[RE-wrenches] Insulation testing
Chris Anderson
CAnderson at borregosolar.com
Thu Sep 17 08:34:46 PDT 2009
I believe you mean 2200v?
I did see this formula in the aforementioned Fluke report, but was cautions about going that high as it seemed unnecessarily higher than the voltages we would ever see in PV and from a pragmatic standpoint, the reasonable priced Meggers seemed to only go up to 1000v.
-Chris Anderson
Chief Technology Officer
Resources Group
C: 603-732-2411
Borrego Solar Systems
From: re-wrenches-bounces at lists.re-wrenches.org [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Joel Davidson
Sent: Wednesday, September 16, 2009 8:43 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] Insulation testing
Hello Chris,
Nicely summarized. Thank you. I megger to the UL 1703 standard for module hi-pot testing is 2X system voltage plus 1000 volts. For example, 600 volts X 2 + 1000 = 1200 volts.
Best regards,
Joel Davidson
----- Original Message -----
From: Chris Anderson<mailto:CAnderson at borregosolar.com>
To: RE-wrenches<mailto:re-wrenches at lists.re-wrenches.org>
Sent: Wednesday, September 16, 2009 11:19 AM
Subject: Re: [RE-wrenches] Insulation testing
I would like to put forward our commissioning test procedures with regard to voltage and insulation testing for comment and to share if others are trying to tighten up their commissioning procedures. I would love to hear Bill's feedback and any input others might have into our process and areas where we might be exposed.
Thanks in advance for your comments.
Sequence and Procedures for
Quality Assurance Testing and System Commissioning
Quality Assurance Testing
o Source Circuit Testing - Voltage and continuity to ground of all strings
* Test conditions:
* Testing to be done at the combiner boxes
* Modules are connected to the home runs
* Positives are landed on the fuse block, but fuses are not yet installed in the CB
* Negatives are cut to length and labeled but not landed in the CB
* Ground is connected in a continuous path to the racking and modules and is landed in the CB
* Test
* Check for voltage between each positive and all negatives - record voltages for each strings and confirm no voltage between strings of different numbers, simultaneously verify polarity as recording voltages
* Check for voltage between each positive and ground - record voltage (should be 0)
* Check for voltage between each negative and ground - record voltage (should be 0)
* Complete the first half of the combiner box commissioning worksheet - noting weather, time of day etc.
* After the test is complete
* Each negative can be landed on the negative block in the CB
* Test continuity of fuses and insert into holders - DO NOT CLOSE
o Output Circuits - Insulation testing of wires from CB to Inverter and verification of polarity
* Test conditions:
* Testing to be done at the inverter
* All wires are run in conduit, cut to length, labeled, spliced if applicable and conduit covers are on from combiner through to inverter
* Only the ground wires are landed in both the CB and the inverter
* The GFDI fuse is removed from the inverter
* All conductors are taped off at the opposite end of where the Megohmeter will be attached and are safely isolated to prevent touching of anything and in a safe position to be energized
* Test
* Megger test all wires to ground at 1000Vdc
* Megger test all wires that share a conduit at any point in the system to each other at 1000Vdc
* record all values and troubleshoot any wires that have a reading under 100 M Ohms corrected for Temp and humidity
* If under 100 M Ohms requires investigation and may require replacement of the wire
* After the test is complete
* Land the positive and negative at the combiner box
* Close one fuse holder at CB1 and close the integrated CB/rooftop DC disconnect protecting the output of the CB
* test for voltage and polarity between the positive and negative output circuits from CB1 at the inverter and verify that they are properly labeled
* Open the CB/rooftop DC disconnect and then open the fuse holder in CB#1
* Verify that the voltage has bled down to zero then land the positive and negative wires for this combiner box at the inverter
* Repeat steps for each CB until all polarity and wire locations are identified and landed
* Once all the positive and negative wires from the CB's are landed, if applicable test continuity of the fuses at the inverter disconnect and insert into holders
o AC Wiring Circuits - Insulation testing of wires from AC Tie in point (POCC) to Inverter and verification of phasing
* Test conditions:
* Testing to be done at the inverter
* All wires are run in conduit, cut to length, labeled, spliced if applicable and conduit covers are on from AC Point of Connection through to the inverter
* Only the ground wires are landed in both the Main Service Panel and the inverter
* The GFDI fuse is removed from the inverter
* All conductors are taped off at the opposite end of where the Megohmeter will be attached and are safely isolated to prevent touching of anything and in a safe position to be energized
* Test
* Megger test all wires to ground at 1000Vdc
* Megger test all wires that share a conduit at any point in the system to each other at 1000Vdc
* record all values and troubleshoot any wires that have a reading under 100 M Ohms corrected for Temp and humidity
* If under 100 M Ohms requires investigation and may require replacement of the wire
* After the test is complete
* Land the conductors in the inverter being sure to follow the inverter manufacturer's guidelines for torque settings and use a permanent marker to create a straight line across the screw indicating the proper torque setting
* This test will likely be completed before the building shut down to interconnect the system. Do not land the conductors at the AC tie-in point until the panel has been properly de-energized
* After the Service Panel or tie-in point is de-energized, land the conductors at the AC tie-in point. Be sure to follow the manufacturer's guidelines for proper torque settings and use a permanent marker to create a straight line across the screw indicating the proper torque setting.
