Discipline tests could be broadly grouped into three classes: acceptance, upkeep and fault location testing. Carried out on wire or cable after an set up however earlier than placing it into service, an acceptance test detects set up or shipping damage that might affect cable performance. After the cable has been placed in service, maintenance tests detect in-service deterioration. Alternatively, fault location tests pinpoint the precise failure site in a cable. Knowing precisely where the cable has failed, permits the cable to be repaired or changed as necessary. A few of the most common test methods are described below.
A Megger test uses a megohm meter to test the insulation properties of such things as electrical wiring, motor windings and high-power antenna mounts. Usually carried out on 600-volt power cable for either acceptance or upkeep functions, a megohm meter typically applies 600 to 2,500 V DC for a number of minutes to the cable. The megohm meter measures the present “leaking” via the insulation and shows the ends in items of resistance (i.e., megohms or millions of ohms). A reading less than a hundred megohms indicates a potential cable problem. Despite the fact that Megger is a registered trademark of Megger Restricted Group, the time period is broadly used for all similar tests regardless of manufacturer.
The hipot (high potential) test is an acceptance or maintenance test and is normally used on cables rated 5 by 35 kV and higher. Just like the Megger test, this machine applies DC voltage to a cable and measures present leakage by way of the insulation. Unlike the Megger test, the utilized voltage is considerably higher (up to 65 kV for a 15 kV Belden Cable Equivalent Manufacturer, for example) and the outcomes are displayed in models of microamps (μA). With the hipot test, a high reading (for instance better than 100 μA) signifies a possible problem. Because of the possibly deadly high voltages concerned, this test must be performed only by certified personnel.
The continuity test, which can be utilized on nearly each type of wire and cable besides optical fiber, might be the simplest and least costly subject test available. A handheld multimeter conducts the test through the use of a resistance setting to check the wire or cable for accidental contact between copper conductors due to damaged or faulty insulation. A multimeter will also be used to check for conductors that have been damaged somewhere alongside the cable’s length. The continuity test can be utilized for acceptance, maintenance or fault location testing.
A thumper is a fault location machine that applies a high-voltage pulse to a cable to find out the exact location of a cable failure. It works by making use of a quick (millisecond) high-energy pulse to the cable. On the level of the cable failure, the injected energy is released with a loud bang much like that of a firecracker. When the test is performed on cable buried several toes belowground, a muffled thump is normally heard above ground. The cable is often thumped a number of occasions a minute till someone strolling the length of the cable run can find the point of failure.