Subject tests will be broadly grouped into three classes: acceptance, maintenance and fault location testing. Conducted on wire or cable after an installation however earlier than inserting it into service, an acceptance test detects set up or shipping damage that may affect cable performance. After the cable has been positioned in service, maintenance tests detect in-service deterioration. On the other hand, fault location tests pinpoint the precise failure site in a cable. Figuring out exactly where the cable has failed, permits the cable to be repaired or replaced as necessary. A number of of the most typical test strategies 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-energy antenna mounts. Normally carried out on 600-volt energy cable for both acceptance or maintenance functions, a megohm meter typically applies 600 to 2,500 V DC for several minutes to the cable. The megohm meter measures the present “leaking” by way of the insulation and displays the ends in items of resistance (i.e., megohms or hundreds of thousands of ohms). A reading less than 100 megohms indicates a doable cable problem. Regardless that Megger is a registered trademark of Megger Limited Group, the time period is widely used for all related tests regardless of manufacturer.
The hipot (high potential) test is an acceptance or upkeep test and is often used on cables rated 5 through 35 kV and higher. Just like the Megger test, this system applies DC voltage to a cable and measures present leakage via the insulation. Unlike the Megger test, the utilized voltage is considerably higher (as much as sixty five kV for a 15 kV cable, for instance) and the results are displayed in items of microamps (μA). With the hipot test, a high reading (for example greater than 100 μA) signifies a doable problem. Because of the doubtless lethal high voltages involved, this test must be performed solely by certified personnel.
The continuity test, which can be used on just about every type of wire and cable except optical fiber, might be the best and least expensive field test available. A handheld multimeter conducts the test by using a resistance setting to check the wire or cable for accidental contact between copper conductors as a result of damaged or faulty insulation. A multimeter can also be used to check for conductors which have been damaged somewhere alongside the cable’s length. The continuity test can be utilized for acceptance, upkeep or fault location testing.
A thumper is a fault location device that applies a high-voltage pulse to a cable to determine the exact location of a cable failure. It works by making use of a short (millisecond) high-energy pulse to the belden cable price list. At the point of the cable failure, the injected energy is launched with a loud bang much like that of a firecracker. When the test is carried out on cable buried a number of feet underneathground, a muffled thump is usually heard above ground. The cable is often thumped a number of instances a minute until somebody walking the size of the cable run can find the purpose of failure.