F150 lightning pricing is live

[danrjones]

Ok, I think I see what you are saying, NEC only counts power sources toward the busbar max, not loads.

I know that when I did my solar I was limited on my solar size due to the busbar maximum, I maxed out my busbar at 120%, and the inspector would not have approved a higher kW system.

Which is probably way overkill, as the chance I'm pulling 200 amps from the grid AND using all my solar all at once is NIL.

 

[goldbrick]

I know that when I did my solar I was limited on my solar size due to the busbar maximum, I maxed out my busbar at 120%, and the inspector would not have approved a higher kW system.

I swapped my 200A main breaker for a 150A main breaker due to this. When I bought the panel I thought 'bigger is better' but then when I installed the solar system I had to rethink that approach.

 

[danrjones]

Yes its an interesting subject, where you may be forced to de-rate your main breaker for the panel. I get why they do it, you can have 400 amps worth of breakers in a 200 amp panel, but the bus bar is still protected - if you ever did use more than 200 amps on your multiple breakers, you trip the main. And, as I discovered with my panel, the bus bar is usually (always?) rated for more than your main breaker, so their is safety margin built in. But "in theory" you could be using 200 amps through the main and say 50 amps of your solar, thereby having 250 amps going across your bus bar.

But, when I added a 6.4 kW DC system (6 kW AC), that meant 6,000 Watts / 240 = 25 amps, so I think they required a 40 amp breaker - I don't think I used a 30, but I'd have to go back and look. My older system was 3 kW AC, which is 12.5 amps but its under a 20 amp breaker. The inspector used the breaker size, which meant I really was no where near the bus bar limit, not really. Assuming my busbar is rated for 225, with 225 x 1.2, that limits me to 270 amps. Maybe my busbar is 220... can't remember, I just know it was slightly higher.

 

[wwhitney]

The present version of the rule uses 125% of the inverter output current, rather than the breaker size, which may be rounded up.

So if you have a service panel that with a 225A bus and a 200A main breaker, you can put a PV breaker at the opposite end of the bus, and it can be connected to inverters of up to (1.2 * 225 - 200) / 125% = 56A of output current, or 13.4 kW @ 240V.

Cheers, Wayne

 

[SageBrush]

I think the rule is that your branch circuits can't add up above 120% of your panel and bus bar rating.

It's not all your branch circuits, almost all of which are loads, it just applies to sources of power when there are multiple sources.

That makes sense to me, although I understood the rule as did Dan -- meaning count up the breakers on the busbar and do not exceed 120% of its rating.

Do you have a NEC reference handy ?

When I installed PV, I added a 200 Amp (main breaker and busbar) load center. I swapped out the main breaker for a 150 Amp, specifically so that I could add a 40 Amp breaker for incoming PV and not exceed 1.2x of the overcurrent protection.

 

[wwhitney]

Do you have a NEC reference handy ?

Yes, (2017) NEC 705.12(B) or (2020) NEC 705.12. Here's a link to the former, in the form of California's current electrical code, they have not amended that section:

https://up.codes/viewer/california/ca-electric-code-2019/chapter/7/special-conditions#705.12_(B)

Cheers, Wayne

 

[goldbrick]

I should add that in my case, my (outdoor) service panel has the main breaker and only 1 other breaker - a 30A breaker for the solar panels on my roof. From this panel there are wires feeding a main-lug panel in the basement which (while technically a sub-panel) holds all the breakers for the circuits in the house.

My main concern was with the ampacity limit on the wires from the service panel to the sub-panel, although I have to admit that I thought the buss bar would also be an issue. Apparently it isn't with my current solar output and I'm surprised by how the buss bar limits are calculated.

As always, thanks Wayne for sharing your expertise.

 

[wwhitney]

I should add that in my case, my (outdoor) service panel has the main breaker and only 1 other breaker - a 30A breaker for the solar panels on my roof. From this panel there are wires feeding a main-lug panel in the basement which (while technically a sub-panel) holds all the breakers for the circuits in the house.

If you shut off the "main breaker" does the solar inverter keep running, per the meter?

Typically in a panel like you described, the two breakers are in parallel, and you effectively have two different service disconnects. In which case none of the above discussion applies to your configuration, you have what is known as a "line-side" interconnection, and the 120% rule and similar requirements do not apply. Any electrical power going to your subpanel has to pass through the "main breaker", whether it comes from the PV or the utility. So the feeder and subpanel only have a single source of power.

Cheers, Wayne

 

[Marktm]

It does appear that the extended battery version of the Lightning is quite specialized with the requirement for the Charge Station Pro being installed to support "overnight" charging. Quotes from a DesignNews article:

- “In order to get the overnight charging we needed, we installed dual chargers as well as upped the amperage of that wall box to be able to deliver 80 amps of service and get a lot more power through there so we can charge the battery quicker and get overnight to full,”
- "The robust power connection works both ways, so the truck can send more power to the house through the wall box in the event of a power failure."

My assumptions are (if anyone can confirm/correct?):
- It is a J-1772/DC combo (CCS) connector as part of the Charge Station Pro
- The two AC/DC on board chargers are 40 amps (240 VAC) each capable
- Maybe One of the inverter/on board chargers are bi-directional and can feed back 40 amps to the Charge Station Pro (the 9600 watt backup power rating => 40*240=9600).

