Here's why:

* Electrical Code Violations: Electrical codes are designed for safety. Replacing a lower-amp breaker with a higher one violates these codes and can lead to serious consequences.

* Overheating and Fire Hazards: A 30-amp breaker is designed to handle more current than a 20-amp breaker. If your toaster and microwave draw a combined current exceeding 20 amps, the 30-amp breaker might not trip, allowing excessive current to flow through the wiring. This can overheat the wires and lead to a fire.

* Wire Gauge: The wire gauge in your circuit is matched to the breaker size. A 30-amp breaker requires thicker wiring than a 20-amp breaker. Using a 30-amp breaker with the existing wiring can cause overheating.

* Appliance Safety: Toasters and microwaves are typically designed to operate on circuits protected by 15-amp or 20-amp breakers. Using a higher-amp breaker could damage these appliances.

What to do instead:

* Identify the Problem: First, determine why your 20-amp breaker is tripping. It could be a faulty toaster or microwave, a wiring issue, or simply that the two appliances are drawing too much power simultaneously.

* Consult an Electrician: If you suspect a wiring problem or are unsure how to diagnose the issue, it's crucial to consult a qualified electrician. They can identify the root cause and recommend the safest solution.

* Reduce Load: Consider using only one appliance at a time or plugging them into separate circuits if possible.

* Replace Faulty Appliances: If an appliance is faulty, replace it with a new one.

Remember: Electrical work should always be performed by a qualified electrician. Attempting to fix electrical problems yourself can be dangerous.