Hello Matt, Both hands up here too. One in the factory and one in the field. I require technicians to use the UL 1703 standard dc test potential of 2 times maximum system voltage plus 1,000 volts (or 3,000 vdc). Be safe. Wear your gloves.
Joel Davidson ----- Original Message ----- From: Matt Lafferty To: 'RE-wrenches' Sent: Monday, April 27, 2009 8:08 PM Subject: Re: [RE-wrenches] To Megger or not to Megger Hi Keith, Both hands up here. From day 1 in PV. Every single field-installed current carrying conductor to the point of termination. AC & DC. BEFORE energizing them! One megger lead on the conductor, the other on the raceway or ground-wire. Megger @ 1kV. Must be greater than 250 Megohms to pass. Record the values on your commissioning sheet. I only meggered the actual arrays on projects where it was a requirement and I only did that following specific procedures provided by the module manufacturer. No procedure from the mfr = No array megger. I believe it's a critical thing to do as part of the commissioning. But then again, I don't like ground faults or fires. I'll never forget a couple of head scratchers that the megger found.... One was a perfectly fine, 6' long piece of Orange #12 XHHW-2 that would only pull 40 Megohms installed in EMT. Pulled it out and replaced it. Inspected it for any visible flaws. None found. Not a scratch or scuff. Used it as a training tool for my guys. Hung it on the wall over my desk as a handy reminder. If anybody wants a picture... The other was interesting, too. The very first PV system I ever installed. Was shooting the DC circuits from the inverter all the way to the connector on the output jumper cables at the modules. Megger showed dead short on one wire. Fluke 79 on ohms showed clear. Hit it with the megger again. Dead short. I'm known for being anal about conduit and wire installation, so this was quite unexpected, not to mention a little embarrassing. This happened to be a Solarex Millennia Integra system with an Omnion inverter and the array happened to be scattered all over this roof. For those of you who who have dealt with that situation, you'll understand what a cluster-*$#! that is... Especially being my very first PV system and all... I wasn't anywhere near confident that I had a clue by that point. All ready to see my first install fire up and this happens. It was my first install and I had 3 people getting paid prevailing wages to learn... I was learning too, but I wasn't making anywhere near prevailing wages, let me tell ya. Well, it was early January, late in the day and foggy as foggy gets, but we went back onto the roof anyway. Yeah... Overtime for everybody but me. We opened up the condulets and J-boxes for inspection. Pulled all the wires up out of the J-boxes. Pulled the endcaps and ground clips off (unique components of the Integra product). Couldn't find anything suspicious. Shot it with the megger again, and it was all clear. But no sign of anything that could have been shorted. We put everything back together and shot it again. Dead short! Aiyeeeee! Call it a day. Go home. I couldn't get back to that site until about the same time the next day. Foggy again. Only took 1 helper with me this time. We completely repeated the entire exercise, with exactly the same results. By now, I was pretty sure this solar stuff wasn't my calling. I've always been regarded as a gifted trouble-shooter and all I could say at this point was that I didn't know _____! All signs pointed to it being associated with one of the J-boxes or the endcaps or the ground clips, but there was NOT a thing we could see. Oh, well. I would have to come back another day. When I went back, I took the same helper and made sure I had all day if necessary to fix the problem. No matter what it turned out to be. We planned to take it apart 1 piece at a time and re-shoot it with the megger after each step. I left my helper on the ground with the megger while I took it apart on the roof, 1 screw at a time. Again. Well, lo and behold, he hollers up that "It's clear" when I pulled the cover off one of the 2-gang bell boxes. Hadn't moved a wire. Just took the cover off. Let me tell ya, I stuck my nose and four eyes in that box real close, but didn't touch any wires. The box was a tight fit with those big, sealant-filled blue wire nuts that came with the Solarex Kit, but I still couldn't see anything wierd. "Shoot it again." "All clear, boss." I put the cover back on and installed all the screws. "Shoot it again." "Dead short." We had a talk later about shouting things like "Dead short" on the jobsite, but I won't get into all that right now. I took out one of the cover screws. "Shoot it again." Same answer from the ground. I took out a second screw. "Shoot it again." This time the reply was different. I took out the third screw and we repeated the process. Still clear. And the fourth. Still clear. WTF? I lifted the cover for what seemed like the hundredth time. I studied the nested wires, all neatly and systematically put into what I had thought would be their final resting place... Days before and time and time again at this point. I began gently lifting the wires out so they all stood up like dandelions in a spring lawn. I inspected them for the nth time. Looking for a stray strand outside its protective hat. Nope. Overtightened wire nut with the spring or a conductor coming out the tip? Nope. But what's this little, nearly imperceptible dent in the side of this wire nut? As I looked closer, I could see that it was round, flat bottomed and about the same diameter as a 6-32 screw. Hmmmm. I rolled the wires back into their resting position. Uh, huh. This particular wire nut's natural home was directly under the cover screw which had cleared the fault when removed and the dent lined up perfectly. The screw could just barely be long enough to pierce the plastic and contact the wire-spring. I replaced the wire nut, repositioned the conductors to make sure we wouldn't have a repeat, and buttoned up the J-box. I put the wirenut in my pocket for later reference. One more megger shot proved the system to be all clear. We could now energize the DC and do our Voc & Isc testing prior to startup. Thank goodness the sun was shining. I wasn't happy about this whole ordeal, but it was a good thing we caught it with the megger before we put the power to it. That wire nut became the first exhibit in what became my collection of training materials for the "what can go wrong and why we do these procedures" trainings. Verification that cover and mounting screws cannot come in contact with energized equipment was officially put in the checklist. All cover & mounting screws in all types of enclosures. There would be no exceptions. There would be no excuses. I actually had to write one guy up for a violation of this at one point. Good thing we caught that one with the megger before putting the power to it. I would posit that at least one of the recent PV fires would absolutely have been prevented if the installer followed the procedure described above. Too bad most don't. Kudos to those of you who do. It's only a matter of time until more and more of these AVOIDABLE problems surface. If you don't have a megger, get one. If you have one, use it! The Fluke 1520 is a nice unit. I recommend it over analog models. I cut my teeth with analog gear, but really like my 1520. A lot! Rugged instrument that gives you an actual number to write on your commissioning sheet. In addition to Megohms, it also does VAC, Lo Ohms, Continuity, has a display backlight, Lock and Zero functions and my favorite.... Battery Check! Reads out an actual % value for your battery condition. Nice! Uses 4 "C" cells. I hope more hands go up on this topic. Thanks for asking, Keith. Peace and Palm Trees everybody, Matt Lafferty ------------------------------------------------------------------------------ From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Keith Cronin Sent: Monday, April 27, 2009 2:37 PM To: RE-Wrenches Subject: [RE-wrenches] To Megger or not to Megger Hi I was wondering, by a show of hands, how many of you megger every project? Do you have a cut off- like if it is "x" sized system, you will or decide to opt out of performing this task? ------------------------------------------------------------------------------ _______________________________________________ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Options & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules & etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
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