Recommended voltage to set for insulation testing of PV array?

Hey guys,

What is the recommended voltage I should set for my insulation testing of PV array? Should it be 1000V or 500V? I have a Seaward PV Tester and am wondering which is the best practice for this.

If for example my total Voc for the PV array is around 800V+, should I be using 1000V?
If my Voc for the PV array is around 400V, should I be using 500V?

Thanks!

Comments

  • BB.BB. Posts: 27,698Super Moderators admin
    In general, "highpot testing" is done at the point of manufacture (for UL/NRTL Listed devices).

    In the US, our normal wiring for code is rated at 600 VAC (for DC, you can multiply by the square root of 2 = 849 VDC rated operating voltage).

    Factory Highpot testing would be 3x the rated value or 1,800 VAC / 2,546 VDC.

    I see that panels and wiring (for Europe) tends now to 1,000 VAC (?) rating... Which is higher than we normally see in the US... I do not know your wire/insulation/panel ratings used in your region (Singapore?).

    Normally, in the US, when using "Listed" components (wiring, boxes, panels, etc.)--We do not highpot test--We use standard construction practices to ensure that all is safe.

    If you do highpot testing in the field, you now have an entire string of wiring/panels/equipment that could fail your test--And then you will have to chase down the failure to find the fault and repair (typically insulation was cut on sharp edge--Possibly a burr on sheet-metal/conduit/not using proper wiring hardware for conduit fittings/etc.?). This could get expensive (labor). In general, using "Listed" components and good assembly practices is a better solution (old engineering/manufacturing saying--You cannot test in quality).

    Is this something required by your local code/regulations? I am not sure that field highpot testing is really a good practice.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Dave AngeliniDave Angelini Posts: 3,893Solar Expert ✭✭✭✭
    edited August 2016 #3
    sun_day said:
    Hey guys,

    What is the recommended voltage I should set for my insulation testing of PV array? Should it be 1000V or 500V? I have a Seaward PV Tester and am wondering which is the best practice for this.

    If for example my total Voc for the PV array is around 800V+, should I be using 1000V?
    If my Voc for the PV array is around 400V, should I be using 500V?

    Thanks!
    Is the Seward a model 150? Really nice meter!
    If VOC is 800V then your panels, wire, disco's are going to determine the setting on the megger. Off the record 1000V test setting but,
    Are you trying to meet the IEC 62446 standard for array testing?
    If so I would think a higher test voltage setting to be in compliance.

    As Bill said, good installation practice should not require a "megger" test but in many cases it is cheap insurance if many different people are involved in the installation. Who wants to go back to a remote job site? The following was an article that had good safety info also.


    Two major types of megohm-meters are available on the market today. The older style is a hand crank, analog meter; digital megohm-meters are also available. While both work well, the resolution on a high quality digital version is often better. Good megohm-meters start at around $600 and may run $3,000 or more depending upon the features desired. Fluke, Extech and Megger all make quality megohm-meters.

    The personal protective equipment required for Megger testing is generally the same as is required for troubleshooting ground faults: eye protection, insulating gloves and footwear, and a hard hat if the jobsite requires one. The one exception to the rule is that while 600 V-rated protective gear may be adequate for most work around PV systems, Megger testers generate up to 1,000 V. Make sure that your personal protective equipment ratings match the application.

    A Megger testing checklist involves these basic steps:

    • Ensure megohm-meter has batteries and is fully charged.
    • Lockout and tagout (LOTO) all power sources.
    • Disconnect both ends of the cable being tested.
    • Test the electrical insulation and record the results.

    Before performing megohm-meter testing, turn off the PV system or the section of the PV system that is being worked on. This may require LOTO procedures. Remember to apply LOTO to all energy sources; this may include inverters, disconnects or breakers.

    The suspect cable must be disconnected at both ends to ensure the megohm-meter does not damage any other equipment, such as internal electronic components of inverters or other devices. Once you disconnect the cable, use proper methods to ensure that the cable being tested is completely isolated from the ground and any other equipment. Many newer digital Meggers can detect any voltage between the conductors being tested and automatically disable testing while showing an alert. This is a useful additional safety feature.

    Refer to the owner’s manual for specific instructions for using any megohm-meter. In general, megohmmeters have two test leads: positive and negative. Connect the positive lead of the tester to the conductor being tested and the negative lead to ground. There are three voltage settings on most megohm-meters: 250 V, 500 V and 1,000 V. Unless otherwise directed, use the 1,000 V setting to test conductors. Most megohm-meters have a “Press to Test” button, which sends voltage into the cable only while the button is held down. Often there is also a manual lock switch that locks the power on for 3 minutes.

    Be sure to record all test results. It is a good idea to create a template for recording these results, with the step-bystep testing procedure spelled out for the electrician or technician. This template can also be used as a scope of work for an electrical subcontractor. The larger a system, the more cables there are to test. Be certain that all wires in the system are labeled. This will avoid confusion and unnecessary retesting.




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