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Connecting your Insulation Test Set

DC Hipots and Megohmmeters are fairly common test sets used by test technicians and engineers.  The basic operation for both a DC Hipot and a Megohmmeter is the same; a known DC voltage is applied across insulation.  The applied potential causes several small currents through and over surfaces of the insulation being tested. The total current is measured and the result is displayed as either an ohmic value or as a current value.

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With modern insulating materials there is little, if any, difference in the reading obtained, regardless of which way the terminals of the test set are connected.  However, did you know that it is industry standard to connect the positive (+) lead to ground?  In fact, the output polarity of DC Hipots is designed to be negative polarity, positive ground.

The reason for this is that on older insulation, a little known phenomenon called electroendosmosis (i′lek•trō¦en•däs′mō•səs) causes a lower insulation reading to be obtained with the positive terminal connected to the grounded side of the insulation being tested.  Since insulation testing is typically concerned with safety, maintenance and /or troubleshooting the worst case reading would be the one which yields the most relevant information.

Along with DC Hipots and Megohmmeters, cable fault locating equipment such as Surge Generators (thumpers) also use a negative output with reference to ground.


Related electrical test equipment available for rent from Protec:

High Voltage PTS-80 80kV DC Hipot with Megohmmeter

HV Diagnostics HVA30 30kV VLF / DC High Voltage Test Instrument



This electrical test equipment is available for rent, lease, or purchase from Protec Equipment Resources. We are here to help you with your testing equipment needs.

Wherever the job takes you (and the equipment), with Protec’s multiple locations, we always ship from the office closest to your desired drop location (if the electrical test equipment you need is in-stock at that location), and the equipment can be returned to the nearest office.

We always consider ALL shipping options in order to save you the most time and money.

Also, if you happen to be close to one of our many office locations, walk-ins are always welcome!

Rely on the Electrical Test Equipment Rental Experts, we are there when and where you need us.

Editor’s Note: This post was originally published March, 2012 and has been updated freshness, accuracy and comprehensiveness.


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