outage. We recently had a power outage and this sucker worked flawlessly so we DO NOT want to be without it. PG&E doesn't seem to have any knowledgeable folks about what this thing does or how to integrate it with the new panel. I have been trying to contact Tesla for 3 months now to find out if I can use my existing "meter collar/backup switch" on a 400 amp service panel. I have called and emailed Tesla at their energy support email ([email protected]) for months and have not gotten ANY replies. I have asked if we could somehow “split” the 400 amp panel into two 200 amp panels, but PG&E will only allow us to have 1 meter – and if the Tesla backup switch/collar goes on that meter, I would no longer have the “whole house” backed up. I’m wondering if anyone else has come across this situation. We went with the 400 amp service panel because we wanted to have 2 Tesla chargers (we have 1 now). We also will have some upgraded appliances (Sub-Zero fridge; wine fridge). If anyone has a solution or suggestions on what we should do at this point or who I can contact, I’d really appreciate it. Some additional facts: We have underground service and we would have had to trench for 200 or 400.

So what'd you end up doing? Did you originally have a 100A main panel? Did you upgrade your main panel? If so, how much was trenching?
I'm in a similar situation, I have a 100A main panel (underground service) with 4kw solar panel system on the main house. We're building an ADU in the backyard and majority of electricians said I need to upgrade main panel to minimum 200A. I've been quoted $20K for underground trenching across the street to PG&E box, PG&E fees of $8K, another $10K for panel upgrade and moving panel and existing lines away from the gas line (needs to be 3ft away). That's ~$40K just for upgrading the electrical.

The detached ADU requires solar panels to be installed so I was going to install another 4kw system with 3 Powerwalls.

I wonder if there's a way to design a system where I can keep a 100A main panel and still service the main house and the ADU. Can the system be setup in such a way that the Powerwalls supplements the power needs so it doesn't trip the main breaker. For example, if the main house is using 100A of power, can the ADU use power directly from the Powerwall to power a dryer during this time so it doesn't trip the main breaker? Or is that now things work?

 

[STS-134]

I wonder if there's a way to design a system where I can keep a 100A main panel and still service the main house and the ADU. Can the system be setup in such a way that the Powerwalls supplements the power needs so it doesn't trip the main breaker. For example, if the main house is using 100A of power, can the ADU use power directly from the Powerwall to power a dryer during this time so it doesn't trip the main breaker?

Nope because the solar is not ever guaranteed to be working at any given time, and the electrical code only allows you to attach a certain amount of potential load to the panel before you need to upgrade the panel. It's likely that the load calculations are coming in such that the panel is already almost maxed out and you cannot attach another building to it without upgrading it. My advice is to upgrade it to 400A because the trenching costs are the same regardless of how big the new service line is.

 

[Vines]

So what'd you end up doing? Did you originally have a 100A main panel? Did you upgrade your main panel? If so, how much was trenching?
I'm in a similar situation, I have a 100A main panel (underground service) with 4kw solar panel system on the main house. We're building an ADU in the backyard and majority of electricians said I need to upgrade main panel to minimum 200A. I've been quoted $20K for underground trenching across the street to PG&E box, PG&E fees of $8K, another $10K for panel upgrade and moving panel and existing lines away from the gas line (needs to be 3ft away). That's ~$40K just for upgrading the electrical.

The detached ADU requires solar panels to be installed so I was going to install another 4kw system with 3 Powerwalls.

I wonder if there's a way to design a system where I can keep a 100A main panel and still service the main house and the ADU. Can the system be setup in such a way that the Powerwalls supplements the power needs so it doesn't trip the main breaker. For example, if the main house is using 100A of power, can the ADU use power directly from the Powerwall to power a dryer during this time so it doesn't trip the main breaker? Or is that now things work?

The cost of the upgrade is about what I have seen for other similar projects. You likely won't get the building department to allow the onsite ESS to add to your load calculations for the service unless you consider it a critical operation system.

Power is required to have a habitable structure and what you propose simply isn't enough power for a new ADU plus the existing house. My advice is don't kick this can down the road, pay the money and recoup the costs with your new ADU and increased property values.

