Murray Bridge Cable Sheath Fault Locator 5600V Auto Fault Point Cable Locator |

The cable sheath fault tester is designed based on the Murray bridge principle and can be used to locate breakdown points in various wires and cables, as well as defects that do not break down but have a low insulation resistance. The device uses an electric voltage regulator and an R-type transformer to form a high-voltage constant-current source, with push-button operation for voltage increase and decrease. It has a no-load voltage of 5600V and a short-circuit current of 100mA. It uses a high-sensitivity amplifier and a galvanometer to indicate balance, forming a balanced bridge with a proportional potentiometer, all at high potential. The measurement cable is a specially designed two-core high-voltage rubber cable, and a four-terminal resistance measurement method is used to eliminate errors introduced by lead resistance. The panel is maintained at low potential. The device also features a 12806 display and one-button operation: inputting the cable length automatically calculates the fault distance. The high-voltage source and the bridge are integrated into a portable protective case, so the device offers high voltage, is lightweight, easy to operate and safe to use.

The XHHG521B is positioned for technicians who want an instrument that automatically detects the fault point while keeping manual testing available for cross-checking. It is engineered for cable test and maintenance engineers who confirm the fault distance with the classic two-direction reverse-connection calibration (P1 + P2 = 100); for power supply bureau and industrial plant cable crews that need to measure the two-phase short-circuit fault of a cable line conveniently; and for teams that value a bridge with higher precision and stability and zero-position protection, where the cable length is entered and the distance is computed automatically on the display. It covers high-resistance linear breakdown points after installation (such as at cable intermediate joints), flashover breakdown points, and low-resistance defects that have not yet broken down. Unlike the other instruments in the same category, which pinpoint sheath faults on site or trace cable routes, this device is a MURRAY bridge that measures the cable fault distance itself, arranged at high potential and operated safely from the low-potential panel.

The cable sheath fault tester is particularly suitable for:

The cable fault location bridge method works as follows: the faulty phase and the non-faulty phase of the cable under test are short-circuited, the two arms of the bridge are connected to the faulty phase and the non-faulty phase respectively, and an adjustable resistor on one arm is adjusted so that the bridge is balanced; using the proportional relationship and the known cable length, the fault distance is obtained. The bridge method is relatively simple and its accuracy meets the requirements of on-site engineering testing, and it is very convenient for measuring a two-phase short-circuit fault of a cable line. Using the Murray bridge to locate a breakdown point is a classic approach, convenient and accurate, and its basis is that the conductor (or shielding-layer) resistance is uniform and proportional to the length. Let the distances from the two ends of the cable to the breakdown point be L1 and L2 and the total length of the cable be L, with corresponding conductor resistances R1 and R2; after balancing, L1 = P%·L, where P is the balance adjustment reading.

Wiring notes: HV is the high-voltage constant-current source; the faulty cable is CD and the auxiliary cable is AB, with the same conductor cross-section and the same length L, and the distance from the fault point to the measuring end is X; the measuring clamps are connected to the two ends A and C of the cable conductors, with the two sides of each clamp being the current and potential terminals, both reliably connected to the cable; R is the balance potentiometer, whose reading is a percentage; G is the galvanometer, with an adjustable electrical balance zero point; at the far end, the two ends B and D must be short-circuited and the short circuit must be reliable.

Preparation (judging the faulty phase and connecting correctly):

Measurement (raising the voltage to obtain the fault ratio):

Calculation (the fault distance is calculated automatically):

Reverse-connection calibration: lower the voltage and discharge, swap the measuring clamps, and repeat the steps to obtain another reading P2, which should give P1 + P2 = 100. The fault point position is X = 2 × L × P1%, and particular attention should be paid to the “2” in the formula, because the auxiliary cable doubles the cable involved in the calculation.

Other notes: sometimes interference affects the galvanometer zero point, in which case re-zero at the final sensitivity position (with the test voltage reduced to zero and everything else unchanged, zero it, then raise the voltage again and adjust the balance for a more accurate value); when conductors of different cross-sections are used as the auxiliary cable, convert to the length of the faulty cable, so if the faulty cross-section is Sx and the auxiliary cable is S, the formula becomes X = P1% × (1 + Sx/S) × L; if all three cores of a three-core cable have broken down or are short-circuited with each other, a core with the best insulation resistance can be selected as the auxiliary cable. Understanding the factors affecting sensitivity helps: the larger the current through the bridge, the higher the sensitivity; the larger the cable conductor resistance, the higher the sensitivity, meaning thin and long cables have higher sensitivity while thick and short cables have lower sensitivity, so for cables of large cross-section and short length the current should be increased as far as possible and a higher amplifier sensitivity used.

Warranty: within one year from the date of purchase, free repair is provided for product quality problems, with lifetime maintenance and technical service.

It is a cable sheath fault tester designed on the Murray bridge principle, used to locate breakdown points in various wires and cables as well as defects that do not break down but have a low insulation resistance.

The no-load voltage is ≥5600V, the short-circuit current is ≥100mA (5-40mA recommended for balancing), the positioning accuracy is ±(0.2%·L±1) meter, the weight is 25kg, and the power supply is AC 220V (±10%), 50Hz±1Hz with an 8.4V internal battery.

It automatically detects the fault point but retains manual testing functionality. The cable length is entered on the 12806 display and the fault distance is calculated automatically, and the result can be cross-checked with the classic two-direction reverse-connection calibration where P1 + P2 = 100.

The instrument cannot be started when the voltage adjustment is not at the zero position; at least two people must be present; the grounding terminal must be reliably grounded; before touching high-voltage parts a person must discharge first and hang up the ground wire; and the automatic fault-distance calculation must be carried out in the non-boosted state.

The packing list includes the main unit (1), high-power jumper cables (1), power cord (1), ground wire (1), charger (1) and fuse 3A (5). The product is warranted for one year from the date of purchase with lifetime maintenance.