This is where I cannot make sense to "assume" that the Charge Station Pro can provide any type of seamless "backup" power unless there is a built in grid sensor/transfer system. Seems there is need for either a separate subpanel to transfer to, or a separate grid disconnect that is opened by the grid sensor so that the home and/or construction panel can be safely energized to provide such power. A simpler approach might be to provide a more typical "RV" power receptacle on the Charge Station Pro to act as a typical generator.

Anyone have more details on the "backup" system?

 

[knightmb]

This is where I cannot make sense to "assume" that the Charge Station Pro can provide any type of seamless "backup" power unless there is a built in grid sensor/transfer system. Seems there is need for either a separate subpanel to transfer to, or a separate grid disconnect that is opened by the grid sensor so that the home and/or construction panel can be safely energized to provide such power. A simpler approach might be to provide a more typical "RV" power receptacle on the Charge Station Pro to act as a typical generator.

Anyone have more details on the "backup" system?

Until someone has one installed, we are all guessing I'm afraid.

My take, it probably uses a main disconnect to isolate the house from the utility service. Then once that is done, the EV can just back-flow the battery to the 240V AC and that basically powers the house. That would be a simpler approach than trying to have yet another device somewhere that needs to automatically switch around power sources. Basically, the Truck can have 240V AC feed into it, it functions for charging. If the power is out, the charger works in reverse to convert the battery voltage back out the same connection for 240V AC and since it's already wired into the main box, the house comes back to life. Basically the same way someone would wire in an emergency generator to run a house. Over simplified explanation of course, but anything else just gets more expensive and complicated.

 

[SageBrush]

The present version of the rule uses 125% of the inverter output current, rather than the breaker size, which may be rounded up.

So if you have a service panel that with a 225A bus and a 200A main breaker, you can put a PV breaker at the opposite end of the bus, and it can be connected to inverters of up to (1.2 * 225 - 200) / 125% = 56A of output current, or 13.4 kW @ 240V.

Cheers, Wayne

IF I am reading 705.12(B)(3) correctly, we can choose any of three different calculations. Presuming a 200 Amp main breaker and 200 Amp busbar, the second choice says:

Multiply the busbar by 1.2. So e.g. in the case of a 200 busbar, we would start with 240 Amps allowed in the busbar
Subtract the busbar main breaker, so 40 Amps remain
The additional power source can be 40*0.8 = 32 Amps output

 

[danrjones]

The present version of the rule uses 125% of the inverter output current, rather than the breaker size, which may be rounded up.

So if you have a service panel that with a 225A bus and a 200A main breaker, you can put a PV breaker at the opposite end of the bus, and it can be connected to inverters of up to (1.2 * 225 - 200) / 125% = 56A of output current, or 13.4 kW @ 240V.

Cheers, Wayne

IF I am reading 705.12(B)(3) correctly, we can choose any of three different calculations. Presuming a 200 Amp main breaker and 200 Amp busbar, the second choice says:

Multiply the busbar by 1.2. So e.g. in the case of a 200 busbar, we would start with 240 Amps allowed in the busbar
Subtract the busbar main breaker, so 40 Amps remain
The additional power source can be 40*0.8 = 32 Amps output

That's exactly how the inspector did mine about 1.5 yrs ago for my newer system. Only difference is that I had a bus bar rated for slightly over 200 amps allowing a 20 and a 40 breaker for solar.

Both of my solar systems shut down if I disconnect from the grid. The newer system also required individual DC disconnect modules for each panel - only allowing about 1 volt each until the inverter tells them to turn on. Rapid shutdown is what was required.

 

[wwhitney]

IF I am reading 705.12(B)(3) correctly

Yes.

Wayne

 

[Marktm]

My take, it probably uses a main disconnect to isolate the house from the utility service. Then once that is done, the EV can just back-flow the battery to the 240V AC and that basically powers the house. That would be a simpler approach than trying to have yet another device somewhere that needs to automatically switch around power sources. Basically, the Truck can have 240V AC feed into it, it functions for charging. If the power is out, the charger works in reverse to convert the battery voltage back out the same connection for 240V AC and since it's already wired into the main box, the house comes back to life. Basically the same way someone would wire in an emergency generator to run a house. Over simplified explanation of course, but anything else just gets more expensive and complicated.

This discussion likely requires a separate topic - and certainly OK with me. I'll only consider the Lightning (with the "Pro" stuff) if the battery energy can be used for V2X functions that include energy arbitrage with the grid, solar energy integration and seamless home emergency backup (auto transfer). As evidenced by the current discussions around the main panel sizing, this will require careful designs with code implications.

It's just my guess, but from their confusing statements (quoted earlier), that they will provide some type of 40 amp capable connections(?) that will be energized ONLY if the grid is down while charging and always available when not connected to the grid. It will then be up to the user to determine how best to set up the "backup" and/or remote use.

Again, does anyone have more information?

 

[goldbrick]

If you shut off the "main breaker" does the solar inverter keep running, per the meter?

