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PV String Current Measurement with a Clamp Meter — Solar O&M

2026年06月08日

An underperforming string hides in the array average. DC clamp measurement finds it fast.

Finding the Weak String

A solar array can lose several percent of its yield to a single underperforming string, and that loss disappears into the inverter's total. PV string current measurement with a DC clamp meter is the fastest field method to compare strings against each other and find the laggard — without disconnecting anything.

1. Why You Need a True DC Clamp

PV strings carry DC current, so an AC-only clamp is useless here. You need a Hall-effect DC clamp that reads true DC current and can be zeroed before measurement to remove offset.

  • True DC measurement, not AC-only.
  • Zero / relative function to null the Earth's field and offset.
  • Jaw large enough for the combiner-box cabling.
  • The EK-G645 measures AC + DC with a 52 mm jaw.

2. The Comparison Method

  1. Measure each string's current at the combiner box under stable irradiance.
  2. Strings on the same orientation should read within a few percent of each other.
  3. A string reading low is shaded, soiled, mismatched, or has a connection fault.
  4. A string reading zero has an open fuse, broken connector, or failed module.

3. Account for Irradiance and Temperature

String current scales with irradiance, so compare strings measured within the same short window under stable sun. A passing cloud invalidates a comparison taken minutes apart. Module temperature affects voltage more than current, but extreme heat still matters.

4. Following Up a Low String

  • Visually inspect for soiling, shading, and physical damage.
  • Check connector integrity and fuse continuity.
  • Measure open-circuit voltage to confirm module count.
  • Use a thermal scan to find hot cells or bad connections.

5. Safety with DC

PV DC arcs do not self-extinguish like AC. Never break a live DC connection under load. Measure with the clamp around an intact conductor, and follow lockout procedures before any disconnection.

EK Recommendation

The EK-G645 1200 A AC/DC clamp with zero function and true-RMS is ideal for PV string comparison and combiner-box work. Talk to EK service teams for a solar-O&M bundle including insulation and earth testing.