Your project is almost built! Raceways are installed and cables are pulled. What now? Do we terminate the cables and walk away?
Not quite...
After initial construction, we're still left with commissioning. Commissioning is the process of verifying the quality of an electrical installation prior to full energization. What are the activities involved with commissioning? It depends on the installation.
Let's start off with a simple installation, like in a home. In this case, after wires are pulled the next step is usually just to terminate, do a visual check of the installation, and check out the wiring to make sure it works as intended. That's some really minimal commissioning.
What about on a bigger project? What then? Here are some usual commissioning activities employed on larger projects:
Continuity Testing: Continuity testing checks a circuit to make sure that the connection between two points is electrically continuous. In other words, the impedance between those two points, as measured by an Ohmeter, should be very low. Digital multimeters generally possess a continuity function designed specifically for continuity testing. The continuity test makes an audible noise when continuity is established.
Insulation Resistance Testing: Insulation resistance testing, also known as Megger Testing, measures the resistance between a phase (current-carrying) conductor and its insulation. This testing can be performed on equipment or circuits. Megger testing can be performed with special multimeters at low voltage levels. Medium and high voltage equipment and cables require dedicated equipment for this purpose. The results of an insulation resistance test should be on the order of MegaOhms, with approximately 1 MegaOhm of resistance per 1 kV of nominal voltage level.
Hipot Testing: An abbreviation for "high-potential" testing, Hipot tests use a high voltage to measure the ability of a conductor at medium or high voltage to withstand surges. Hipot tests are a PASS/FAIL test. A leakage current is measured when the high voltage is applied between phase conductors, and, if the leakage current is too high, the test fails. Hipot tests used to be performed using DC voltages, but this would lead to static charge built up on cables due to higher cable capacitance at medium and high voltage (from shields, etc.). Now, Hipot tests are done with very-low-frequency AC voltages, known as VLF testing, to mitigate this issue.
Partial Discharge Testing: Partial discharge (PD) testing takes the concepts in a Hipot test one step further. A PD test applies a high voltage and assess the leakage characteristic of the cable across its entire length. PD tests tell the tester where failures are, providing more detail than a Hipot test.
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