In our modern, connected world, increased demands are placed on all aspects of electrical circuitry. Years ago, measuring low resistance down to 0.01 ohms was acceptable, but with today’s industry standards, test engineers and technicians are now required to make repeatable measurements within a few micro-ohms or less.
Low resistance measurements—from a four-wire low resistance ohmmeter—identify restrictions in current flow that might prevent a machine from generating its full power or provide insufficient current flow needed to activate protective devices in the case of a fault. To prevent long term damage and minimize energy wasted as heat, incorporate routine low resistance testing into your plant’s preventative maintenance program.
By assessing and recording your equipment’s initial condition, you can use periodic testing to identify unexpected changes in measurements—trending the data to help forecast possible failure conditions in the future. Excessive changes in measurements point to the need for corrective action. It’s important to keep clear records of results and conditions under test, so you can create a database and easily identify any changes from fatigue, corrosion, vibration, temperature, or other condition that can occur at the test site.
When taking measurements below 1 Ohm, it’s essential to use test instruments that will minimize errors introduced by the test lead resistance or the contact resistance between the probe and the material under test. To compensate for these potential errors, you’ll need a low resistance tester equipped with four terminals, a reversible test current, and a suitable Kelvin Bridge meter.
Since developing the original DUCTER™ low resistance ohmmeter in 1908, Megger has led the way in low resistance testing. Today, our family of digital low resistance testers—DLROs—range in test currents from 0.5 mA to 200 amps to fit your specific application needs.
For industries that consume vast amounts of electrical power or have critical specifications on bond connections—including power plants, chemical plants, refineries, mines, railroads, utilities, and aircraft or automotive manufacturers—low resistance measurements are a requisite component for any maintenance plan.
Joints carry current that will heat up over time, but the amount of heat is dependent on the resistance of the connection, the current it carries, and the time frame. Once a joint or cable connection becomes hot, it will only become hotter—unless you identify it with a thermal imaging camera. But without a direct line of site to the connections, you can’t use a thermal imager. In these cases, you won’t know about a bad connection until the lights (or power) go out, as the connection burns out and the protective device goes off.
Fortunately, you can use a low resistance ohmmeter to check the contact resistance of switchgear, lapped joints on busbars, and cable lug connections before the power is switched—the only way to completely prevent poor connections from becoming potentially catastrophic failures.
See our full line of Low Resistance Ohmmeters