 

[STS-134]

The cost of the upgrade is about what I have seen for other similar projects. You likely won't get the building department to allow the onsite ESS to add to your load calculations for the service unless you consider it a critical operation system.

Power is required to have a habitable structure and what you propose simply isn't enough power for a new ADU plus the existing house. My advice is don't kick this can down the road, pay the money and recoup the costs with your new ADU and increased property values.

Electricians will already be on site to wire the new ADU so there wouldn't be any additional service call charges if the upgrades are done as part of one big project.

 

[BGbreeder]

Electricians will already be on site to wire the new ADU so there wouldn't be any additional service call charges if the upgrades are done as part of one big project.

Not to rain on your parade, but I do think that you are underestimating the challenge of finding an electrician, much less a company willing to take on the liability for working on a Tesla (or other 3rd party installer). There are a number of folks here who have tried and failed to find someone.

I would follow @Vines advice if I were you.

All the best,

BG

 

[jshutterbug]

The cost of the upgrade is about what I have seen for other similar projects. You likely won't get the building department to allow the onsite ESS to add to your load calculations for the service unless you consider it a critical operation system.

Power is required to have a habitable structure and what you propose simply isn't enough power for a new ADU plus the existing house. My advice is don't kick this can down the road, pay the money and recoup the costs with your new ADU and increased property values.

As usual, thanks for your input.

General question...
I was chatting with my new neighbor next door (his electricity runs off the same PG&E box across the street). He was also interested in upgrading his main panel as well so there's a possibility of us splitting the trenching cost across the street. This would benefit us both.
For a 320A line, PG&E design plans showed a 3" conduit installed in the trench from the current PG&E box to a new PG&E box on our side of the street. Would my neighbor use the same 320A line and conduit or do they have to run a separate powerline and conduit for his upgrade?

 

[Vines]

As usual, thanks for your input.

General question...
I was chatting with my new neighbor next door (his electricity runs off the same PG&E box across the street). He was also interested in upgrading his main panel as well so there's a possibility of us splitting the trenching cost across the street. This would benefit us both.
For a 320A line, PG&E design plans showed a 3" conduit installed in the trench from the current PG&E box to a new PG&E box on our side of the street. Would my neighbor use the same 320A line and conduit or do they have to run a separate powerline and conduit for his upgrade?

Happy to help when I can.

Maybe your neighbor could share your trench but that would be up to PGE. I could see them saying that joint trenching is not allowed due to some green book rule.

Certainly, you would have your own dedicated conduit (if used) and conductors. I haven't really dealt with this case so I'm not totally sure but I imagine some of the costs could be shared.

 

[STS-134]

Happy to help when I can.

Maybe your neighbor could share your trench but that would be up to PGE. I could see them saying that joint trenching is not allowed due to some green book rule.

Certainly, you would have your own dedicated conduit (if used) and conductors. I haven't really dealt with this case so I'm not totally sure but I imagine some of the costs could be shared.

When I had the trenching company out for my service upgrade, I asked about putting the new panel in the same spot as the old or going about 6 feet further down the wall of the house to the other side of the gas meter (panel must be 3 feet from the gas riser so the choice was to put it on one side or the other). There were zero additional costs for making the trench 6 feet longer because most of the costs were getting the trenching company out there to begin with. I'd imagine that in this case, if they have to dig two separate trenches, there would be additional costs, but it would probably much less than 200% of the cost to dig just one trench.

 

[Magnus0322]

Download “mike holt’s electrical toolbox”, it runs the alternate loads calculation which is less conservative..

Thanks for this. I just did mine and it came out to 146A and I have 150A service. I did the Tesla Wall Connector at 48A too. So if I ask my electrician to use the Dwelling Load Optional I should be able to install and get it permitted?

 

[Vines]

Thanks for this. I just did mine and it came out to 146A and I have 150A service. I did the Tesla Wall Connector at 48A too. So if I ask my electrician to use the Dwelling Load Optional I should be able to install and get it permitted?

Assuming the optional method is allowed in your jurisdiction then yes you should be able to get a permit based on that.