Recommended voltage to set for insulation testing of PV array?

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!

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.