No. I'm using the Enphase micro-inverters connected to the load-side and they handle all the disconnect requirements. If the grid goes down, my solar output = 0.

 

[wwhitney]

No. I'm using the Enphase micro-inverters connected to the load-side and they handle all the disconnect requirements. If the grid goes down, my solar output = 0.

Yes, I understand that. But you said your service panel has just two breakers. The point of my question was that such a panel could internally be configured in two different ways. The breakers could be in parallel (in which case they are typically side by side, and there probably is no room for a third breaker). In that case shutting off one breaker does not interrupt power to the other; if you leave the solar breaker on, and shut off the other breaker, your interior subpanel would lose power, but the solar inverters would not.

So looking at the meter in that configuration on a sunny day would tell you whether that is the case. The meter will either show 0 kW or will show your solar export to the grid.

Or the two breakers could be in series. In that case the non-solar breaker really is a main breaker and would kill power to the solar. But that would typically only be the case if the panel had room for multiple other breakers next to the solar breaker, and the main breaker is separately located, often at the top. And the panel would then presumably have feed-through or subfeed lugs to supply the interior panel.

The rules on busbar protection for PV interconnection are different for the two cases. Everything I've written is based on the second case, but your setup sounds like the first case.

Cheers, Wayne

 

[goldbrick]

I think I see what you mean. My service panel has 1 main breaker and 8 spaces. It is feeds a sub-panel out the bottom.

I've used 2 of the 8 available spaces for a 240V breaker that is fed by the solar inverters. So it currently has the main breaker and one double-pole breaker.

I'm planning to also feed a sub-panel in the garage from this panel and maybe a heat pump but I haven't gotten to that yet.

 

[wwhitney]

I think I see what you mean. My service panel has 1 main breaker and 8 spaces. It is feeds a sub-panel out the bottom.

That kind of panel is pretty tricky to apply 705.12(B) to properly. It presumably has feed-through lugs at the bottom with the main breaker at the top. So it has a bus connection without OCPD for the feeder. Up through the 2017 version, the NEC was silent on how to treat those panels for PV interconnection; the conservative assumption is that you can't use the 120% on such a panel. That's because the feed-through lugs are at the end of the bus opposite the primary supply, so the PV breaker can't be placed at the opposite end of the bus, as required by the 120% rule.

The 2020 NEC introduced some language in 705.12(B)(3)(6) to address feed through lugs, but I find the new language unclear. Your subpanel definitely needs a main breaker in it, and of course the feeder from the service panel to the subpanel is only protected by the service disconnect, so it needs to be sized accordingly. But then as long as that feeder doesn't have any other panels or PV interconnections on it (the feeder is point-to-point), in practice applying the 120% rule to your service panel will provide the same level of busbar protection as it would to a panel that doesn't have feed-through lugs, regardless of what 705.12(B)(3)(6) says.

Cheers, Wayne

 

[goldbrick]

Your subpanel definitely needs a main breaker in it

I don't have a main on the sub-panel. I've been researching this a bit since your comment and it looks like one of those 'gray areas' in the code that generate a lot of discussion. FWIW, it did pass inspection so I'll probably just leave it alone.

Some more details: the run from the feed-through lugs to the sub-panel < 10'. I used 3/0 Cu THHN-2 wire for the connection. The wires are in PVC conduit. Either one or all of those factors sufficed or my inspector just thought it was OK. I don't remember why I didn't use a panel with a main for the sub-panel but I do like having 'the breaker box' inside the house instead of outside as it was before.

Originally, when I put in the service entrance, there was nothing in the panel except the main. When I installed the solar I replaced the 200A main with a 150A main mainly due to the 3/0 feeders to the sub panel. Of course there is a separate AC disconnect for the solar system next to the service panel besides the fact that the inverters shut down without the grid. It all seems safe to me but now I'm wondering if I did everything as well as I could.

 

[wwhitney]

Originally, when I put in the service entrance, there was nothing in the panel except the main. When I installed the solar I replaced the 200A main with a 150A main mainly due to the 3/0 feeders to the sub panel.

OK, with a service panel that has a 200A busbar, and a 150A service disconnect, and a 40A PV breaker, and subfeed lugs, the service panel busbar is protected per the 100% rule. That option requires that the sum of the sources (150A + 40A, if you actually have 32A of inverter current on that 40A breaker) needs to be less than the busbar rating. In which case there is no restriction on the PV breaker location (unlike the 120% rule), so the presence of subfeed lugs is not an issue. You can add additional loads, and possibly inverters, but you need to keep the total inverter current not more than 40A.

Now, I thought that a panelboard with a single source of supply (the feeder from the subfeed lugs) required a single breaker protecting it, per 408.36. However, I see that Exception 2 allows 2 breakers instead. So I guess 408.36 is satisfied for the subpanel, again because 150A + 40A < 200A, the subpanel busbar rating. If you had brought both 20A microinverter circuits to your service panel, rather than combining them in a separate panel, you would have had a violation of 408.36 for the subpanel.

Anyway, seems like you threaded the needle and the configuration complies with the NEC.

Cheers, Wayne