Had 2 electricians round to diagnose this fault and neither one can. In Johannesburg we get almost daily electrical storms in the summer (October - March) and this summer our ELU trips whenever there is a storm. The strike can be miles away and we still trip. This did not happen in previous seasons.

So far, the ELU has been replaced with successively superior (allegedly) components. A surge arrestor has also been installed on the DB. Nothing has helped.

The fault is not moisture related, as for example yesterday a strike about 7 seconds away (over 2 kms) caused a trip even though there was no rain.

Is it possible for a phone line to cause the earth leakage to trip? If not what else could be causing it?

Tell us more... is this an Earth Leakage Relay?
And you're in South Africa?
Is this a commercial facility or residential?

It's my house, and apologies but I'm no electrician myself. Yes I'm in South Africa, and this is the earth leakage unit that trips in every storm.

Some history - earlier this year the old earth leakage unit (ELU) burnt out, was replaced and this was the suspect. However this has now been replaced twice and both replacement units have the same fault. The surge arrestor installed before trying any additional ELUs has also not stopped the problem.

My neighbours do not have the same problem.

Based on what I have been able to find on the net,
This is essentially a "ground fault interrupter"...
I would suggest the grounding system of your electrical service be verified to be
Correctly installed and connected. (also the ELU connections) You may consider improving you're grounding electrodes...
I am interested in why you are having issues and your neighbors are not... do they
Have the same ELU equipment and connections? Are their electrical services newer or older than yours?
Can you send the manufacturer and catalog number for your unit? You have my interest even though I don't feel like I can give you much valuable advice at the moment.

Thanks for the interest - this does appear to be a tough nut to crack. The wiring has been verified by both electricians, that can probably be ruled out. I'll ask him to check the grounding electrodes too.

The last ELU that was in (essentially the 2nd replacement unit after the burnout) is a locally produced CBI (Circuit Breaker Ind) QA17C63A. 63A rated. The one that's in now is an upgrade of that one. Both exhibit the same behaviour.