o Connection testing
* Test conditions:
* Testing to be done at all locations
* All wires are landed
* Test
* Test all wires for proper torque settings - refer to manufacturer installation manual
* Physically tug on all wires for a visual inspection of loose connections
NOTE - All conductors #4 and larger should be marked with a straight line on the screw once they have been tightened to the appropriate setting
* After the test is complete
* Close all fuse holders at each combiner box
* Close all DC disconnects associated with each combiner box
System Commissioning
o You are now ready to Commission the inverter
o Follow inverter manufacturer commissioning procedures
o Complete the balance of the combiner box commissioning worksheet, the initial start up and inverter commissioning worksheet
* Imp Testing of source circuits
* Test conditions:
* Testing to be conducted at combiner boxes
* System is up and running
* Test
* At each combiner box, check for operating current of each string by placing a clamp meter around each positive source circuit - record the value on the combiner box commissioning worksheet
* Simultaneously record the irradiance value at the plane of the module for the strings of which you are testing
* Repeat for all strings in the combiner box
* Imp Testing of output circuits
* Test conditions:
* Testing to be conducted at the inverter
* System is up and running
* Test
* Check for operating current of each CB output circuit by placing a clamp meter around each positive wire - record the value on the inverter commissioning worksheet
* Simultaneously record the irradiance value at the plane of the representative modules for the combiner box of which you are testing
* Repeat for all output circuits from each combiner box
-Chris Anderson
Chief Technology Officer
Resources Group
C: 603-732-2411
Borrego Solar Systems
From: re-wrenches-bounces at lists.re-wrenches.org [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of David Palumbo
Sent: Monday, September 14, 2009 10:58 PM
To: 'RE-wrenches'
Subject: Re: [RE-wrenches] Insulation testing
I'd like to see if we can complete the thread on insulation testers (Meggers). Below is a copy of Bill Brooks last posting on this subject from several weeks ago.
Bill says the keys are to use the tester and in "performing the tests properly and safely which requires test procedures". What are the proper testing procedures? We have a Fluke 1503 and the information that came with it is not very helpful in setting up a testing procedure. The DVD that came with it is more of a sales tool on why you should have the tool. We already have the tool. We want to know how to use the tool. Can anybody give advice on this?
<< I bought two insulation testers (Megger is a brand name) in April. A used
Fluke 1520 off Ebay for $275 and a new inexpensive (cheap) insulation tester
on Amazon (Electronic Specialties 550 Insulation Tester for $162). Both work
fine. The Fluke has better accuracy that I need for very specialized "field
wet resistance testing" (FWRT). However, the cheap tester works great for
finding faults in conductors and severe faults in modules.
I bought both to determine if a cheap meter would work and the answer is
YES. The key is performing the tests properly and safely which requires test
procedures. The other key to actually use the tester. Several people own
these devices, but never use them. They should be used on every installation
after the wire is installed to determine if any wire damage is visible to
the tester. Even though this will not solve all field mistakes, it will
catch the marginal problems that may be too small to be detected by the GFP
circuit in the inverter.
Bill. >>
David Palumbo
President, Independent Power LLC
462 Solar Way Drive, Hyde Park, VT 05655
NABCEP Certified
www.independentpowerllc.com
(802) 888-7194
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