Switching off bathroom light will cause ELCB to trip also switching off lighting MCB will cause ELCB trip. There is an extractor fan in bathroom which can be isolated, it still trips if isolator is off or on. Removing feed from light switch to extractor fan has no effect also removing lamp from bathroom fitting still does not prevent trip. No other light switch does this. The board is split with lighting on none ELCB side. Any help in resolving matter would be appreciated John