The 275 HP is a high voltage proximity detector. It has eight voltage detection settings from 240Vac to 275kVac. The 275 HP consists of an internal pickup sensor plate, a sensitivity selector, a visual and a sound annunciator. With the 275 HP, physical contact with electrical conductors is not necessary when testing for live lines. This 275 HP works by proximity. Its sensor senses the radiated field which surrounds live conductors. Radiated field strength increases with voltage and decreases quickly with distance or earth shielding. The radiated field from a cable of closely bunched conductors supplied by three phase power tends to cancel (See “Limitations of use” paragraph). Detecting distance of a 250Vac single live wire is approximately 10cm. With a bunched neutral and earth cable, as in a flexible cable, the distance is reduced to 5cm. Some of the typical uses are : identify and check live cables ; find fault in flexible cables ; check earth equipment ; service neon lightning ; trace live wires ; check high frequency radiation ; detect residual or induced voltages.
For example, faults in damaged flexible cables are found by applying low voltage to each conductor. Earthing the remainder and moving the tester along the cable until the change in condition is obtained. (Flexible cables which are used in mining and building industries, are readily repairable when the break in the cable is located.) When testing for high voltage, the rotary switch (attenuator) is used to identify and differentiate various H.V. live cables. The detector must be used in conjunction with a long and insulation rod when measuring high voltage (kV). However, the 275 HP is a non-contact tester and it is advised that the tester should never come into contact with cables (kV) as this tester is merely a non-contact AC proximity detector. Checking or proofing the tester is easy. Switch the sensitivity to 240V and place the dome against a low voltage live conductor or rub the dome with a cloth or against an item of clothing as this generates a static DC which triggers the detection of circuit. The light and beeper should go “on” as if a live wire is being.