Leakage Clamp Meter
|The MEWOI Leakage Clamp Meters Way To Use|
Let's go back to the customer's problem. If the RCD trips, it should be temporarily "bridged out". The contractor now simply clamps the Leakage Clamp Meter around both phase and neutral conductors on the supply side of the RCD(for 3-phase systems, all three live conductors and the neutral conductor should be enclosed).
The instrument display will then directly read the leakage current to earth in the installation with a high resolution.
Suppose the display reads 43.5 mA, simply tracing the leakage current the fault will be found.
In the fig below there is a practical example how to trace the fault measuring the leakage current.
Normally, using this tracing system the fault will be found but sometimes the earth leakage current will not be caused exclusively by low insulation resistance.
In fact could happen that performing an insulation test there is not a low value of insulation resistance even if the RCD still trips!
|High Frequency Selector Switch|
This switch is designed to select "WIDE" or "50/60Hz" range. "WIDE" range covers a wide frequency band of 40Hz to 1kHz. AC current having a fundamental waveform and harmonics can be measured over this range. "50/60Hz" is restricted to a frequency response of 40Hz to 100Hz and therefore permits measurement of AC current of fundamental frequency only by filtering harmonic content. When in doubt as to the presence of harmonics you can identify it by using this frequency selector switch. To give an example, the following shows the results of AC current measurement on an earthing wire within a switchbox where there is an inverter based airconditioner is connected at summertime. Model 2433 reads 56mA AC with the frequency selector switch set at the "WIDE' position as shown, while it displays 3mA at the "50/60Hz' switch position. The difference between the two readings (56mA - 3mA = 53mA) is considered leakage current caused by harmonics. The test also found that this leakage current is flowing in o single phase, 3-wire circuits other than those connected with the inverters in the building inspected.
"WIDE"range - 56mA reading
"50/60Hz"range - 3mA reading