How to test instrument leak voltage

Hi all,

Actually I have an instrument to detect component failure.
Which is operated at 230V AC @50HZ. Instrument properly connected earth..when I test earth to neutral voltage it's around 3V AC..
Kindly suggest me how to test the instrument leak voltage..
Is it right way to test the voltage of instrument body to neutral when the instrument earth disconnected criteria?..

Awaiting for your positive feedback..

Earth should be never disconnected if the instrument is equipped with protective earth connection. Instrument safety is checked by measuring the earth and isolation resistance.

What do you mean with "instrument leak voltage"? IMHO it's no known term in electrical safety.

dsanthosh67 said:

Hi all,

Actually I have an instrument to detect component failure.
Which is operated at 230V AC @50HZ. Instrument properly connected earth..when I test earth to neutral voltage it's around 3V AC..
Kindly suggest me how to test the instrument leak voltage..
Is it right way to test the voltage of instrument body to neutral when the instrument earth disconnected criteria?..

Awaiting for your positive feedback..

Click to expand...

I don't know what you mean earth to neutral voltage. You need to be more specific how you measure. Do you mean (1) you measure on the wall plug the Earth ground and the low side of the two other prong? Or (2) do you mean you measure the instrument ground to the earth ground?

For (1), it's your wall plug issue, I don't know enough to tell you.

(2) If the instrument ground is isolated from the earth ground ( which a lot of instrument do), you cannot just measure the voltage between them, the voltage you measure across them is the voltage across the input impedance of your meter from the leakage current. Usually it's the leakage current we worry about. Before I go any further, please specify how you measure first.

Neutral and earth should not be connecte together inside a product

they are connected at the local DB ( distribution board ) - if you are seeing 3Vac across earth to Neutral at a wall socket - then you have a lot of neutral current causing this ( not that uncommon )

Usually a "Megger" is used to test insulation from P & N to earth ...

Pls find the attached image for your reference. Which I have tested in two different multimeter..Here I have noted eractic values which is right or wrong?.
I'm looking to ensure the instrument does not generate any leak voltage or shock free instrument..

Some information missing. What's the instrument application class? Is it class I, case with protective earth connection or class II, double insulated without protective earth connection?

Your post #1 suggests class I, in this case the instrument must not be operated with disconnected earth. If you have disconnected the protective earth of a class I device, the measured neutral to body voltages are just normal operation. Filter capacitors between protective earth and line/neutral cause a leakage current and respective voltage drop at high impedance voltage meters.

FvM said:

Some information missing. What's the instrument application class? Is it class I, case with protective earth connection or class II, double insulated without protective earth connection?

Your post #1 suggests class I, in this case the instrument must not be operated with disconnected earth. If you have disconnected the protective earth of a class I device, the measured neutral to body voltages are just normal operation. Filter capacitors between protective earth and line/neutral cause a leakage current and respective voltage drop at high impedance voltage meters.

Click to expand...

FvM said:

Some information missing. What's the instrument application class? Is it class I, case with protective earth connection or class II, double insulated without protective earth connection?

Your post #1 suggests class I, in this case the instrument must not be operated with disconnected earth. If you have disconnected the protective earth of a class I device, the measured neutral to body voltages are just normal operation. Filter capacitors between protective earth and line/neutral cause a leakage current and respective voltage drop at high impedance voltage meters.

Click to expand...

As per instructions our instrument surely meets in CLASS I. If I disconnected the protective earth and measure what will be the average voltage between the body to earth. When i measure in this case different multimeter will shows different voltage.Pls refer the attached image in previous post. I don't know this will be right procedure to measure voltage between earth vs body when disconnected earth..
Kindly suggest me my ultimate aim is to confirm that the instrument does not have any shock even the earth disconnected..

The voltage measurements with disconnected earth are meaningless and can show any value. Instead you need to measure the insulation resistance and earth continuity. Optionally leakage current.

FvM said:

The voltage measurements with disconnected earth are meaningless and can show any value. Instead you need to measure the insulation resistance and earth continuity. Optionally leakage current.

Click to expand...

Thanks for your valuable information..pls explain from which two points I need to measure the insulation resistance?
Earth continuity is between earth pin in power socket to the instrument case right?

Insulation resistance is measured between protective earth and shorted L and N terminals with high voltage, e.g. 500 VDC. Power switch must be on.