Solar PV disconnect

[Jesse7623]

I am on a job where the solar PV contractor is telling me that I need to install a disconnect near the meter to open one leg of the solar PV system. I guess they are saying that in their experience the power company likes to be able to have the confidence that they really turned off the power when they pull the meter, and the only way they can be sure is to have a disconnect just for the solar PV.
But as far as I know every UL listed Solar PV inverter has a built in relay that opens when it no longer senses power on the line side of the inverter.
I checked art. 690 briefly and cant seem to find anything requiring this disconnect. Maybe its a local AHJ issue or maybe I am really blind.

Thanks

 

[tallgirl]

UL1741 -- the anti-islanding requirements. They don't apply to all inverters, but they do apply to all the ones that can sell power back to the grid.

 

[Jesse7623]

Ok so what I gather from that Doc. is that it is still up to the local utility and Electrical inspector. Right?

 

[Sierrasparky]

I also understand it is a requirement of the fire dept.
If you have dogs I undestand that some require that they need to be able to turn the power off within reach without getting near the dogs.

The interesting think is that during daylight times the PV panels are making power regardless of the inverter. If there is a fire the panels are a potential hazard on the roof.

 

[jaggedben]

Jesse7623Ok so what I gather from that Doc. is that it is still up to the local utility and Electrical inspector. Right?

Yes, pretty much. (State codes may come into play as well.) The NEC only requires that there be a readily accessible disconnect, not that it be accessible from the exterior of a property. Requirements for disconnects accessible from the exterior of a property are not really an anti-islanding issue. Mostly they are fire department requirements, but I think that utilities also believe they have an interest in being able to turn off PV systems.

Large amounts of PV feeding back to the utility systems could cause technical problems. Up till now PV is still not really common enough to cause such problems but it's possible that this will change. Moreover, if the utility needs to do repair work (replace a transformer, say), I bet they would like to re-energize the lines and make sure things work without a whole bunch of backfeed, before everyone's PV kicks in. I would say there are also potential billing issues where the utility would like some physical control of the PV output. I'm only guessing at their motivations but these seem likely. Bottom line, they don't want to give up control of what is feeding energy to the grid.

the power company likes to be able to have the confidence that they really turned off the power when they pull the meter

I think you misunderstood one detail. They want a way to ensure the PV output to the grid is off without pulling the meter, and/or without shutting down utility power to the property.

 

[tallgirl]

There's a difference between wanting a disconnect, which is required, and wanting a specific kind of disconnect, such as the Big Red Switch.

It sounds like someone wants a Big Red Switch right at the meter.

 

[Sierrasparky]

to me it only makes sense to have a disconnect near the meter to shut off a backfeed.

 

[don_resqcapt19]

Our utility requires an outside disconnect near the meter for any solar or wind system that is utility interactive. They require this even where the serivce disconnect in inside the building.

 

[tallgirl]

to me it only makes sense to have a disconnect near the meter to shut off a backfeed.

From a fire safety standpoint, it makes sense to have a complete "Kill all electricity everywhere dead" set of disconnects, including one on the roof.

PV isn't like the PoCo.

 

[Jesse7623]

I think you misunderstood one detail. They want a way to ensure the PV output to the grid is off without pulling the meter, and/or without shutting down utility power to the property.[/QUOTE]

Interesting...hmm, No "They" refers to the FD when they show up and literally pull the meter.

 

[tallgirl]

I think you misunderstood one detail. They want a way to ensure the PV output to the grid is off without pulling the meter, and/or without shutting down utility power to the property.

Interesting...hmm, No "They" refers to the FD when they show up and literally pull the meter.[/QUOTE]

Nope, totally understood the requirement.

The issue is that not all inverters go one way. Some inverters are pass-thru with the line side lugs being bi-directional. In those instances, you have to have a way to kill not only the power to the grid, but also any load-side power.

Make sure you know what the inverters do =and= what's required.

 

[Sierrasparky]

From a fire safety standpoint, it makes sense to have a complete "Kill all electricity everywhere dead" set of disconnects, including one on the roof.

PV isn't like the PoCo.

Yes that also. I was not singling out disco at the meter panel.

 

[c_picard]

Interesting,

Where I've worked the utility requires visible-break, exterior, lockable AC disconnects, for a few reasons...
If you violate an interconnection agreement, they'll lock you off.
The visible break detail has to do with their safety regs.
Exterior, for obvious reasons, they retain the right to shut you down as a producer at any time for any reason,
go ahead, try to dispute that!

Most Fire Dept's that have been briefed on PV systems know that if you pull the meter, the AC side is dead. They also have been trained to not vent the roof through the modules.

 

[jaggedben]

Nope, totally understood the requirement. The issue is that not all inverters go one way. Some inverters are pass-thru with the line side lugs being bi-directional. In those instances, you have to have a way to kill not only the power to the grid, but also any load-side power.

I've seen a couple systems that were required to have a disconnect to kill load-side power from batteries and the like. I've seen many systems that were purely utility interactive, no pass-thru or the like, that were required to have an AC disconnect on the outside of the property. The OP appears to be asking about the latter situation.

 

[jaggedben]

Interesting...hmm, No "They" refers to the FD when they show up and literally pull the meter.

The OP was pretty clear that 'they' in this case was the utility.

 

[tallgirl]

The OP was pretty clear that 'they' in this case was the utility.

And "they" could still be fronting a requirement for the fire department.

Unless the PoCo wants to control when the inverters come on and start exporting power, UL 1741 says that the inverters DO NOT immediately begin to sell power once the power is restored.

The other possibility is that the PoCo is ignorant about UL 1741.

The only other possibility is that the PoCo is concerned about positive voltage gradient, and that would pretty much mean a commercial array, not some residence.