Remote power off vs knife disconnect

[n2aws]

I've been scouring the NEC (2017 in my area still) for an answer to this.

My inverters support "remote power off" by just completing a circuit between two pins. This immediately shuts the inverters down, and kills all A/C power to the critical loads panel.


In addition to that, my panels on the roof are equipped with Tigo RSD modules that, when they stop recieving the heartbeat, initiate the RSD. The device that sends the heartbeat is plugged into an outlet that is fed from the critical loads panel (that again, loses power when the inverter RPO feature is activated.

Under NEC 2017, does this satisfy the requirements/replace the need for a knife disconnect?


I've also called my AHJ with this question, but all they would say is "Most people use a knife disconnect" which doesn't actually answer my question. Most people are also using microinverters these days, AND don't have batteries/critical loads panel, so that answer is less than helpful.

The only thing the AHJ has actually *answered* for me, is that they still use NEC2017, with no other local requirements with 1 exception.. For roof setbacks, they don't require 2 36" edges leading up the roof. They only require a single 36" walkway.

Anyway, anyone intimately familiar enough with NEC2017 to say difinitively if I can use RPO in place of a knife disconnect (bonus if you can point me to the section, so I can show it to an inspector if needed?)

 

[pvgirl]

Even with RSD there are still requirements for disconnects to enable isolation of the equipment. Code doesn't require knife switches, but some compliant form of disconnect is required. In addition many utilities require a lockable disconnect beyond what code requires.

Which disconnect are wanting to eliminate?

 

[n2aws]

Even with RSD there are still requirements for disconnects to enable isolation of the equipment. Code doesn't require knife switches, but some compliant form of disconnect is required. In addition many utilities require a lockable disconnect beyond what code requires.

Which disconnect are wanting to eliminate?

I'm not planning on doing any NEM agreements or anything, so the utility isn't involved. This should "just" be NEC2017 for the local AHJ, from my understanding. (My understanding is, the utility would have some say if I were selling back to the grid, but thats not the plan)

The knife disconnect would likely have been between the inverter, and the protected loads panel. If it matters, the protected loads panel is on the outside of the house, and the emergency power off button for the solar is going to be within 2' of that same panel. I guess the only part that I'd be missing, would be that the emergency switch I was planning to use doesn't have a lockout. But, I can likely just find another emergency switch that does.

Heck, by rights.. the protected loads panel itself has a spot for a padlock. the fire dept could flip the breaker in the panel, and then lock it out that way, once again (in my mind) eliminating the need for a knife disconnect.

 

[pvgirl]

Without a net metering agreement the utility probably won't be aware, but if it's utility interactive inverter and it's connected to there grid they could require a disconnect, although they would want it on the grid input side of the inverter.

Some form of disconnect and over current protection will be needed on AC input and output of the inverter. As well as a DC disconnect for PV sources. 705.22 Includes a requirement that they be lockable in the off position, this could be disconnect with a lockable handle, or a circuit breaker with am approved locking hasp permanently attached.

Do you have a source or code reference for this requirement of knife switch?

Also note NEC 2017 has been amended in many states so there may be changes that only apply in your state.

 

[n2aws]

Without a net metering agreement the utility probably won't be aware, but if it's utility interactive inverter and it's connected to there grid they could require a disconnect, although they would want it on the grid input side of the inverter.

Some form of disconnect and over current protection will be needed on AC input and output of the inverter. As well as a DC disconnect for PV sources. 705.22 Includes a requirement that they be lockable in the off position, this could be disconnect with a lockable handle, or a circuit breaker with am approved locking hasp permanently attached.

Do you have a source or code reference for this requirement of knife switch?

Also note NEC 2017 has been amended in many states so there may be changes that only apply in your state.

Both AC input and output have breakers.

grid input has a 60a breaker in the main panel, as well as a 60a breaker in the PDP.
The output has a 60a breaker in the PDP, and potentially a 60a breaker in the critical loads panel (it's a main lug only panel, but I can add a breaker if needed)

The remote power off wouldn't disconnect AC power on the grid side specifically, but when triggered the inverter shuts off completely, meaning that it'd be disconnected. This is the crux of my dilemma. In my mind, this alone would negate the need for the knife disconnect as long as I use a lockable switch as you suggested. However, I'm trying to find anything in the NEC that supports this "theory"

On the state level, I'm in Florida. I don't *think* we have anything at the state level that overrides or supplements NEC, and my AHJ has said they don't do anything "above and beyond" the NEC. so, I think I'm good there.

