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Posted By: NJWVUGrad PV Disconnect and 6 Disconnect Rule - 04/17/11 07:06 PM
This seems to be a murky area between engineers, AHJ's, contractors and utilities and I am curious to anyones input.

Does a Supply side connection of a PV system , as allowed on 690.64, and its associated PV AC Disconnect count toward the 6 disconnect rule?

The scenario that I am curious about is a typical Northern NJ Multi- Tenant building where PSEG has 6 CT cabinets (metered) feeding (6) 400-600A disconnects that then feed meter banks for individual tenants. Typically one of these metered services is the House service (common area lighting, site lighting, etc) and the one that the PV array would be feeding. The supply side connection is made after the meter and before the main.

Any experiences?
Posted By: Obsaleet Re: PV Disconnect and 6 Disconnect Rule - 04/17/11 07:24 PM
I say it counts for the simple reason, that if you such 6 switches off the power then should be off to all loads.

Posted By: NJWVUGrad Re: PV Disconnect and 6 Disconnect Rule - 04/17/11 08:24 PM
Ok, now what about when the PV array is tapped on the supply side of the main disconnect, shutting the main disconnect would de-energize all downstream loads from both sources (utility & PV)?
Posted By: Obsaleet Re: PV Disconnect and 6 Disconnect Rule - 04/18/11 03:08 AM
Yes again. No need to back feed the POCO lines. Think of a generator. Or servicing the meter base or overhead drop.
Posted By: sabrown Re: PV Disconnect and 6 Disconnect Rule - 04/18/11 04:58 PM
I see your point. The DC from the solar array enters an inverter after a disconnect. The inverter is "Grid tied" and can not generate power once main power to the building is removed. Does the solar array disconnect count as one of the 6?

The answer is, it depends. If the solar DC power never enters the buillding, I would say no. But, To inform the fire department of possible hazards required 230.2(E). If the DC enters the building, well, under 230.2 "Different Characteristics" applies and allows the additional disconnects with Identification. Disclaimer: Local jurisdictions may have rules for this, so as always talk to your local AHJ.

Posted By: Tesla Re: PV Disconnect and 6 Disconnect Rule - 04/19/11 04:33 AM
The trick inverter boxes absolutely will not permit power to flow in the event of grid disconnection no matter how it happens.

Next, due to the saturation effects in PV solid state physics they are NOT to be considered an 'infinite bus.' It's the infinite bus character of line power that dictates the performance of OCPD. ( Breakers & fuses )

Having said that, for anything this new, get an opinion from the local AHJ and Poco. Why take a chance they've got an alternate insistence?
Posted By: NJWVUGrad Re: PV Disconnect and 6 Disconnect Rule - 04/19/11 01:23 PM
I agree to always check with the AHJ & POCO, in this case we are trying to come up with a design standard for a client constructing arrays on buildings all over the state. SO we are trying to come up with a default position on the issue, that could then be altered on a case by case basis.

Since we are on PV systems, what about the feeder that runs from a service panel to the PV sub panel. You have a panel on the PV side where a couple of 2 pole 20 amp and 30 amp breakers are, then it runs to the service panel. At this point the current is flowing toward the service panel. On the service side, you tap the main service conductors.

Now if the PV system is shut down for any reason, the current will still be on the feeder from service panel to PV sub panel.

Shouldn't there be some sort of disconnecting means and some sort of over current protection on that feeder as it leaves the service panel?

You have unprotected wires running from the service panel to the PV system, is that safe?
Posted By: NJWVUGrad Re: PV Disconnect and 6 Disconnect Rule - 04/19/11 01:49 PM
I agree harold, I have noticed (to the annoyance of many design engineers) that more savvy inspectors are applying the 10' tap rule for instances such as you just described.

Posted By: Tesla Re: PV Disconnect and 6 Disconnect Rule - 04/19/11 10:05 PM

My understanding is that should the grid go down so too does the inverter.

So there is no energy on the feeder.

The DC current going to the inverter backs up and saturates -- and stops flowing.

The electronics inside the trick inverter can tell when the grid is out.

This is a specific design feature demanded by our Pocos out here to get the tax credits and the utility ( by state provision ) rebates.

As for the feeder going the other way -- like night time -- ours are sized such as to qualify easily under the 25-foot tap rule. Still they are always placed as close as possible to the Service for reasons of economy.

So it's a total non-problem where I sit.

The one thing I've noted is that the PV boys want cheap labor -- that is new to the electrical trade -- so the result is that many, many installs are raceway ugly. Too much Sealtite where a clean EMT run would do nicely.

