Upgrade to 400amp Service / Powerwalls, Solar, Non-backed Up Loads, Dedicated EV Meter, Oh My!

[supratachophobia]

Current setup has been up and running for about 2 years and is follows:

Utility meter brings 200amp service into non-backed up load panel with 200amp main breaker and 225 amp rated bus bar. This panel has the car charger and my second solar inverter in it. Lugs come out of the bottom and go to my battery gateway and behind that is my primary inverter, 2 Powerwalls, and my main house panel.

The breaker for the car charger goes into a separate meter provided by the utility, before it goes to the charger and the billing a much like a water deduct meter would.

Long story short, I can't add a second car charger because it would exceed the busbar rating of the non-backed loads panel so we are going to upgrade to 400 amp service and split that into 2x 200amp services using double lugs, with one dedicated to the car chargers and the other to the existing setup sans extra meter and chargers.



Now my question. Currently all the monitoring works fine, both the Tesla and the SolarEdge consumption monitor. In order to preserve said monitoring, where do I need to move the CTs to? Can I just move them into the 400amp meter box and clamp them around both wires coming from off the double lugs immediately after the main meter?

 

[ArizonaJon]

I can't answer your question but ... Do you really need to have two high current EVSEs running at the same time. If not, you can get a two headed, power sharing EVSE and save a lot of money and work.
I posted a link to the tesla solution below. There are similar units from other manufacturers for J1772.

Wall Connector Power Sharing | Tesla Support

With Power Sharing, you can allow up to six 3 Wall Connectors to share power and charge multiple vehicles at once. Learn how to set up and troubleshoot Power Sharing.

www.tesla.com

 

[supratachophobia]

I can't answer your question but ... Do you really need to have two high current EVSEs running at the same time. If not, you can get a two headed, power sharing EVSE and save a lot of money and work.
I posted a link to the tesla solution below. There are similar units from other manufacturers for J1772.

Wall Connector Power Sharing | Tesla Support

With Power Sharing, you can allow up to six 3 Wall Connectors to share power and charge multiple vehicles at once. Learn how to set up and troubleshoot Power Sharing.

www.tesla.com

Great question. Yes I could get a splitter or connect my two HPWC gen2 together over rs485. But I want to make this not only up to code but also no compromises. I'm too old to play musical cars or make sure every night that charging schedules are set right.


And we may add a second heat pump water heater down the road so I don't want to have to further pick and choose what runs when. My utility has a flat rate to upgrade service, provides the meter box at cost, and I can do most of the work alongside my licensed electrician.


As with most of my projects,I pull a Homer Simpson and I do it because I could, not necessarily because I should.

 

[mongo]

Current setup has been up and running for about 2 years and is follows:

Utility meter brings 200amp service into non-backed up load panel with 200amp main breaker and 225 amp rated bus bar. This panel has the car charger and my second solar inverter in it. Lugs come out of the bottom and go to my battery gateway and behind that is my primary inverter, 2 Powerwalls, and my main house panel.

The breaker for the car charger goes into a separate meter provided by the utility, before it goes to the charger and the billing a much like a water deduct meter would.

Long story short, I can't add a second car charger because it would exceed the busbar rating of the non-backed loads panel so we are going to upgrade to 400 amp service and split that into 2x 200amp services using double lugs, with one dedicated to the car chargers and the other to the existing setup sans extra meter and chargers.



Now my question. Currently all the monitoring works fine, both the Tesla and the SolarEdge consumption monitor. In order to preserve said monitoring, where do I need to move the CTs to? Can I just move them into the 400amp meter box and clamp them around both wires coming from off the double lugs immediately after the main meter?

Where is second PV inverter going?
Yeah you move the CTs to either pre-meter, around both cables on the feeds, or two CTs per phase. Need to check their measurement range and inner diameter.

Gen 3 WC will power share without extra wiring, but I grok the desire for more capacity.

 

[h2ofun]

Great question. Yes I could get a splitter or connect my two HPWC gen2 together over rs485. But I want to make this not only up to code but also no compromises. I'm too old to play musical cars or make sure every night that charging schedules are set right.


And we may add a second heat pump water heater down the road so I don't want to have to further pick and choose what runs when. My utility has a flat rate to upgrade service, provides the meter box at cost, and I can do most of the work alongside my licensed electrician.


As with most of my projects,I pull a Homer Simpson and I do it because I could, not necessarily because I should.

I have wired 5 wall connectors to a 200 amp feed. I could not run them all at one time, but thats not the point. I wanted the
flexibility if ever needed. I could only wire once.

 

[supratachophobia]

I have wired 5 wall connectors to a 200 amp feed. I could not run them all at one time, but thats not the point. I wanted the
flexibility if ever needed. I could only wire once.

I have no such limits.

 

[supratachophobia]

Where is second PV inverter going?
Yeah you move the CTs to either pre-meter, around both cables on the feeds, or two CTs per phase. Need to check their measurement range and inner diameter.

Gen 3 WC will power share without extra wiring, but I grok the desire for more capacity.

Second PV inverter is staying where it is, in the non backed up loads panel. I was reading that you can wrap a CT around two wires as long as they are the same phase.

If I move it to right up against the main meter, do I need to get 400amp CTs? What is the downside of having 200amp CTs and the current hitting 220,230,250 amps potentially a couple times per year? Do they become inaccurate or explode?

