Just went to check the Fluke 1520 price. Looks like it is discontinued. They do have a couple suggested replacements.
Just for reference, Bob On Mon, Apr 27, 2009 at 11:08 PM, Matt Lafferty <gilliga...@gmail.com>wrote: > 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 > > >
_______________________________________________ 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