Posted By: HotLine1 Re: PV Disconnect and 6 Disconnect Rule - 04/20/11 01:30 AM
I would say about 75-80% of the resi solar installs are grid tied via a backfed CB, as opposed to line side taps on the service feeders. As Tesla said, the inverters shut down output when there is a POCO disruption, and the required utility exterior AC disconnect is in place.

As to the disco being a possible '#7'....SABrown has that covered.

John and Tesla,

I understand that when there is "No light" the inverters will shut down. However IF you tap the main service entrance conductors. There will always be current/voltage on the feeder between the last connection of the PV system and the service entrance. Right?

Even if the feeder that runs from service panel to PV system, there will still power on the feeder but this will be protected by the CB in the service.
Posted By: HotLine1 Re: PV Disconnect and 6 Disconnect Rule - 04/20/11 02:36 PM

The 'tap' being ahead of the main OCP will have power unless there is a POCO interuption. That goes for the panel, and the utility side of the inverter.

Most, if not all of the inverters will shut OFF when the circuitry senses 'no power' from the POCO grid tie, like a power failure, or pulling the meter IF the line tap is ahead of the main OCP.

You can achieve the inverter shut down by opening the POCO required disconnect (AC).

Posted By: renosteinke Re: PV Disconnect and 6 Disconnect Rule - 04/20/11 03:52 PM
The NEC, like all codes, can only react. Technology will ALWAYS be ahead of our rulebooks. Why do you think I keep advocating for good design, rather than 'code complaince?'

It seems obvious: everything should have an 'off' switch. With solar panels, IMO this switch needs to be as close to the source of the power as possible. If your only disconnect is at the panel, a fault in the supply line will never be shut off - at least, as long as the sun shines.

Getting back to our 'six throws' rule: I don't want to have to flip more than six switches to kill power to every branch circuit in the building. Whether that means I flip six branch circuit breakers, six supply disconnects, or some combination of the two doesn't matter: I want no more than six switches.

Can we count on the inverter as a disconnect, simply because it disconnects the solar feed in the absence of utility power? IMO, no. Make that "Hell No." Microchips and relays fail, or 'leak.' I want a real switch.

Since I want my six disconnects grouped together, I guess that means I want a disconnect on both ends of the solar feeder. Redundant? I don't see it as such. Rather, I see them as serving different purposes. One is there to contain a fault, while the other is there to remove the supply.
John and Reno,

Beside the six switch rule. My first concern is, if you tap the service entrance conductors and run to PV equipment. Do you need a disconnect or over current protection once it leaves the service panel?

What happens if someone cuts that wire or pipe? If it is dark and the POCO has a black out the answer would be nothing.

If the POCO blacks out during the day, the inverter will turn off. All is safe.

BUT if the PV goes down and the Poco is on, then that wire/pipe is energized.
Posted By: Vindiceptor Re: PV Disconnect and 6 Disconnect Rule - 04/20/11 05:56 PM

I have successfully installed PV disconnects in addition to the six existing 'utility' service disconnects twice. In one case our PV disconnect was the seventh disconnect and in another we had two 800A PV disconnects in addition to the six 'utility' disconnects. Each service 'source' is allowed to have six disconnects according to the code, utility, wind, solar, cogen, etc. I would recommend confirming that your AHJ is up to date on this allowance AND will allow it before proceeding though as many have their own requirements and/or interpretation of 230.2(A), 230.71(A) and 230.82. 230.71(A) being the most critical because it allows up to six disconnects PER service and 230.2 defines the utility and PV as two separate services which would therefore allow up to 12 disconnects.

You can not rely on the inverters required anti-islanding features to shut down the PV service supply when it is tapped on the line side of the utility disconnects as most all commercial systems should be.

Most of the PV disconnects we install are in the 600A to 2000A range and are subject to the 10-25 foot tap rules, BUT some AHJ's and inspectors have asked why we're installing the disconnects so close to the utility service since we had inverter disconnects 200-800 feet away, they are actually considering the feeder a utility lateral and as such do not see a need for the additional fusible disconnect since the utility is not required to do it. We install them regardless of that though as the fire department is usually more interested in having the disconnects as close together as possible.

Even AHJ's that want the PV disconnects within 10-25 feet have allowed us some leeway when there was NO way to get a 1600A-2000A visible blade fusible bolt switch that close, as close as possible was still acceptable even if 50-75 feet was the best we could do. We have not done this, but they have been free with expressing their allowance of this.
Posted By: renosteinke Re: PV Disconnect and 6 Disconnect Rule - 04/20/11 06:14 PM
I cannot agree that the code would allow you to, say, have twelve branch circuit disconnects as the onlt means of disconnecting the building simply because there are two "services."

