Earth faults are common fault condition in an electrical system. This will get noticed suddenly on a raining day. Once earth fault is detected it is Electrical Engineers headache to find the cause of earth fault. It can be a faulty device or a loose wire or wet terminal block. It is very important to locate the position of the earth fault and the reason for it.
In my experience a live line checking is easy. It is easy to go from the higher end. Go to the main distribution board and switch off all loads on by one. When you switch off one load the earth fault indication will vanish. (If it is not vanishing after switching off all individual feeders then the cause can be inside the panel or there can be multiple faults. To locate multiple faults you have to switch off all feeders and switch on loads one by one).
Once you have identified one feeder go down with that feeder. If it is a sub distribution board repeat the exercise and find out the affected feeder. If it is a motor starter check the starter without motor and later the motor. Once you have pin pointed the location it is easy to find the reason for the fault. For complicated systems you have to isolate individual systems and locate the location. Make groups of three or four items and remove supply to that line.
Remember it is important for any system to clear off earth faults before a second fault occur. So be fast in tracing the fault.