Based on the information you provided, it seems like the cord connecting the electrical box to the shed might be the cause of the issue. There could be a few potential problems with the cord that could result in the breaker tripping:
Overloading the Circuit: If the microwave and the shed are drawing too much power from the circuit simultaneously, it can exceed the circuit's capacity, causing the breaker to trip. This could happen if the appliances in the shed are running concurrently with the microwave.
Inadequate Wiring or Faulty Cord: The cord itself may be inadequate for carrying the load required by the shed and the microwave. It could be too thin or damaged, leading to electrical resistance, overheating, or even a short circuit, which triggers the breaker to trip for safety reasons.
Ground Fault or Short Circuit: There might be a ground fault or a short circuit occurring within the cord or the wiring within the shed. A ground fault occurs when the live wire comes into contact with the ground wire or a conductive surface, while a short circuit happens when the live wire comes into direct contact with the neutral wire. Both situations can cause excessive current flow, leading to the breaker tripping.
To address the problem, it's crucial to ensure that the electrical system in the shed, including the cord and the wiring, is properly installed and can handle the electrical load required by the shed and the microwave. It's advisable to consult a qualified electrician who can assess the situation, identify any underlying issues, and provide appropriate solutions to resolve the problem safely. Electrical issues can be hazardous, so it's essential to prioritize safety and seek professional assistance when dealing with such matters.