I notice this is becoming more common.

Where when one has thunderstorms earth leakages trip. One then resets them, they go on first time but as soon as the lightning or thunder starts they trip again.

I have normally found that replacing the units helps due to the fact that over years the earth leakages become sesitive to lightning and thunder. But lately that does not even help.

One particular job in question:

They have over head LV lines in the area that bring the power in to the plots.

The earth leakages trip as stated above. I even went as far as to install two 3 phase earth leakages in the db that were connected on the supply side but had no conductors on the load side. This past weekend we had heavy thunder storms in JHB on Saturday and Sunday nights. Both those earth leakages were tripping.

I want to check the Loop impedance to see if that is to high. If that is high I would assume this could be adding to my problem because I have a bad earth.

Any other suggestions or thoughts?

As I say this is becoming very common.