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</o:shapelayout></xml><![endif]--></head><body lang=EN-US link=blue vlink=purple><div class=WordSection1><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Meggerers,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Although shorting the terminals to perform the megger tests may provide the most uniform voltage profile, it is difficult to perform on many arrays and adds unnecessary complexity to a test that needs to become routine for all PV installations.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>The appropriate way to perform the test at the combiner box level for negatively grounded systems is as follows (voltage would be applied backwards for a positively grounded array):<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoListParagraph style='text-indent:-.25in;mso-list:l3 level1 lfo4'><![if !supportLists]><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><span style='mso-list:Ignore'>1.<span style='font:7.0pt "Times New Roman"'> </span></span></span><![endif]><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Open all fuse holders and make sure no fuses are mounted in the holders.<o:p></o:p></span></p><p class=MsoListParagraph style='text-indent:-.25in;mso-list:l3 level1 lfo4'><![if !supportLists]><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><span style='mso-list:Ignore'>2.<span style='font:7.0pt "Times New Roman"'> </span></span></span><![endif]><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Remove any connected surge arrestors from the circuits as these will conduct during the test and may fail.<o:p></o:p></span></p><p class=MsoListParagraph style='text-indent:-.25in;mso-list:l3 level1 lfo4'><![if !supportLists]><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><span style='mso-list:Ignore'>3.<span style='font:7.0pt "Times New Roman"'> </span></span></span><![endif]><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Remove the grounded feeder conductor so there is no connection to the inverter.<o:p></o:p></span></p><p class=MsoListParagraph style='text-indent:-.25in;mso-list:l3 level1 lfo4'><![if !supportLists]><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><span style='mso-list:Ignore'>4.<span style='font:7.0pt "Times New Roman"'> </span></span></span><![endif]><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Connect the negative of the Insulation Tester to the grounding connection in the combiner box. <o:p></o:p></span></p><p class=MsoListParagraph style='text-indent:-.25in;mso-list:l3 level1 lfo4'><![if !supportLists]><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><span style='mso-list:Ignore'>5.<span style='font:7.0pt "Times New Roman"'> </span></span></span><![endif]><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Connect the positive of the Insulation Tester to the negative connection in the combiner box.<o:p></o:p></span></p><p class=MsoListParagraph style='text-indent:-.25in;mso-list:l3 level1 lfo4'><![if !supportLists]><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><span style='mso-list:Ignore'>6.<span style='font:7.0pt "Times New Roman"'> </span></span></span><![endif]><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Apply either 500V or 1000V to the negative connection and wait for the insulation resistance to achieve at least 100kOhms.<o:p></o:p></span></p><p class=MsoListParagraph><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Insulation resistance will vary based upon module construction, moisture on the modules and conduit systems, and cycle of the moon (oh wait, that’s the PMS procedure—sorry)—actually irradiance and temperature can make a difference. By adding 500V or 1000V to the negative side of the strings, the positive side is going to go to 1000V or 1500V. This does not violate the listing of the product as this is a temporary test. These types of tests are customary for 600Vac wiring systems and they should be mandatory in PV systems of any size operating above 100V. If the module is damaged by this test, it was a faulty module since all module internal wiring is required to withstand 2200V to ground throughout the unit—diodes and all. By testing in the normal voltage bias that the product sees during operation, it will more thoroughly stress the higher voltage parts of the array which are more critical for the long-term reliability of the PV system.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>If a resistance of 100kOhms cannot be achieved, take all the grounded-side string conductors loose from the combiner block and test each one individually to see if there are variations in resistance. If no variations exist, the modules might be a more leaky variety and a new, lower threshold would need to be established with the help of the module manufacturer.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Happy testing and don’t forget to use your gloves.