High Potential Test and Contact Resistance Test

This article is focused on contact resistance test and electrical high potential test.

High potential and contact resistance test for bus bar with circuit breaker

For contact Resistance, this test is aimed to measure the resistance of bus bar and for circuit breaker after being installed in the site to avoid high resistance which may be results from welding or installing in the site.

For high potential this test is aimed to measure and test the withstand of the insulations and isolators against the high voltage without break down.

Required equipment for Contact resistance test and High Potential test

  • Micro-ohm meter Contact resistance device.
  • High potential test kit.

High potential AC test

  • Insulation test by megger to test insulation by 5 kilo volt injection for 1 minute 3 phases line to line and line to ground.
  • Applying high potential AC voltage on the bus bar line to line and line to ground and the CB in service position, protection relays are energized and the VTs are racked out.
  • Applying high potential AC (higher voltage level than first applying time) voltage on the bus bar line to line and line to ground and the CB in test position, protection relays are energized and the VTs are racked out.
  • Take the record of passing current in mille Amperes from the high potential test kit.
  • Insulation test by megger to test insulation by 5 kilo volt injection for 1 minute 3 phases line to line and line to ground.
  • Compare the insulation test results to gathers before and after high potential test.

Contact resistance test connection

  • Contact resistance device has 4 leads, two for current and others for voltage, it depend on current injection on bus bar or circuit breaker then sense the voltage and calculate resistance by divide voltage on current (ohm’s law)
  • Check the BB torqueing of all bolted and confirm the torque value as per factory inspection.
  • Connect current leads between the device which you want to measure its resistance, connect voltage leads on the same terminals of current then adjust 100A injection then hold your hand on contact resistance push button, after few second the result will be displayed.
  • See figure below which shows connection of Contact Resistance Test.
contact resistance test

Contact Resistance Test

contact resistance test

Industry coded for Contact resistance test

NESC:               National Electrical Safety Code
NFPA:               National Fire Protection Association
NEC:                 National Electrical Code (2008 Edition)

ASTM:              American Society for Testing and Materials

IEC:                  International Electrical Commission
IEEE :               Institute of Electrical and Electronic Engineers

NETA :             National Testing Association

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1 Response

  1. October 4, 2019

    […] Measure transformer primary insulation with applicable over-potential tests see manufacturer’s instructions or refer to this article high potential test. […]

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