Over a few years the GFI (1st photo below) has been tripping randomly. There was a real case many years ago when it tripped for a reason and was due to a leaky seal in a water pump in our outdoor fish pond. New pump fixed it.

However, over time it would trip with no obvious reason at 5mA. Changed to the next level after looking at the house electrics and was ok for a while and started again. Upped it again but now had to set it to off position but still trips a few times a week. Seems random as it can happen with very little running except normal appliances or heavy loads where it gets worse.

I'm guessing that it is the GFI that is failing as I can find nothing in the house to account for it. The outdoor electrics have all been disconnected for some time now.

Went looking for a replacement at Home Pro but found them to be pricier than I thought - see photo 2.

Guess my question is, do GFIs begin to deteriorate over time? 2nd, is that price (nearly 4000 baht) reasonable?

It would appear you have a breaker overload rather than GFI if trips when turned off. As unit is only rated 30 amps and seems to be feeding a panel with 95 amp breakers (and no apparent main breaker to trip) expect you need a larger unit. As for the 5mA setting that is probably too low for most if any motor/compressor type equipment involved as there is always a bit of leaking as they age.

My Safe-T-Cut which still serves main panel was bought in 1977 and works fine. As I recall price even then was over $100 (after exchange rate) so 4k now would seem reasonable (price down but inflation up).

It would appear you have a breaker overload rather than GFI if trips when turned off.

Was thinking that may be the case but it seems to happen even with light loads (normal appliances), same loads as when it wasn't having this problem. Though I have seen breakers start failing over time and perhaps it is the breaker part and not the GFI circuit.

I've seen Safe-T-Cut recommended before so will go looking at another store. The name "Powur-Cut" doesn't feel right.

If you have everything running through that 30 amp breaker can understand trips. That is not enough for most people as master breaker (normal 15 amp meter service will usually have a 65 amp main breaker).

Just an update on this. I bought a new GFI a couple of weeks ago but didn't get around to replacing the faulty one. Last night after about a dozen trips figured it was time since Saturday is a day off.

Took the old one apart and as you can see from the photo below why it was getting hot on the mains high side including the box and wire. Pitted/corroded contact causing a resistive junction and as such the source of the heat. 2nd picture of what I installed - 50 amps and 1700 Baht.