I have a Square D electrical box. I need to know if I can run my 30 amp dryer off of a 20 amp breaker.
No the dryer is two large of a load for a 20 amp. Code requires the size for calculations at 5000w, this would require a double pole 30 amp breaker to be properly sized. Number 10 wire from the breaker to the outlet.
This really is as simple as 30 being bigger than 20. No, this will not work. A 20 amp circuit can only handle appliances up to 20 amps.