40A MCB will trip, but 63A won't: Is this logic even logical?

[Tom.G]

It makes a lot more sense to connect them to appliances that are most likely to electrocute someone, ...than to use them on expensive things. They aren't intended to protect the things, they are meant to protect you.

Well, even hammers have more than one use.

The combination appeared to disconnect everything from an over-voltage condition.
That puts it in the SUCCESS bucket for me.

Remember that the surge protectors often have a fuse in series so that when/if the snubber fails shorted they don't go up in smoke or start a fire.

If you have any protected outlet strips with a pilot light on the surge protector indicating they are functional, see how many of them are still on. (often a Red LED)

Of the four here that are connected directly to the line, one has failed; that's not a particular problem because it is a 'convenience use'; all it is used for is a couple of fans and occassionally a vacuum cleaner.

Cheers,
Tom

 

[Guineafowl]

Based on the stories you told before I can imagine that. Proper working of sensitive devices are hanging on the code supporting them, and without that code they are - well: sensitive.
The question is, whether you chose to adopt the code or the mess.
I think you are trying to go for (a) code.

Pretty much what I was going to say - we’ve had whole-circuit earth fault protection for decades in Europe. An RCD is bound to ‘nuisance’ trip if the wrong type is slapped into a rat’s nest of wires. The arcing light switch tripping is not something I’ve seen. You’d need some badly arc-ed terminals to get that. But then, where’s the fault - RCD or switch?

Getting back to the OP - the max earth fault loop impedance (Zs) for a 40A ‘C’ type MCB is 0.49 ohm at 25 degC. That’s pretty low, and will need some very beefy wires to achieve on a TN earth system, pretty much impossible on a TT system. Please be careful.

To protect the installation (not user), you could spec a 100 mA trip level, and/or use a time-delay version, for example, to get around the problem above. A 100 mA trip level will bump your maximum Zs to 500 ohm, assuming a max touch voltage of 50 V.

I appreciate you’re in tricky circumstances, but I’d say the closer you can get to proper, the better.