Determining Earth Leakage

With the discovery of a clamp that works as low as 1mA and fits around most main incoming cables (see here), using a Fluke 43B to measure Earth Leakage characteristics is now an exceptionally easy task.

Alongside is the screenshot of a domestic property.

It shows the level of leakage from all the filter capacitors on all the domestic appliances and a home computer. Also shown is the characteristics of the capacitors as they conduct the higher frequencies causing the waveform to become distorted.

Also of note is the Power Factor. Being nearly zero, this property has nearly pure capacitance causing the leakage. Although the VA is at 1.73, the power is negligible. Should the power have been higher (indicated by a relatively higher PF), this would have indicated a possible load has been accidentally strapped between Live and Earth (badly wired socket, etc.).

There are two things to note; The sign can be ignored as it is very dependent on the slight phase angle variation from both the clamp and imbalance polarity at this low current. At higher currents with a greater PF (closer to '1') then simply invert the clamp get the correct phase angle, although it makes no difference to the reading as such as it is the absolute value of the PF we are interested in.

Also, as one is working with capacitance and that higher frequencies are conducted better than lower ones, it is best to switch the instrument into Fundamental PF mode as opposed to True PF (known as Full PF on the 43B).

This is no more evident than when one switches to the harmonics screen. Although it would usually indicate the extent the earth leakage is conducting the voltage harmonic content through to the earthing system, it is a useful reading to do as it could also indicate any possible resonance (up to the 50th harmonic) that may be occurring between Live and Earth. Such resonance could be destroying EMC filters within sensitive electronic devices.

If there are any questions please ask.

Note: This web page does not form part of any official documentation.
Any information contained herein is used at own risk.

©  M.T.P. - 05.07.03