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Bill.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in'><p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'> re-wrenches-bounces@lists.re-wrenches.org [mailto:re-wrenches-bounces@lists.re-wrenches.org] <b>On Behalf Of </b>Bill Hoffer<br><b>Sent:</b> Wednesday, November 17, 2010 4:36 PM<br><b>To:</b> RE-wrenches<br><b>Subject:</b> Re: [RE-wrenches] Megger for array testing<o:p></o:p></span></p></div><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Joel <br><br>You are correct about the UL testing requiring 2 x system voltage plus 1000 volts. The UL requirement is also to ramp up to the full voltage in 5 sec and held for 1 min, which I believe most meggers are capable of. The test is considered a failure if greater than 50 uA current is measured. The difference is that the connection is between the shorted outputs of the module and the ground. In the case of the required factory tests one end of the high pot testing device is connected to the frame (ground) and one point is connected to both the negative and positive module terminals shorted together. In the UL test it is done with the module submerged one terminal of the high pot tester is connnected to a ground plane in the water and the other terminal is connected to the negative and positive terminals shorted together. In both cases the voltage potential across the module terminals (through the module) is 0, but between the terminals and ground is the 2 x system voltage plus 1000. The module never sees 2200 volts potential across the cells and diodes. The test is normally run again reversing the polarity, but the terminals still are shorted together. I have performed this test in the factory and observed it being done this way during UL testing. <br><b><br>UL1703 Section 21 Leakage Current Test </b>specifies shorted module output circuits System Voltage is the test level required<br><br>21.5 All accessible parts and surfaces are to be tested for leakage current. <b>The positive and negative<br>terminals of an unilluminated module are to be connected together and to one terminal of a dc power<br>supply.</b> Both polarities of the source connection are to be used, unless it can be shown that one polarity<br>will represent both. Leakage currents are to be measured between the part or surface and the other<br>terminal of the power supply. System Voltage is the test level required and <br><br><b><span style='font-size:10.0pt;font-family:"Arial","sans-serif"'>UL1703 Section 26 Dielectric Voltage-Withstand Test </span></b><span style='font-size:10.0pt;font-family:"Arial","sans-serif"'>does not specify shorted module outputs, but does specify 2 x system voltage plus 1000V<br><br><b>UL1703 27 Wet Insulation Test</b></span> does specify Shorted output terminals of the module (and only 500vdc)<br>27.3 After two min of immersion in the solution, the <b>insulation resistance between the shorted output<br>terminals of the module or panel and the solution is to be measured, in both polarities</b>, with an instrument<br>having a voltage of 500 Vdc.<br><br><b>43 Factory Dielectric Voltage-Withstand Test</b> Also doe snot specify shorted out puts<br><br>The IEC 61215 is more explicit in all test cases it specifies using the shorted output terminals for all these tests. IMHO the IEC is the better document to follow (which is what the listing agencies all do when things are not defined well in UL1703). The industry will be much better off once we standardize with the IEC!<br><br>In my experience all three tests for UL listing are performed in the same way on shorted output terminals. I would recommend that the megger test be performed in the same way especially for field confirmation procedures for commissioning a system. This will still give you the intended results (identifying a potential short to ground) without the risk of applying unnecessary voltage across the module cells or diodes. I do not want to be explaining a failed module to the manufacturer or customer after subjecting it to 2200 + volts across the cells or diodes! You would never meg across an inverter input either, even though they are also high pot tested for listing. Of course standard procedures for megging wire runs without the inverter or modules in the circuit can be done at those higher levels without a problem.