Lang ECO-8M Convection Oven

When the main breaker trips it indicates current is escaping from the circuit to ground.
If it is a micro-circuit breaker that trips it indicates the circuit is consuming too much current - a short circuit.

Either way the wiring or the oven elements have a fault and need attention.

In the power panel on your house. There are two circuit breakers with their handles joined.One of these breakers has tripped internally which will stop the heating elements but not the control panel or oven light since they work on 120 volts. Reset the breaker or replace it.

It is possible there is a heavy short on the oven and so the circuit breaker cuts off the supply when the oven is switched ON.
You will need to disconnect the coils to the ovens one by one till it is confirmed of the shorted coils. A test of the coil also will indicate the fault. If this is a ELCB then the ground leak within the oven /poor ground connection of the outlet can also cause the issue. make sure there is no damping in the connections of the power to leak and trip the circuit.

If you were using the oven at the time it is likely that a short circuit occurred in the element causing the circuit breaker to trip. After switching it back on the oven wont work. You probably need to replace the element.
The switch may have tripped for another reason. If it did when you turned the power back on the electronic clock/timer generally reverts to the auto. function. You need to set the clock/timer back to manual so that the oven will work.

HI, Sounds like your from the UK
If you are referring to a trip switch as being equivalent to an American circuit breaker. (Electrical safety device designed to shut down power to an electrical appliance). Then we are on the same page.
Do the following diagnostic procedure:
1 SHUT DOWN THE POWER SUPPLY TO THE OVEN. I.E. THE TRIP SWITCH/CIRCUIT BREAKER.
2 Open the oven door and look very carefully with a flashlight at the heating element. Look at the the entire element. If it blew (similar to when a light bulb blows) you will
find white powder around the hole in it or it will be completely broken, or have bubbles in it. Some indication like that. If so it has failed and must be replaced. It is probably tripping the switch because it is shorting out somewhere. There is also the possibility that the internal wiring connectors to where the element is mounted into the oven walls is broken off and short circuiting against the oven chassis (walls). That being the case, it may be just a wiring repair in which you install new appropriate electrical contacts and re-connect the element.
Hope this helps,
Happy New Year,
Mark

http://www.fixya.com/support/r4964670-get_manual_most_any_electronic_device

You will need to get an ammeter to see how many amps are being drawn by the motor. You can purchase an inexpensive meter at home depot or Radio Shack, The meter should be clamped around one of the wires from the motor. If the amps are more than the internal breaker, the motor is bad (even a new motor) if the amps are lower than the internal breaker, the breaker itself is your problem. You should also verify that you have the proper voltage motor and input to oven. Hope this helps

Check for correct voltage at plug, in the mean time the oven will be disconnected from any power, see if it resets with no power for 10 minutes

thats a direct short somewhere within the oven. it happens whenoyu turn the oven on???, def check for a shorted wire, wire hitting hte cabinet of unit.