Subject tests can be broadly grouped into three classes: acceptance, upkeep and fault location testing. Conducted on wire or cable after an installation however earlier than inserting it into service, an acceptance test detects installation or shipping damage that may have an effect on cable performance. After the cable has been placed in service, maintenance tests detect in-service deterioration. Alternatively, fault location tests pinpoint the exact failure site in a cable. Understanding precisely the place the cable has failed, permits the cable to be repaired or replaced as necessary. Just a few of the commonest test methods are described below.
A Megger test makes use of a megohm meter to test the insulation properties of such things as electrical wiring, motor windings and high-power antenna mounts. Usually conducted on 600-volt power cable for both acceptance or maintenance 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 current “leaking” by the insulation and displays the leads to items of resistance (i.e., megohms or millions of ohms). A reading less than a hundred megohms signifies a attainable cable problem. Despite the fact 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 maintenance test and is often used on cables rated 5 by way of 35 kV and higher. Just like the Megger test, this gadget applies DC voltage to a belden cable finder and measures present leakage by means of the insulation. In contrast to the Megger test, the applied voltage is considerably higher (up to 65 kV for a 15 kV cable, for instance) and the results are displayed in models of microamps (μA). With the hipot test, a high reading (for example larger than a hundred μA) signifies a doable problem. Because of the doubtless lethal high voltages concerned, this test have to be carried out only by qualified personnel.
The continuity test, which can be utilized on nearly every type of wire and cable except optical fiber, is probably the best and least expensive discipline test available. A handheld multimeter conducts the test by utilizing a resistance setting to check the wire or cable for unintentional contact between copper conductors as a result of damaged or defective insulation. A multimeter can be used to check for conductors that have been broken somewhere along the cable’s length. The continuity test can be used for acceptance, upkeep or fault location testing.
A thumper is a fault location machine that applies a high-voltage pulse to a cable to determine the exact location of a cable failure. It really works by making use of a brief (millisecond) high-energy pulse to the cable. At the level of the cable failure, the injected energy is launched with a loud bang just like that of a firecracker. When the test is performed on cable buried a number of ft underground, a muffled thump is normally heard above ground. The cable is often thumped several times a minute till somebody strolling the size of the cable run can locate the purpose of failure.