Discipline tests may be broadly grouped into three classes: acceptance, upkeep and fault location testing. Conducted on wire or cable after an installation but earlier than placing it into service, an acceptance test detects set up or shipping damage that might have an effect on cable performance. After the cable has been placed in service, maintenance tests detect in-service deterioration. Then again, 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. A few of the most common 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-power antenna mounts. Usually conducted on 600-volt energy cable for either acceptance or maintenance purposes, a megohm meter typically applies 600 to 2,500 V DC for a number of minutes to the Belden Cable Distributors. The megohm meter measures the current “leaking” via the insulation and shows the ends in units of resistance (i.e., megohms or thousands and thousands of ohms). A reading less than 100 megohms signifies a doable cable problem. Despite the fact that Megger is a registered trademark of Megger Limited Group, the term is broadly used for all similar tests regardless of manufacturer.
The hipot (high potential) test is an acceptance or maintenance test and is often used on cables rated 5 through 35 kV and higher. Like the Megger test, this machine applies DC voltage to a cable and measures present leakage by way of the insulation. Not like the Megger test, the utilized voltage is considerably higher (up to 65 kV for a 15 kV cable, for example) and the results are displayed in units of microamps (μA). With the hipot test, a high reading (for instance larger than a hundred μA) signifies a doable problem. Because of the possibly deadly high voltages involved, this test should be performed only by qualified personnel.
The continuity test, which can be utilized on virtually every type of wire and cable besides optical fiber, is probably the best and least costly subject test available. A handheld multimeter conducts the test by using a resistance setting to check the wire or cable for unintentional contact between copper conductors on account of damaged or defective insulation. A multimeter can be used to check for conductors which 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 system 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 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 carried out on cable buried several toes beneathground, a muffled thump is usually heard above ground. The cable is normally thumped a number of instances a minute till somebody walking the length of the cable run can locate the point of failure.