 

[BGbreeder]

Second PV inverter is staying where it is, in the non backed up loads panel. I was reading that you can wrap a CT around two wires as long as they are the same phase.

If I move it to right up against the main meter, do I need to get 400amp CTs? What is the downside of having 200amp CTs and the current hitting 220,230,250 amps potentially a couple times per year? Do they become inaccurate or explode?

While the CTs aren't likely to blow up, but that isn't to say that the electronics on the other end, the Gateway, won't. If you need the higher current rating, I would get the right equipment rather than risk letting the magic smoke out.

 

[mongo]

Second PV inverter is staying where it is, in the non backed up loads panel. I was reading that you can wrap a CT around two wires as long as they are the same phase.

If I move it to right up against the main meter, do I need to get 400amp CTs? What is the downside of having 200amp CTs and the current hitting 220,230,250 amps potentially a couple times per year? Do they become inaccurate or explode?

You can run multiple wires through one CT if they fit. Issue with over range depends on the measuring device. Ideally, it would just saturate at a high reading, but it's situation dependent.

 

[wwhitney]

Utility meter brings 200amp service into non-backed up load panel with 200amp main breaker and 225 amp rated bus bar. This panel has the car charger and my second solar inverter in it. Lugs come out of the bottom and go to my battery gateway and behind that is my primary inverter, 2 Powerwalls, and my main house panel.

Ohio still uses the 2017 NEC, which has a bit of a blind spot in the rules on protecting busbars (705.12(B)), as it does not address feed-thru lugs. I'm assuming that the lugs on the bottom are at the opposite end of the bus as the main breaker. If so, the above setup could allow excess current on the service panel busbar, depending on the details of what loads are in that panel.

What's the reason the secondary inverters isn't behind the GW? Grouping the secondary inverter interconnection with the primary interconnection and the connection of the PWs could alleviate the issue, depending on the GW configuration.

Cheers, Wayne

 

[supratachophobia]

Where is second PV inverter going?
Yeah you move the CTs to either pre-meter, around both cables on the feeds, or two CTs per phase. Need to check their measurement range and inner diameter.

Gen 3 WC will power share without extra wiring, but I grok the desire for more capacity.

Second PV inverter is staying where it is, in the non backed up loads panel. I was reading that you can wrap a CT around two wires as long as they are the same phase.

If I move it to right up against the main meter, do I need to get 400amp CTs? What is the downside of having 200amp CTs and the current hitting 220,230,250 amps potentially a couple times per year? Do they become inaccurate or explode

Ohio still uses the 2017 NEC, which has a bit of a blind spot in the rules on protecting busbars (705.12(B)), as it does not address feed-thru lugs. I'm assuming that the lugs on the bottom are at the opposite end of the bus as the main breaker. If so, the above setup could allow excess current on the service panel busbar, depending on the details of what loads are in that panel.

What's the reason the secondary inverters isn't behind the GW? Grouping the secondary inverter interconnection with the primary interconnection and the connection of the PWs could alleviate the issue, depending on the GW configuration.

Cheers, Wayne

Powerwall documentation has a max amount of DC input allowed for each Powerwall (their wording, not mine). They have a limited charge rate and they have no "smart" method to tell the inverters to power down. So the way they regulate their input is to ensure that maximum solar power can't exceed their charge rate. I feel like it's 7kw per Powerwall. And I have a 10k and 7k inverter.


I will check and see if the bottom logs are on the bus bar or have there own connection to the main breaker for that panel.

Thank you for the reply.

 

[mongo]

Powerwall documentation has a max amount of DC input allowed for each Powerwall (their wording, not mine). They have a limited charge rate and they have no "smart" method to tell the inverters to power down. So the way they regulate their input is to ensure that maximum solar power can't exceed their charge rate. I feel like it's 7kw per Powerwall. And I have a 10k and 7k inverter.


I will check and see if the bottom logs are on the bus bar or have there own connection to the main breaker for that panel.

Thank you for the reply.

My understanding is the Powerwalls raise line frequency and/or voltage to cause PV inverters to reduce output (when in island mode). Inverters, at a minimum, self disable when the grid is out of range. Fancier ones can reduce output proportionally based on grid offset.

 

[wwhitney]

Powerwall documentation has a max amount of DC input allowed for each Powerwall (their wording, not mine). They have a limited charge rate and they have no "smart" method to tell the inverters to power down. So the way they regulate their input is to ensure that maximum solar power can't exceed their charge rate. I feel like it's 7kw per Powerwall. And I have a 10k and 7k inverter.

Assuming your two years of data accurately covers both inverters and your house loads, you could download the data and calculate for each interval "PV generation - house loads" and find the max positive value of that.

Because the issue with having too much PV behind the GW is that when the grid is out, the PWs have to soak up all the excess PV that is not going to your house loads. So if the maximum charge rate for 2 PWs is 10 kW continuous (IIRC), if you're off-grid and the excess PV is over 10 kW, the GW has to knock the PV off-line. [Or maybe try to dial back the PV output, if your PV inverters are "fancier" as mongo put it, and if the GW behaves appropriately.] Of if you are at home and aware this possibility may be happening, you could turn turn on some loads to reduce excess PV.

What non-back up loads do you have in the service panel? If it's only a handful of double pole breakers that add up to less than 225A, then the concern about feed-thru lugs is academic in practice (although the allowances in the 2020 NEC that cover feed-thru lugs aren't written so broadly, so it might still not comply with the 2020 NEC, although that's not important for you).

Cheers, Wayne