 

[Hedges]

I think your RPO is good enough for firemen.

I think utility should be informed about equipment operating in parallel with their grid (e.g. zero export), but not equipment isolated by a transfer switch.

I think visible blade knife switch is a utility requirement so they can be certain there is nothing backfeeding the grid when linemen are working on it. In practice they have never turned mine of. They now say it is optional; they could yank the meter instead. The knife switch was between my breaker panel and my inverters.

When working on wiring that connects to the grid there should be an "isolator", a breaker with 1" gap between contacts. That is distinct from "supplementary protector" which looks and works like a breaker but doesn't provide as great a distance for isolation.

The RSD for fireman safety is an electronic gizmo, do doesn't seem like any particular safety switch is required.

What I'll be doing is using either a 3-pole knife switch or a microswitch for handle position of 2-pole knife switch to shut down RSD. If straight GT PV, simply removing grid AC would trigger it, but with AC coupling to battery inverters I need the 3rd switch. One handle will isolate from grid and trigger rapid shutdown. Circuit breakers will let me remove grid AC without triggering RSD.

 

[pvgirl]

As long as one of the breakers on the input and output have a hasp for locking in the off position you should be good to go. Example of a locking hasp: https://www.amazon.com/Square-Schneider-Electric-Breaker-Accessories/dp/B009OYAL0M you will need to find the right one for the breakers you are using.

 

[Quattrohead]

My solar plans from Greenlancer do not have any knife disconnect, but I will be fully off grid no FPL to the property.
I specifically asked GL and they removed the knife disconnect when I pondered if the RSD system was good enough on its own.

 

[n2aws]

My solar plans from Greenlancer do not have any knife disconnect, but I will be fully off grid no FPL to the property.
I specifically asked GL and they removed the knife disconnect when I pondered if the RSD system was good enough on its own.

Good to know.

Curious, what part of FL?

I'm in southwest florida

 

[Quattrohead]

Good to know.

Curious, what part of FL?

I'm in southwest florida

Central East Coast Florida, Brevard county.

 

[AllClear]

My inspector is beating me up right now saying that I must have a knife switch & that the lockable circuit breaker I have isn't sufficient to meet utility requirements. My utility said they are not aware of a knife switch requirement. The inspector used 705.20 as a reference for the violation.

Snip from the 2020 NEC, 705.20 Disconnecting Means, Source.
The disconnecting means shall comply with the following:
(1) Be one of the following types:
(a) A manually operable switch or circuit breaker
I'm wondering if he used the wrong code reference, or is making stuff up.

The RSD devices you refer to that are required by 690.12 will not suffice for the disconnect required by 705.20

 

[n2aws]

My inspector is beating me up right now saying that I must have a knife switch & that the lockable circuit breaker I have isn't sufficient to meet utility requirements. My utility said they are not aware of a knife switch requirement. The inspector used 705.20 as a reference for the violation.

Snip from the 2020 NEC, 705.20 Disconnecting Means, Source.
The disconnecting means shall comply with the following:
(1) Be one of the following types:
(a) A manually operable switch or circuit breaker
I'm wondering if he used the wrong code reference, or is making stuff up.

The RSD devices you refer to that are required by 690.12 will not suffice for the disconnect required by 705.20

Thanks for the reference. I'll research the 2017 version of this and see if it looks like it'll force me to use a knife disconnect.

It's like.. I understand their caution, and why they want it.. but at the same time.. if I've got something that does the exact equivelant and is labelled as such, you'd think it'd pass. But, I realize that all inspectors are different.

 

[Hedges]

Guess you'll have to wait until the Supreme Court rules on the meaning of "or". I understand they are to shortly take up "and".

Until then, you're at the mercy of a bureaucrat.
If he isn't willing to understand plain English, you'll have to tee off to a safety switch. eBay can be a cheaper source.

RSD is not sufficient for disconnect (no backfeed to grid) but is sufficient or fireman safety.

 

[Quattrohead]

RSD is not sufficient for disconnect (no backfeed to grid) but is sufficient or fireman

But RSD turns off the inverter output, panel output and the batteries in EG4 case, so there is no power in the house, so it is safe.
The regs need to catch up with reality.

 

[Quattrohead]

My inspector is beating me up right now saying that I must have a knife switch & that the lockable circuit breaker I have isn't sufficient to meet utility requirements. My utility said they are not aware of a knife switch requirement

Your inspector needs to get his head out of his 1950s arse.