<div dir="ltr">Sam,<div><br></div><div>I'll try and answer your question as best I can. </div><div><br></div><div>AC or DC shouldn't matter when conducting insulation resistance testing (IRT) because the conductors shouldn't be connected to an AC or DC power source. You definitely can't conduct insulation resistance testing when the conductor is connected to any type of power electronics (inverter, MLPE, or RSD) because the high voltage can damage the electronics. The best practice is to run the IRT after the conductor has been run but before the ends have been terminated. </div><div><br></div><div>I understand you can insulation resistance test a string of modules with the module manufacturer's approval. </div><div><br></div><div>I'm partial to Fluke tools and have a 1503 IRT that's worked well for me. They have a site specifically dedicated to <a href="https://www.fluke.com/en-us/products/electrical-testing/best-solar-energy-industry-tools">solar tools</a>, and it looks like they recommend the 1587 FC. They're also coming out with a multi-function tool that will do IV Curve testing, IRT, and a few other measurements. It's not out yet, but it should be shortly.</div><div><br></div><div>Thanks,</div><div>Will</div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Tue, Oct 11, 2022 at 11:01 AM Sam Haraldson via RE-wrenches <<a href="mailto:re-wrenches@lists.re-wrenches.org">re-wrenches@lists.re-wrenches.org</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr">Wrenches,<div><br></div><div>In order to step up our commissioning and testing game and to take proactive steps to spot isolation faults and test insulation resistance prior to our systems getting PTO it is time to invest in a Megger. I am looking for your recommendations for being able to test both AC (single and three phase) and DC (600 to 1000 Vdc) conductors in a wide range of sizes typical to both residential and commercial systems. Ideally the equipment has the option to test to either bare copper or use MC4 leads. </div><div><br></div><div>Am I foolish to look for a single unit that tests both AC and DC or should I focus on two pieces of equipment? What is your experience with insulation resistance testing through RSDs, MLPEs, and modules? Are there brands that specifically state this is a no-go? Are there testers that can assist in providing a percentage from + or - to help point out the trouble spot or am I only going to find string-level detail? </div><div><br></div><div>Any recommendations </div><div><br clear="all"><div><div dir="ltr"><div dir="ltr"><div><div dir="ltr"><table border="0" cellpadding="0" cellspacing="0" style="font-family:"Trebuchet MS",Helvetica,sans-serif;line-height:16px;color:rgb(102,102,102);font-size:14px;border-spacing:0px"><tbody><tr><td width="0"></td><td><table border="0" cellpadding="0" cellspacing="0" style="font-family:"Trebuchet MS",Helvetica,sans-serif;font-size:1px;line-height:2px;border-collapse:collapse;border-spacing:0px;margin:0px;padding:0px"><tbody><tr><td style="font-size:13px;line-height:13px;height:13px;padding:0px;display:block"><div style="line-height:13px;height:13px;margin:0px;padding:0px"></div></td></tr><tr><td><table cellpadding="0" cellspacing="0" border="0" width="100%" style="font-family:"Trebuchet MS",Helvetica,sans-serif;line-height:2px;border-collapse:collapse;border-spacing:0px;margin:0px;padding:0px;width:383px"><tbody><tr><td valign="bottom"><table border="0" cellpadding="0" cellspacing="0" style="font-family:"Trebuchet MS",Helvetica,sans-serif;line-height:2px;border-collapse:collapse;border-spacing:0px;margin:0px;padding:0px"><tbody><tr><td><table border="0" cellpadding="0" cellspacing="0" style="font-size:12px;font-family:"Trebuchet MS",Helvetica,sans-serif;line-height:16px;border-spacing:0px"><tbody><tr><td valign="bottom" height="19" style="font-size:15px;line-height:19px;color:rgb(89,158,204);white-space:nowrap;font-weight:bold"><font style="font-family:"Trebuchet MS",Helvetica,sans-serif"><a href="mailto:sam@onsiteenergyinc.com" style="color:rgb(89,158,204)" target="_blank">Sam Haraldson</a></font></td><td valign="top" style="font-size:13px;line-height:13px;height:13px;padding:0px;display:block"><div style="line-height:13px;height:13px;margin:0px;padding:0px"></div></td></tr></tbody></table></td></tr><tr><td><table border="0" cellpadding="0" cellspacing="0" style="font-size:12px;line-height:16px;font-family:"Trebuchet MS",Helvetica,sans-serif;border-spacing:0px"><tbody><tr><td valign="bottom" style="line-height:16px;white-space:nowrap"><font face="Trebuchet MS, Helvetica, sans-serif">Installation & Service Manager</font></td><td width="6" style="line-height:1px;font-size:1px"></td><td width="6" style="line-height:1px;font-size:1px"></td><td style="font-size:13px;line-height:13px;height:13px;padding:0px;display:block"><div style="line-height:13px;height:13px;margin:0px;padding:0px"></div></td></tr></tbody></table></td></tr></tbody></table></td><td width="15" style="white-space:nowrap;width:15px"></td><td width="" valign="middle"><a href="http://www.onsiteenergyinc.com/" style="border:none;display:block" target="_blank"><img width="192" height="37" alt="" src="https://esr-storage.s3.amazonaws.com/images/21230/108433/default/images/218965d24e62dbfc42.jpeg?override=1564075269" style="border: none; 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