The problem could be a water leak within the shower casing or a loose wiring connection. To check for a water leak, make sure you isolate / turn off your electricity supply before removing the shower casing. You may be lucky and find the problem within the casing of either a water leak or a loose electrical connection. Obviously water within the casing is a clear indication of water leakage.
Just a note of caution, a trip switch operates for many reasons. One of them indicating a faulty appliance. This appears to be the case and you shouldn't use the appliance until it has been checked out by a qualified electrician or service engineer. Water and electricity are a very dangerous combination.