As far as I'm concerned, there's only one 'service' when there's only one distribution system within the building - np matter how many sources of supply there might be to that system. I will concede that the code language is conflicting on this point.

The conflict is seen in the wording of the section that discussed the number of means of disconnection. It is clear that the authors imagined separate systems - for example, where a 480/277 service served 3-phase loads and a 120/240 service served single-phase loads. I cannot accept that the authors ever imagined both services feeding the same panel.

A similar situation might be where a generator is used- except that the traditional transfer switch was designed to ensure that only one of the sources was ever used at one time.
Posted By: renosteinke Re: PV Disconnect and 6 Disconnect Rule - 04/20/11 06:20 PM
Harold, I cannot speak for NEC requirements. I don't think the code panel itself has come to grips with the various design issues- and the solution to that gets into the basic arrangement of the NEC. Personally, I think ALL sources of power need to be grouped into their own section, and treated as a whole.

As for overcurrent protection, I see that as a design issue. That is, there ought to be overcurrent protection at the point of generation.

Where the two systems come together, there needs to be some way to limit power from 'going the wrong way.' This might very well mean a breaker at that point as well. Otherwise, you have the potential of a fault tripping the feed from one direction - but still have the risk of a backfeed to the fault.

I note that the UL-listed arrays with 'micro-inverters' at the array and a simple circuit to the panel require that you backfeed the power through a breaker into the panel.
Posted By: renosteinke Re: PV Disconnect and 6 Disconnect Rule - 04/20/11 08:17 PM
Vindeceptor ... you really got me thinking about this over lunch ....

Let's agree with your interpretation. That would mean that I could instal seven of the micro-inverter panels, backfeeding into six breakers in the panel- and not have any requirement to add a main disconnect, even if the 42-circuit panel was now full. (7 x 6 = 42).

After all, each of the micro-inverter units would be an independent service. Yet, none of the branch circuits would be powered only by a specific unit.

Add to that the main breaker, or the back-fed breaker on the Utility side, and you now need to flip EIGHT breakers to ensure that all of the branch circuits are dead.

I have a problem with this scenario. I can't speak for others - but I intend to have the next code cycle address this topic.
Posted By: HotLine1 Re: PV Disconnect and 6 Disconnect Rule - 04/20/11 10:49 PM
I would have to take issue with the above scenario. I don't know what to base it on real quick, but that sounds like an issue to me also.

Posted By: Vindiceptor Re: PV Disconnect and 6 Disconnect Rule - 04/20/11 10:57 PM

It's not my interpretation, others are doing this as well. The code is fairly clear on the allowance, I think the only issue is what the local AHJ or Fire Marshal has to say about it. The two that we have done were done out of necessity as the cost of upgrading the service equipment would have taken the project beyond the financially feasible point. Usually the appropriate signage and even embellishments on that (detail maps of disconnect locations) will more than satisfy the AHJ and Fire Marshal.

Are you referring to AC modules with integral inverters or small single phase inverters?

In your scenario where are your PV AC disconnects? I know of no utility that would accept a breaker as an AC PV disconnect. The PV disconnects have to have visible blades, either through the use of a window or in the case of smaller disconnects they must be openable when off for visual verification of the circuit being broken.

In the situation you're referring to the utility disconnect (or up to six of them) would be the sole premises disconnect since opening it will shut down the PV inverters. If that wasn't acceptable to the AHJ then a separate PV panel to gather all of the micro-inverter circuits and a panel disconnect would be acceptable I'm sure.

I personally haven't done anything smaller than 50kW with most systems being 500kW to 1MW so micro-anything isn't even a consideration.

Connecting 1MW into a 4000A service with six existing 800A disconnects with no main and only 36" of clear wall space on the other side of the room can be a challenge.

Posted By: sparkyinak Re: PV Disconnect and 6 Disconnect Rule - 04/24/11 12:36 AM
The six throws of the hand rules is per service. IMO, hybrid systems are a combination of multiple services in which typically only one is providing power to a building at one time. I agree its an ahj question however despite a few of my systems with multiple power sources, the main power supply can be disconnected with the throw of only one or two handles.

For example, my last AE system had 7 strings of panels. Although they combine to a single breaker, I would not count that as one of the six throws because my inverter does not run off the panels. They run off from the battery bank and still puts out 120/240. With grid ties, that's is a little different. It's a case by case basis. The inverter dc input breaker or the inverter AC out breaker would count only as one throw to the whole system providing no other system could power the system like a back up generator
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