Breaker each time i plug in my portable 3.5 horse 20 gallon compressor it throws the breaker in the electric panel it has done this at several locations. What is wrong?

Pneumatic tools are rated in cfm (cubic feet per minute). Your 1 HP air compressor is rated at probably not more than 3 cfm while the 1/2 " impact driver needs at least 8 cfm, maybe 12 chm of air.
The compressor must provide more chm than tool rating needs.
It is a problem, by the time you look at five horse power air compressors and larger, a lot of electric power is needed. A circuit of 220 volts, 20, 30, or more amps would be required to run those large expensive compressors.
If you can, return the air tool and get a good electric tool instead.
Leave those high air volume air tools to shops that are so equipped to use, or invest if you must.

The start capacitor isn't doing it's job

If the in-tank check valve is leaking air back into discharge line from the pump, the motor will not have enough power to overcome headpressure. Easy test with some air in the tank. Remove the discharge hose at the brass check valve at tank. Spray soapy water on valve to test for leak. If leaking remove the valve and clean the seat or replace as needed (drain air from tank before you remove the valve). If no leak at the valve, test the capacitor(should read to within 95% of mfd rating). Good luck

Hi, my name is John. Welcome to FixYa. You may be use to small a breaker, it need to have a 20 amp breaker, next, somebody may have put a smaller gauge wire for the cord,you need to have at least a 12gauge or 10gauge wire. the wire will have it written on it. Thanks for choosing FixYa...John

I have read that a thin or long extension cable can cause this. But you can also circuit breaker that plugs into the line before the device. And I would think the breaker on the main board would be enough protection.

What are you plugging it into? It needs a 20 amp breaker, and no extension cord, and it has to be warm. In cold weather they are sluggish, a cord will drop the amps down quite a bit, if it doesn't have the at least 16 amps on start up , it will pop a breaker. So check this out. hope it helps.

To be honest with you your compressor is what is commonly referred to as a throw away. You can't even imagine how many times I have posted that in the past month for your compressor and similar ones, such as the 3 gallon 1.5 hp craftsman.

The Porter Cable Is more reliable or rather it used to be. I believe that there are so many manufactures around the world pumping these things out that in order to get a reliable compressor you have to do it through the warranty. I know Senco makes a pretty good portable compressor. I believe Home Depot carries it and the cost is around $125.00.

That said your compressor may be salvageable so don't write to Santa just yet.
Almost all compressor,(even the throw a ways), come with a reset switch. The problem is finding it.
If you don't have your manual then start looking. You may need to remove the plastic shroud to locate it. All it is is a small black or red plastic button about a 1/4" in diameter.
Since you stated that there was a power outage that kind of rules out loose wiring or incorrect extension cord size. You may want to check the breaker though. You may have already but check it again. You want to turn it off and on a couple times to see or rather feel if the breaker itself has became compromised.
I hope something here helps.

hi!
there are several factors we can consider it comes from short circuited.if you did not rewire the circuit its fine,but if you rewire the circuit and it happen there is wrong connection it may happen every time you power on,check your connection the common line of the motor should as your L1(line 1) and line2 should connect to line capacitor w/c that is your starting capacitor.the pressure switch should be in series connection with line 1 or on line 2
check also the bearing of your motor if worn out replace bearing,because the worn out bearing develop hi ampere it shorted also the electrical system if there is sticky bearing.check also your capacitor if busted capacitor it will also open your breaker besause it can not start up.hope this can help you.

to long of a cord or to small of Gage wise or filters are clogged or compactor on the motor is going bad.

There is a one way valve that only lets air from compressor to tank. If this isn't working the motor is trying to start under the pressure of the tank, and therefore tripping your breaker.