I have a solar farm and a problem, I think. I will be brief and to the point:

1. The solar farm service equipment has an 800 amp disconnect. The voltage is 480v. There is no overcurrent protection at the service equipment in this location (in the middle of an open field).

2. The wiring travels underground approximately 600 feet, and before entering a school it enters an 800 amp FUSED disconnect.

3. The installation is a line-side tap into the power company service on the school. So the solar farm is of itself, a new service.

My concern is that the wiring from the farm service (located in the middle of the field) travels 600 feet underground without overcurrent protection. It is installed in schedule 80 PVC conduit buried at least 18 inches deep...but still. If the fuses blow at the other end, this wiring is still ON. Right? But I would think that this outside feeder it is required to have overcurrent protection...I am studying the code right now on this one. If anyone can point me in the right direction....

THANKS

*cricket*

Is there any way to prevent this or am I stuck with what may be an outside feeder tap of unlimited length?

What you describe is NOT a feeder tap (by definition), so 240.21(B)(5) wouldn't apply. And, a solar PV system is NOT a service (by definition) so Article 230 wouldn't apply either.

Overcurrent protection of the PV supplied conductors for this system must meet 705.30(A) / 690.9 of the NEC which both reference Article 240.

240.21 states that overcurrent protection must be provided at the point where the conductors receive their supply.

I believe what you describe is a violation of the code.

Thanks Bryan. Are you saying that I need to view the solar farm as "a load?"

Additionally, 690 trumps 705 (the fact that it references it specifically) and 690.9 is giving them an out (see exceptions).

What can I do, if anything, to require the OPD?

I think you should strongly recommend overcurrent protection but I am not sure you can make them do it if they are willing to go to the wall about it. I really do not see a hazard to life or structures if these conductors burn to a puddle of molten copper underground but it will be expensive to fix.
Sometimes a little common sense will prevail where the government hammer fails.

The 600 feet of unfused conductor travel through a county landfill. Now, do you see a potential problem here?

From what I understand about PV systems (and that questionable) they are considered self limiting - that the output is limited by the production potential of the panels and so long as the conductors are rated for the maximum output, no overcurrent device is required until you interconnect to the power company (a much higher potential current). In other words, the conductors are rated for the maximum fault so you cannot have an overcurrent in the conductors. What worries me is a fault to earth... there is nothing to stop the flow. But 690 talks about ground fault protection being required for AC and DC systems, so it may be built in. Best check the manufacturer;s specs.
I am more familiar with AC systems where the inverter is at each panel and shuts down at any interruption of the house voltage - thus under ground fault the main at the building would ocpen, breaking the sensed voltage form the utility and this would shut down all the individual inverters.

Not particularly. Are you calling it a classified location?

no.

I may be confused, but it seems to me that once the PV - DC supply is converted to AC and hits the first means of disconnect, it now beomes normal premises wiring and thus meet general rules of conductor overcurrent protection.

I guess I am having a hard time to understanding the installtion as described.

I'm sure that I'm confused. If possible, I will post a pdf of the one-line diagram, or at least some of it. It may take me a day or so.

Well the cells are dc and there is a current limit on the cells.
So if the limit of the cells is say 100amps, that is all they provide. Period.
Kinda like a generator rating. If you have say a 500kva generator. Then above that rating if the load calls for it . pretty much the generator will stall or reduce its voltage because it can't keep up with the load.

My 2 cents.

Am I to late to give my 2 cents worth?

Nick, I have a couple of questions.
Is this an Utility interactive system?
Are there overcurrent protection devices in the "collector box or boxes" on the AC side of the inverters?

I agree with Byran a PV system does not fall under the NEC definition of service, so what do we call them??

Some PV contractors tell me that the are appliances what say you guys on that point?

I was taught that when dealing with PV systems you have to think backwards.

So if indeed this is an utility interactive system, as soon as the utility power is taken away (been told within 6/10 of one cycle) the inverters stop the AC output.

The overcurrent proctection devices located in the collector box or boxes will "limit" the current that can be placed on the 600 foot "feeder" conductors.

If there is a ground fault or short circuit in the "feeder" the fuses in the 800 amp disconnect will open (this is where the backward thinking comes in) and the inverters will stop producing AC power.

The PV panels would still be producing DC power and the DC side of the inverters will still be energized, but no danger would be present.

IMHO
Neal Burdick
City of Tampa
Construction Inspector II

Never too late, Neal.



To the best of my knowledge - yes it is.



I'm not sure. Will have to check into that.



A big pain in my butt? (just kidding) I'm pressed for time lately. I have been meaning to post a sketch and will try to do so this week...

Thanks!