I'll be interested to see if the tech support was wrong. He indicated that the hold-down was only for up to 150A breakers backfed onto the bus.
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Required Safety devices NEC 2020 code Powerwall installation
- Thread starter CrazyRabbit
- Start date
Breakers whose bus connection prongs will be energized if lifted from the bus are required to be held down. So if you have service conductors connected to a breaker's screw terminals to backfeed an MLO panel, yes it would require a hold down.
Cheers, Wayne
The part number that Eaton tech support gave was the BRPHDBJ and the BRPHDBJ2 depending on which location the breaker would be located. However they indicated it was not compatible with breakers larger than 150. It would specifically not work with the BJ2200 or BJ2225.
I'd love to be wrong so when they install it take a picture please.
do you mean "prongs that are energized when lifted"?
like a generator back feed breaker is required to be held down? i was thinking the hold down was required so that the breaker could not be energized, allowing the generator to be turned on back feeding the grid and shocking a lineman. i would love to see someone start a generator while connected to the grid!
or if i was using a plug in breaker as a master breaker on a panel that doesn't have one, it would require a hold down kit?
or back feeding solar into a loads panel?
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So Tesla is using the the BR1224L400R panel for a generation panel, would the PW breakers be required to be held down?
Powerwall Breakers are not usually required to be held down, though County of LA down south and a couple other jurisdictions do require them.
Seems to me like an oversight in the text of 2017 NEC 705.12(B)(5), which is still present in the 2020 and 2023 NECs. 408.36(D) reads:
(D) Back-Fed Devices. Plug-in-type overcurrent protection devices or plug-in type main lug assemblies that are backfed and used to terminate field-installed ungrounded supply conductors shall be secured in place by an additional fastener that requires other than a pull to release the device from the mounting means on the panel.
While 705.12(B)(5) says:
(5) Fastening. Listed plug-in-type circuit breakers backfed from electric power sources that are listed and identified as interactive shall be permitted to omit the additional fastener normally required by 408.36(D) for such applications.
But I expect that a Powerwall operating in off-grid mode will still shock you if you pull the breaker off the bus. So 705.12(B)(5) should have language like "listed and identified as interactive in all operating modes" to cover hybrid inverters like this. To clear up this gray area.
Cheers, Wayne
Breaking the AC connection between Powerwall and Gateway in any mode will cease PW inverter operation. If you have a concern here you might want to dig into the UL 1741 interactive standard to understand if this is an oversight in the standard, or if UL is already checking this for systems like the Powerwall. I am curious as well.
I suspect that since the PW cannot function without the Gateway, it is listed and tested as if both devices are present. For other systems I am not as familiar with, you may be correct in your concern. Since the Code cannot know what tech you are using, your point seems valid, assuming this is not written into the UL1741 standard already.
I agree that grid-forming inverters do need some safety check or a retainer on the breaker to prevent this shock hazard. If it is not written into the standard, maybe a PC is appropriate.
Have you experimentally verified this? What is the control mechanism used, i.e. how does it do that?
For that matter, when multiple PWs are running off-grid, how do they interact--is one of them running as a grid forming inverter, while the others stay in grid following mode? If that's the case, I could see it working as you describe. The Gateway and the grid forming PW would just need a protocol for confirming that the Gateway's local side of the MID is seeing the AC the grid forming PW is creating.
Cheers, Wayne
You pose a good question I could not answer because I didn't fully know. I could turn off my main breaker, then one of my 5 powerwall breakers and verify for myself. (goes and verifies)
Interesting result, and you are right again Wayne. If a system was in backup mode, any single breaker disconnected from the bus (or turned off) is still live from the Powerwall end of the circuit. I just tested with my system in backup mode, and turned off individual breakers. There was still 240 vac being created at the Powerwall side of the turned off breaker.
This is interesting and good to know, that unless all of the Powerwall are shutdown at once any number shutdown that is less than the total could remain energized from the Powerwall end of the circuit, despite a breaker in the off position.
Slightly disturbing, and one more reason why adding a button to shut all of them down at once is much better. I did confirm that this button trips the internal relay and disconnects all ungrounded conductors in the Powerwall(s).
I have to say now that I was wrong, and I think the Powerwalls need a breaker retainer as well, though I still think the code doesn't require them. Good thing the Gateway 2 internal panelboard retains the breakers as a standard.
Not sure what the retaining clip looks like for the BR1224L400R but I think it is designed to be at one of the 4 corners of the distribution bus, at least that's what my notes say. It could be there is a different retainer for a 30A breaker besides the BRPHDBJ2 and the BRPHDBJ needed for larger breakers depending on where on the bus they are located.
Yes, that's what he just said in the previous post. At least for the case of turning off just one of several PWs.
Edit: misread the question. In grid following mode the PWs surely deenergize their outputs when disconnected.
Cheers, Wayne
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Wayne,
I'm not sure that's what he said. I assume "backup mode" means off-grid.
On my system during normal on-grid operation, turning off one PW breaker cuts power from that PW, and there is no voltage on the wires to the breaker.
I can see how this works. But in the case of off-grid, the opposite would occur. How could the PW itself know that the breaker is off. Would just appear as no-load since the PW is grid forming in that case.
Either way, hold downs for the PW breakers should be required.
Yes, sorry, I misread CrazyRabbit's question. When operating in grid following mode (i.e. not off-gird) disconnecting a PW from the grid surely causes it to deenergize its output. I say surely because I've not tested it, but that has to be what the standard requires.
Cheers, Wayne
The way I suspect it works is that the voltage sense is in the GW2. So if a breaker disconnects all of your Powerwalls at once in off-grid mode, then the gateway senses this and turns the Powerwalls off.
Um, won’t the Gateway itself lose power if the grid disconnect switch is open and all the PowerWalls have their breakers open?
I think Vines is talking about the condition where only some of the PW breakers is opened; so presumably the Gateway is still energized from a second Powerwall.
I guess it's a good thing I got so many disconnecting means everywhere in my garage...
Exactly, or some crazy people with 9-12 Powerwalls and they are all spread out around the house to avoid fire code issues.
The issue at hand is that unless there is a single disconnect for all PW to gateway connections, any number of Powerwall disconnects could be turned off, but leaving just 1 Powerwall connected and the whole system may be energized from that remaining Powerwall. This would be especially bad when the Powerwalls breakers are perhaps not all landed in the same subpanel due to the location of new Powerwalls in a system that is expanded on.
This would be actually pretty easy to walk into and get shocked if an ordinary electrician was trying to replace a 30A Powerwall breaker. Maybe the extra screw or 2 in the breaker retainer would save them from themselves.
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