My condenser tumble dryer keeps tripping the main 80A switch on my CU.

It runs fine (on half heat setting) for about 40 mins, then trips.

The socket in use is in the garage approx 5 mtrs direct spur to the CU in
the garage on a 16A circuit breaker which does not trip.

Nothing in the house except the fridge/freezer on the kitchen circuit is on
(apart from Sky box on standby) no electric shower etc.

Any ideas?

TIA
--
Vass