Electrical Testing
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Tip of the Week: Is that test really necessary?

Make sure the tests you carry out are the ones that will provide the information you're seeking.

Do you use test equipment that is appropriate for the test being conducted? Or do you try to make one instrument do all kinds of jobs? Do you perform tests that are not even necessary?

Consider the case of an electrician who perhaps had too much appreciation for his insulation resistance (IR) tester. Large portions of the equipment grounding conductor (EGC) in his plant consist of insulated conductors. So he conducted IR testing on these conductors.

Although that testing does allow predicting when that insulation will fail, it’s also true that the uninsulated raceway in this same plant is part of the EGC. That EGC insulation probably did not need to be tested.

Does this mean you don’t do any testing on the EGC? The purpose of the EGC is to provide a low-resistance ground-fault current path [see NEC Art. 100], thereby allowing protective devices to open when there’s a fault. It connects normally non-current carrying metal parts of equipment together and to the system grounded conductor or to the GEC, or both. So it’s pretty important.

Visual inspection is part of good preventive maintenance practices for the EGC. In many facilities, the connections are tested using a digital low resistance ohmmeter (DLRO). You wouldn’t use a DLRO to test your conductor insulation, and the IR tester isn’t the tool for testing EGC connections. You need both tools and the understanding of how to use them to achieve the desired goal.

And, of course, your handy and useful digital multimeter is the wrong tool to use for either job (unless it’s a combo unit with these specific functions included).

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