Milwaukee abrasive cutt-off saw trips breaker when trigger switch is activated. Tried another recepticle and same result. Started while making some 3/8" rebar cuts, made 2 cuts before it started.

If your Milwaukee 6390 circular saw is tripping the circuit breaker even without an extension cord, it could be due to a few reasons:

1. Overloaded circuit: The circuit may be overloaded with too many other electrical devices or appliances. Try unplugging other devices or turning off lights on the same circuit to see if that resolves the issue.
2. Short circuit: A short circuit can occur when the insulation on the electrical wires inside the saw becomes damaged or frayed, causing them to come into contact with each other. This can cause a sudden increase in current flow, which can trip the circuit breaker. Check the saw's power cord for any visible damage or wear, and consider having it professionally inspected if you suspect a short circuit.
3. Faulty circuit breaker: It's possible that the circuit breaker itself is faulty or worn out. Try plugging the saw into a different circuit and see if it still trips the breaker. If it does, the issue may be with the saw itself.
4. Motor overload: If the saw's motor is under strain or is overloaded, it can trip the circuit breaker. Check the blade for any binding or resistance, and ensure that the blade is sharp and properly aligned.

If none of these solutions resolve the issue, you may want to consider taking the saw to a professional repair shop to have it inspected and repaired.

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You wired it incorrectly. If it didn't trip before, and now it does? recheck the way you wired it. Most power tools have a single throw double pole switch. It seems like you have wired Active to Neutral at the switch to cause an immediate power trip.

Scott,
What is the serial number on your saw? I need that to make sure I get the correct info for you.

Quite possible that you have worn out the circuit breaker with multiple trips. Try another circuit that is on a different breaker.

Look around the housing where the switch handle bolts on. You should see a spindle lock pin. With the unit unplugged you want to push in the pin and when you go to tighten or loosen the blade bolt the spindle will lock into place. Sometimes you need to turn the spindle a bit for the lock to catch. Once you have changed the blade just release the pin as it is spring loaded.

If it trips the breaker as soon as you hit the switch, check the power circuit. Check the power cord for frays or cuts, especially where the cord goes into the saw. Remove/split the handle and check the wires into and out of the switch and to the brushes and field. Lood for burned or melted wires or case parts. Milwaukee is notorious for running lots of small wires in very tight places. Make sure none of them got pinched when the tool was assembled. Watch for this also when you reassemble the saw. Check the brushes, if they're worn or broke they can cause a short on the armature. If these all check out you need to have the armature checked on a growler for shorts.
If the saw runs for a few seconds then trips the breaker I'd check for gear and bearing problems. Cehck for free, smooth movement of the bearings on the armature and blade drive assembly. The blade should turn freely by hand. Feel for undue resistance or a gritty feel in the bearings and gears. If necessary replace any offending parts.

when things start overheating componants start to break down. sounds like you need to check the armature and field for burnt areas. at least change the brushes. were you bearing down hard? sounds like the motor may not be enough to cut quickly, maybe more slowly. hope this helps