I agree it's not clearIt's the mcb that won't stay on isn't it, not the rcd from how I'm reading op?
Correct.It's the mcb that won't stay on isn't it, not the rcd from how I'm reading op?
Nope, The RCD isnt tripping, the lights are not even linked to an RCD from what I can tell.maybe reiterate what happens ? that the RCD does indeed trip taking out other appliances when you try to switch the lighting circuit back on.
if (tomorrow) you turn off all the cicruits , does the lighting circuit alone then work ?
so as Bigboy suggested you may have another circuit that is leaking charge into the lighting circuit when it is switched on as well,
so turn the others on and off individually until you find it.
my suspect, like I mentioned might be the one with the UPS - if you have now permanently turned off the immersion switch it can't be that.
as you say, it all sounds weird that you have done nothing to reconfigure the appliance connections in the house and the problem has started unprovoked, maybe when you had turned of ups circuit earlier it started having a problem
I agree it's not clear