Our tumble dryer trips out after 30 minutes......every time.
What trips? The RCD or the circuit breaker/fuse?
RCD tripping = earth leakage = risk of electric shock.
Circuit Breaker tripping = too much power being consumed = risk of fire.
AIUI most newer wiring has just one RCD protecting the whole house. So any earth leakage anywhere in the house causes the RCD to trip and you loose electricity to everything - plugs, lights, cookers, central heating, emersion heaters the lot.
There can/will be many circuit breakers though. Typically upstairs plugs (ring main), downstairs plugs (ring main), lights, electric cooker, garage, boiler, immersion heater etc. Each of these have their own fuse/circuit breaker. Each of these fuses/circuit breakers will have their own current ratings. If the fuse/circuit breaker trips then it's something wrong with that particular circuit, and not an earth leakage issue.
Ring mains can be problematic. They're typically fused at 30/32A. If you plug 3 devices capable of drawing 13A each and run them at the same time then you probably will trip the CB. So Say you turn the kettle and toaster on, and then someone else puts the tumble dryer on, and all 3 are plugged into the same ring main, then the CB may well trip.