Whole home back up - a simple approach

[Henry Ford]

That does not address the continuous GEC requirement.

Agreed. I misunderstood what the exception was addressing.

After doing some reading I came across the following informational note in NEC 250.30.

Informational Note No. 1: An alternate ac power source, such as an on-site generator, is not a separately derived system if the grounded conductor is solidly interconnected to a service-supplied system grounded conductor. An example of such a situation is if the alternate source transfer equipment does not include a switching action in the grounded conductor and allows it to remain solidly connected to the service-supplied grounded conductor when the alternate source is operational and supplying the load served.

I believe this describes a Lightning plugged into a Generac 6853 which switches the hots and neutral but maintains the connection to the service ground. It seems to be describing this setup as code legal.

I'm not an electrician.

Edit: the above proves I'm not an electrician and is wrong. @v2h8484 explains below.

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[v2h8484]

Agreed. I misunderstood what the exception was addressing.

After doing some reading I came across the following informational note in NEC 250.30.

Informational Note No. 1: An alternate ac power source, such as an on-site generator, is not a separately derived system if the grounded conductor is solidly interconnected to a service-supplied system grounded conductor. An example of such a situation is if the alternate source transfer equipment does not include a switching action in the grounded conductor and allows it to remain solidly connected to the service-supplied grounded conductor when the alternate source is operational and supplying the load served.

I believe this describes a Lightning plugged into a Generac 6853 which switches the hots and neutral but maintains the connection to the service ground. It seems to be describing this setup as code legal.

I'm not an electrician.

You misunderstood again. "Grounded conductor" is the neutral wire which is definitely switched when a neutral switch is used.

Just FYI, however inconvenient the info I have shared is, it's been confirmed by the former electrical department head for 40 years at the Boston Garden where truck mounted generators (i.e. SDS) are used for various events and they always run a separate code compliant GEC.

 

[Henry Ford]

You misunderstood again. "Grounded conductor" is the neutral wire which is definitely switched when a neutral switch is used.

Just FYI, however inconvenient the info I have shared is, it's been confirmed by the former electrical department head for 40 years at the Boston Garden where truck mounted generators (i.e. SDS) are used for various events and they always run a separate code compliant GEC.

Indeed I have.

If what you are saying is true - I can't disprove it - a Lightning cannot be used as a backup generator while connected to a house under any circumstances. This seems wrong, on the other hand the owner's manual says...

WARNING: Do not connect any vehicle power outlets to any premises. This can create a backfeed to utility lines. Failure to follow this instruction could result in property damage, fire, electrical shock or death.

Unless, I find out otherwise I'd say don't use a Lightning as a backup power source. Kind of a bummer.

How does the HIS deal with the grounding problem?

 

[roadhouse]

This might be a stupid question, but...

Why would this scenario (essentially a battery backup) be required to adhere to the NEC code focused on generators, when there's specifically sections that relate to Energy Storage Systems that directly talk about battery storage systems (NEC 706)?

 

[Zprime29]

This might be a stupid question, but...

Why would this scenario (essentially a battery backup) be required to adhere to the NEC code focused on generators, when there's specifically sections that relate to Energy Storage Systems that directly talk about battery storage systems (NEC 706)?

Flat out guessing here, but I think Energy Storage Systems provide DC power whereas the truck is providing AC power (when from PPOB).

 

[JRT]

That ford response is a bot, or just a useless comms person.

 

[v2h8484]

a Lightning cannot be used as a backup generator while connected to a house under any circumstances.

I wouldn't go that far. Perhaps more inconvenient and/or costly. It could be code compliant by running a proper GEC or just use extension cords to run loads per NEC Section 250.34(B) (https://up.codes/s/portable-and-vehicle-mounted-generators). BTW, do you think running a bunch of extension cords is safe since it's code compliant? Or as safe as a non-code compliant setup with neutral switching transfer switch that at least has an actual connection to earth ground? Why do you think the 250.34(B) exceptions exist? I mention this because someone in the entertainment industry said his company has representation on the CMP for that code section that made sure the exceptions were made. For me, such info makes simplistic notions like "code compliant = safe" and conversely "non-code compliant = unsafe" questionable at best. The reality is more complicated.

 

[v2h8484]

How does the HIS deal with the grounding problem?

AFAIK, HIS is not a SDS. It has a floating neutral and the neutral is not switched.

 

[Howard_Scott_Warshaw]

Yes, works fine. Have it all inverters wired through Backup Interface, managed separately from main panel.

So the inverters synced with the truck as the "utility"?

 

[Howard_Scott_Warshaw]

That ford response is a bot, or just a useless comms person.

My guess is an intern. And they dun goofed.

 

[VTbuckeye]

Quick?? question: when I had solar and powerwalls installed we also upgraded our electric service from 100 amp to 200 amp. The new panel is in the garage and it only has circuit breakers for the new heat pumps and for a 100 amp sub panel (old main panel). Neutrals were separated in the old panel when it became sub panel. Would a generator plug from the lightning to the sub panel (with neutral not bonded to ground because it isn't at the service entrance and there is only one place where neutral and ground are bonded) work with ppob or would the GFCI on the truck still trip due to the ground neutral bond back at the main panel? This is mostly a curiosity/thought exercise because of the powerwalls backup. In the spring/summer/fall we produce enough solar power to power the house, but winter conditions with a prolonged outage could drain our powerwalls more than solar can restore.

 

[Johnif]

So the inverters synced with the truck as the "utility"?

Interters have batteries, so they form a grid themselves, while isolated from utility

 

[GDN]

How does the HIS deal with the grounding problem?

Completely different system. It doesn't use the PPOB inverters at all. It pulls the HV out of the pack and does the conversion elsewhere. None of this thread or most of the others apply to the HIS.

 

[Henry Ford]

BTW, do you think running a bunch of extension cords is safe since it's code compliant? Or as safe as a non-code compliant setup with neutral switching transfer switch that at least has an actual connection to earth ground?

I think extension cords are their own special kind of unsafe. How unsafe is dependent on who is running the extension cords. I think the same can be said for non-code compliant solutions involving generators.

Why do you think the 250.34(B) exceptions exist?

I'm not following. I don't see exceptions to 250.34(B). It appears you can use vehicle mounted generators to plug stuff into or if they have a floating neutral you can plug your your house into it.

For me, such info makes simplistic notions like "code compliant = safe" and conversely "non-code compliant = unsafe" questionable at best. The reality is more complicated.

I agree. However, my comfort level goes way down when discussing non-code compliant solutions on the internet. There's a pretty big delta between what I'm comfortable doing myself and what I'm comfortable advocating without full context. Code is a convenient reference point and a pretty decent proxy for "safe".

 

[v2h8484]

I'm not following. I don't see exceptions to 250.34(B).

250.34(B) specify the conditions for exception to the ground rod rule.

I agree. However, my comfort level goes way down when discussing non-code compliant solutions on the internet. There's a pretty big delta between what I'm comfortable doing myself and what I'm comfortable advocating without full context. Code is a convenient reference point and a pretty decent proxy for "safe".

No disrespect but your "proxy" sounds a like mental crutch for skipping critical thinking. The problem with mental crutches is that they are prone to hacks. Case in point, the neutral transfer switch without a separate EGC setup somehow got labeled as code compliant (the "hack") on this forum and I suspect that got most people to quickly but incorrectly think it's "safe". If something (e.g. safety) is important then it's best not to rely on mental crutches.

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