<br><br>Bill<br><br>Bill Hoffer PE<o:p></o:p></p><div><p class=MsoNormal>Sunergy Engineering Services PLLC<br>2504 Columbia Ave NW<br>East Wenatchee WA 98802-3941<br><a href="mailto:SunEngSer@gmail.com" target="_blank">SunEngSer@gmail.com</a> (509)470-7762<br>Cell(509)679-6165<br><br><br>On Wed, Nov 17, 2010 at 9:05 AM, Joel Davidson <<a href="mailto:joel.davidson@sbcglobal.net">joel.davidson@sbcglobal.net</a>> wrote:<o:p></o:p></p><div><div><p class=MsoNormal><span style='font-size:10.0pt;font-family:"Arial","sans-serif"'>Hello Drake,</span><o:p></o:p></p></div><div><p class=MsoNormal> <o:p></o:p></p></div><div><p class=MsoNormal><span style='font-size:10.0pt;font-family:"Arial","sans-serif"'>I think you should talk to a Sanyo Solar engineer to get accurate information. Every Sanyo and other brand UL listed modules must be dielectric voltage-withstand factory tested to 2 times system voltage plus 1,000 volts. I hi-pot test modules in the factory at 3,000 volts so they will meet UL and also IEC standards. I megger field test arrays at 1,000 volts to find module, connector, and wiring problems. Megging at 500 volts is ok, but it may not reveal wire insulation problems.</span><o:p></o:p></p></div><div><p class=MsoNormal> <o:p></o:p></p></div><div><p class=MsoNormal><span style='font-size:10.0pt;font-family:"Arial","sans-serif";color:#888888'>Joel Davidson</span><span style='color:#888888'><o:p></o:p></span></p></div><div><p class=MsoNormal><span style='color:#888888'> <o:p></o:p></span></p></div><blockquote style='border:none;border-left:solid black 1.5pt;padding:0in 0in 0in 3.0pt;margin-left:3.0pt;margin-top:5.0pt;margin-right:0in;margin-bottom:5.0pt'><div><div><div><p class=MsoNormal><span style='font-size:10.0pt;font-family:"Arial","sans-serif"'>----- Original Message ----- <o:p></o:p></span></p></div><div><p class=MsoNormal style='background:#E4E4E4'><b><span style='font-size:10.0pt;font-family:"Arial","sans-serif"'>From:</span></b><span style='font-size:10.0pt;font-family:"Arial","sans-serif"'> <a href="mailto:drake.chamberlin@redwoodalliance.org" target="_blank" title="drake.chamberlin@redwoodalliance.org">Drake</a> <o:p></o:p></span></p></div><div><p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Arial","sans-serif"'>To:</span></b><span style='font-size:10.0pt;font-family:"Arial","sans-serif"'> <a href="mailto:re-wrenches@lists.re-wrenches.org" target="_blank" title="re-wrenches@lists.re-wrenches.org">RE-wrenches</a> <o:p></o:p></span></p></div><div><p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Arial","sans-serif"'>Sent:</span></b><span style='font-size:10.0pt;font-family:"Arial","sans-serif"'> Wednesday, November 17, 2010 7:36 AM<o:p></o:p></span></p></div><div><p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Arial","sans-serif"'>Subject:</span></b><span style='font-size:10.0pt;font-family:"Arial","sans-serif"'> [RE-wrenches] Megger for array testing<o:p></o:p></span></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><p class=MsoNormal>Hello Wrenches,<br><br>Looking through the archives on using a Megger for testing modules, it appears that it is best to keep voltages to 500VDC. I read all that I could find. <br><br>Talking to a Sanyo representative, I was told that keeping test voltage under 600 would not void the warranty or be an issue with UL. He said they have tested Sanyo modules up to 1000 VDC with no problems.<br><br>As a final test on a system, I want to Megger test the array from the terminations at the inverter. The approach I'd plan to use is: <o:p></o:p></p><ul type=disc><li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l2 level1 lfo1'>Clamp the Fluke 1587 negative to the enclosuer ground. <o:p></o:p></li><li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l2 level1 lfo1'>Put the positive test lead to the negative conductor from the array and test <o:p></o:p></li><li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l2 level1 lfo1'>Put the positive test lead to the positive conductor from the array and test <o:p></o:p></li></ul><p class=MsoNormal>All tests would be done at 500 V. The modules are illuminated, but there is no significant reading from either positive or negative terminal to ground. <o:p></o:p></p><ul type=disc><li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l0 level1 lfo2'>The conductors would be removed from their terminals at the inverter and be in free air. <o:p></o:p></li><li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l0 level1 lfo2'>The conductors would be continuous through the string of 10 Sanyo 210 modules. <o:p></o:p></li></ul><p class=MsoNormal>My questions are: <o:p></o:p></p><ul type=disc><li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l1 level1 lfo3'>Does anyone see a problem in this approach? <o:p></o:p></li><li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l1 level1 lfo3'>Since the array often has 500 VDC open circuit readings and shows no indication of a fault whatever, would this test accomplish anything more than the standard voltage to ground tests I've already done? <o:p></o:p></li><li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l1 level1 lfo3'>Is there any danger to diodes or other PV components? <o:p></o:p></li></ul><p class=MsoNormal>Thanks in advance.<br><br>Drake <o:p></o:p></p></div></div></blockquote></div></div><p class=MsoNormal><o:p> </o:p></p></div></body></html>