rapid-shutdown requirement for ground-mount system with inverter in dwelling

RustyShackleford

Senior Member
Location
NC
I am installing a ground-mount system; generally these do not require rapid-shutdown (subject to 2017 NEC). However, the inverter will be located inside the house (in a utility room next to the main panel). This means there will be one or more wire pairs carrying up to 600vdc coming into the utility room. The wiring will be done underground in Sch80 PVC conduit. My main concern is reading an interpretation of the NEC that "conductors that extend greater than 10 ft from the array (outside) or more than 5 ft inside a building are required to be de-energized upon command of shutdown." It's the "5ft inside a building" that concerns me. Does this mean that the distance the wiring runs from where it penetrates the building envelope to where it enters the inverter must be 5ft or less ? Even if said wiring is contained in conduit ?
 

jaggedben

Senior Member
Either the distance must be less than 5ft, or you must have a switch installed outside where the wiring enters, along with appropriate signage to direct fire fighters to it.
 

RustyShackleford

Senior Member
Location
NC
Either the distance must be less than 5ft, or you must have a switch installed outside where the wiring enters, along with appropriate signage to direct fire fighters to it.
So I'm covered as far as the "10ft from the array outside", because the DC conductors are going to go straight down into the ground in conduit.

But once I get inside the dwelling, even if the wiring is protected in conduit, it must be no more than 5ft, horizontal run plus vertical run. If I can't manage that, it must have the switch with the rapid-shutdown signage.
 

jaggedben

Senior Member
You've got it.

The 10ft part is not relevant here because presumably the wiring within 10ft of the array is not on a building.
 

RustyShackleford

Senior Member
Location
NC
The 10ft part is not relevant here because presumably the wiring within 10ft of the array is not on a building.
Right, because it's coming down one of the posts supporting the ground-mount installation. There may be some storage under the panels - trash cans, bicycles, and the like - but I don't think that'll make it a building.

As far as the 5ft inside the dwelling, it's very close. And I guess using conduit doesn't help me (it'd need to be in conduit anyhow). The horizontal run would be in the crawlspace (which I fear counts as "inside"), and then just come up thru the floor a couple of feet into the inverter's housing.

As an aisde, I'd be happy to implement rapid shutdown, but as suspected and just confirmed in a call with Tigo, it is currently impossible to support 2017 rapid-shutdown requirements and have the secure-power outlet (SPS) still functional. Because the rapid-shutdown must cause the TS4 MLPE devices to stop generating DC current. They will actually disable this if you fill out a form, but that involves assuming some serious liability.
 

wwhitney

Senior Member
Location
Berkeley, CA
As far as the 5ft inside the dwelling, it's very close.
Then (2014) 230.6(2) may help you. If you are just over 5 ft, measure back 5 ft from the equipment, and encase the conduit in 2" of concrete from that point onward. If it is only a foot or two of conduit, could be your easiest solution.

Cheers, Wayne
 

RustyShackleford

Senior Member
Location
NC
Then (2014) 230.6(2) may help you. If you are just over 5 ft, measure back 5 ft from the equipment, and encase the conduit in 2" of concrete from that point onward. If it is only a foot or two of conduit, could be your easiest solution.
Wow, ok, that's an option; guess that article doesn't allow special conduit of case-hardened steel :)

Thinking now that the best answer is to put the inverter with the panels. Inverter installation manual (SMA SunnyBoy -41 series) states "The product is suitable for indoor and outdoor use", which I guess means it can be fully-exposed to weather, though I can shelter it quite a bit better under the panels (even though it is evidently impossible to create a rain-tight roof with panels). Then route the AC to the utility room in the house (buried UF-B or THHN in conduit). I don't believe I have to worry about the 5ft then, because when AC is disconnected (via a breaker, or pulling the meter), that AC line (from inverter to panel) will be de-energized (any modern grid-tied inverter does that, for anti-islanding).

The "secure power" outlet would then be at the panels (unless I put it through the conduit too), instead of in the utility room.
 

pv_n00b

Senior Member
Location
CA, USA
As an aisde, I'd be happy to implement rapid shutdown, but as suspected and just confirmed in a call with Tigo, it is currently impossible to support 2017 rapid-shutdown requirements and have the secure-power outlet (SPS) still functional. Because the rapid-shutdown must cause the TS4 MLPE devices to stop generating DC current. They will actually disable this if you fill out a form, but that involves assuming some serious liability.
This is where your RSS initiation device is important. If you are using the loss of grid AC as the initiation device then that takes out any backup options from the system. If you want backup options then you need to use an external switch as the initiation device and not loss of grid AC. In your case, you will want a manual controller for the Tigo RSS Transmitter and not let it be controlled by loss of AC.
 

RustyShackleford

Senior Member
Location
NC
This is where your RSS initiation device is important. If you are using the loss of grid AC as the initiation device then that takes out any backup options from the system. If you want backup options then you need to use an external switch as the initiation device and not loss of grid AC. In your case, you will want a manual controller for the Tigo RSS Transmitter and not let it be controlled by loss of AC.
Yes, I should re-state my assertion you quoted: it is currently impossible to have the secure-power outlet (SPS) functional during grid outages, without having another plan for dealing with rapid shutdown, because the panels and/or optimizers must continue to generate DC for SPS to work.
 

RustyShackleford

Senior Member
Location
NC
Yes, I should re-state my assertion you quoted: it is currently impossible to have the secure-power outlet (SPS) functional during grid outages, without having another plan for dealing with rapid shutdown, because the panels and/or optimizers must continue to generate DC for SPS to work.
Actually, I've come to believe that this may nor be true. I think SMA knows it's a problem and plans to release new firmware to handle it in the -41 models.
 
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