What the inspectors looked for

My DIY grid-tied PV system just passed City inspection last week, and Utility inspection a couple days later. However, it did NOT pass on the first try. Here are some observations for the benefit of forum readers. (This is for San Jose, California.) I'd also be interested in what, if anything, inspectors flagged for other readers.

HOSES NOT STRAPPED DOWN. I had one 3' length of flexible nonmetallic conduit just sticking out. Yup, I should have secured it. Interestingly, I was also supposed to secure the short lengths of the same thing, for instance, between the DC disconnect and the inverter. This was perhaps and 18" length of hose, and rigidly anchored at the fittings at each end. Ok, I put straps on those, too, maybe 6" away from the end points. This was enough to pass.

NO WARNING LABEL ON CIRCUIT BREAKER PANEL. I was told by the City that the Utility would require this, and pasted directly onto the outside of the circuit breaker panel. My plans were to put the "Directory of power generation sources" on a plaque 2 feet to the left of the breaker panel. I put on a label, and it passed City. When the Utility came by to inspect, their Meter Tech put on their own label warning of generator sources, which said about the same thing. Maybe the City inspector had seen the Utility stickers, and assumed they were provided by the installer. Whatever, it wouldn't hurt to put such a sticker on your installation. My text was something like, "Directory of power sources feeding this panel - 1. Photovoltaic System (disconnect switch to your left) 2. Regular PG&E Electric Service"

AC DISCONNECT WIRED WRONG WAY. The City inspector wanted to see the Inverter connected to the top (line) side of the switch, with the rationale that it was custom for the power to flow from top to bottom. However, I had wired it up the other way, with the mindset that when the switch is open, it is customary to think of the bottom (load) side terminals as being de-energized. I found support for my position later in a John Wiles article on the internet. As soon as the return inspector saw the name "John Wiles," he rescinded the complaint.

SOLAR MODULE INTERCONNECT CABLES NOT SECURED. On the roof, the inspector wanted to see the MC cables going from module to module tie-wrapped to the racks. I had walking space between separate sections of my array, and the cables were laying loose on the roof deck. I'm not sure of the reasoning behind securing the cables. The first inspector implied that it was so that someone wouldn't trip over the cables, which would suggest that the cables are best flat against the roof. The second inpsector thought it was to keep the cables from degrading on the hot roof surface, suggesting that it would be better to have the cables a few inches off the roof. I took up the slack and secured with large tie-wraps. It didn't take long. I chose to leave the inter-module portion of the cables lying flat on the roof, and it passed.

THWN INSTEAD OF THWN-2 USED FROM ARRAY TO DISCONNECT. The kit that I bought included some type TC wire, rated THWN/THHN. The inspector was unfamiliar with the wire, and had to check whether it was OK to put it in conduit (2 conductor TC cable looks like Romex, which is no good in conduit). The NEC said it was ok. But the inspector immediately flagged the THWN rating (this seems to be a shortcut check, THWN-2 would not have raised a flag, but for other ratings, they want to see the calculations). I showed my work, and we discovered that the wire was rated for 90 C at dry/damp, but only for 75 C at wet. And conduit is considered wet, because water tends to collect in it. When wet, the cable would have supported 11.7 amps with safety factors and deratings built in for hot sun. The short circuit current of my panels was about 14A. I discovered that if you go to Home Depot, Lowe's, etc., that you can't find #10 building wire in THWN-2 - it's always plain THWN. But #8 gauge wire always seems to be marked THWN-2. I don't know why this is, and it looks like the same insulation to me. Ironically, the thicker #8 wire was more flexible than the #10, because it came standard with 19 strands instead of 7. I pulled the new wire through the conduit, and had a 2' sample left over to show to the inspector.

As a note, the inspector said that all disconnect switches are supposed to be at least 3' from any natural gas vents, which could be a problem if your gas service come in at the same place as electrical. However, he said they often let it go if it's an outdoor, well-ventilated location.

Another observation is that the City inspectors had John Wiles's articles in their briefcases, and may have been working off a checklist developed by the same. Clearly, the man is highly revered in the Inspection community.

I FAXed the City sign-off to the Electric Utility (PG&E), and the next day, I got an email saying that a Meter Technician would come out to inspect the system and install a new meter. The day after that, we were surprised to see a new meter already installed, and the PG&E inspection tag. I suspect they don't check very much, and count on the City to enforce safety issues.

On the back of the inspection tag were some check boxes for common reasons for failure, something to keep in mind. They involved the AC disconnect not being within 10 feet of the meter, or not within sight, or not having access to the meter or disconnect.