Identify Earth Leakage Faults

1/ is there a problem with RCD's tripping?

2/ are you qualified to do PAT testing?

Beware! In your case, you will also have a lot of triplen harmonic currents flowing thro the earth connection as the loads are PCs & UPS. Moreover, these PC Power Supplies would have filter circuits which could also filter ripples to earth. Advisable to use a good quality Power Quality Analyser.

Use ''Transmille 6080'' model PAT (Portable Appliances Tester). It can measure earth leakage current & ground resistance.

You have to just connect the plug of the instrument to the PAT and earthing wire from the instrument to the PAT (For class 1 test).

It will show wheather the test is passed or not (Pass means leakage current is under the safe limit) and will give the value of measured quatities. You can log all the details of the test done to a computer using it's software.

There is a new generation PAT tester, Gossen Metrawatt Secutest PSIII. It is a modern PAT that can even find the AC & DC components of earth leakage current.

Hi,

Thanks for the info. However, I would like to know what is involved in this test. Is it just determining the current (if any) flowing in the earth cable? Is it just that? Thanks

Basically PAT is measuring earth leakage current & ground resistance. If the earth leakage current is high, that appliance is not safe to handle. But in some PAT the features are extended. Using Gossen Metrawatt Secutest PSIII you can do the function test also. We can analyse the trivector power & pf.

Hi,

Thanks for the help.Now, I would like to know what I can do if I have no access to the actual device/instrument for measurement, can i use an ordinary multimeter to measure the current flowing through the earth line?

Furthermore, what would be the recommended/acceptable level of this earth leakage currents?

You can measure the leakage current by using a multimeter with clamp adapter (micrometer range). Whether your multimeter have this fascility?

Above 0.5mA a human will get the feeling of shock. Higher the current, higher the shocking effect also.

Various testing standards gives us the upper limit of leakage current.

Hi,

Yes, my multimeter has the micrometer facility. So, in your advice, if I measure current in earth cable to be more than 0.5mA, then I should recheck the circuit/wiring? And if it is less that 0.5mA, I can continue working?

Depending on where the computers are going to be installed or used, the allowable safe leakage currents will be a lot less than 0.5ma. In the U.S., hospitals and other patient environments follows certain electrical code requirements that are much stricter and a lot different than those used in a regular office or residential used appliances. UL 544 standards is one example of those standards that apply, which emphasis are on patient safety, and therefore has a much stricter leakage criteria to be followed.

Hi, Thanks for that. I shall look up the standards.

Various makes and models of electrical safety analyzers are readily available in the market today that you can use. Depending on make/ model, most have built-in filters to not be affected by any stray high frequency harmonics. Ordinarily measuring leakage currents (in micro-Amperes) flowing between equipment metal chassis to ground. Measurements can be done, with ground wire open as well as with the ground wire intact. Measuring ground conductor resistance (in milli-Ohm) and ground wire continuity, as well as an option to do ground integrity tests between power outlets grounding terminations and power plugs.