What are the reasons for Earth leakage current in CNC Machine?

What is CNC stand for,dear?.

@ Mr.Omer A.Osman : computer numerical control (CNC)

If your question about the protection, the earth leakage is required for human protection against indirect contact .
If you are questioning about the phenomenon it self, in simple way the Earth leakage current is the current passing through Earth,CPC,externeous conductive parts to complete the circuit. ie current that complete the circuit with means other than the circuit conductors (Line/Neutral).

We are faceing a problem in our customer CNC machine. there was continous trip in machine. hence we chaged Fuse rating in ELCB. After tat issue was resolved. But we want to find the reason for this problem. Pls help Ji...

You very likely have a neutral conductor from the power supply, or from a motor, connected to the frame of the machine, and a separate protective earth connected to the building earthing system, creating some double path for neutral currents.

Dear Kummar, usually ELCB is now replaced by RCD which operates in the principle of current balance (Line & Neutral). It is classified as a Cicuit Breaker,No fuse associated therein,accordingly.

Since you have confirmed that the rating of the Fuse feeding the aforementioned M/C has been upgraded, I gues the reason is that the rating of the protective device was under estimated. ie simply, was blown due to sustainable overload .

Note: if the fuse was used in accordance to BS3036 "re-wirable fuse", a correction factor of 0.725 ought to have been applied. ie the operating current of this type of uses does not equal 1.45In as per standard.