Electric Drill: Trips the Power Source Circuit Breaker

The carbon brushes provide the electrical current to the armature. There are housed inside the brush holders that keep them in place with a spring that allows them to ride on the commutator. If the brushes become damaged, have a heavy build-up of debris, or become worn out, it can impact their ability to provide electricity to the motor, resulting in a short or ground (depending on the issue).

To check the condition of the brushes, separate the two halves of the case by removing the screws. Locate and remove the brush holders by gently pulling on the wire. Check the condition of the brushes for ships, cracks, breakage and anything else out of the ordinary. Measure the brushes – they should not be 1.8 of an inch, or less. If the brushes are too short, replace them. Press down on the brush to check for good spring compression. You can replace the brushes and springs by pressing the tab on the side of the holder. Remove the brush and spring. Clean the holder with electrical contact cleaner and install new brushes and springs. Make sure the tab locks in place on the brush holder during installation. Reinstall back on drill case using a small screwdriver to hold the brush down, giving you clearance. Reassemble the drill case back together.

If you are using an extension cord that is too long and/or not the proper gauge rating for your power tool, it can cause the circuit breaker to trip because of too much resistance in the extension cord. This can cause heat, or also a fire, if the breaker does not trip. The wrong extension cord also puts stress on the power tool, shortening its life. Make sure to use a heavier gauge cord for power tools and try to keep them as short as possible.

The switch turns the power on and off to the motor. To check the switch for a short, or grounding out, causing the circuit breaker to trip, you will have to access the switch. Remove the screws securing the two halves of the case together and open the case. Remove the switch from the drill by disconnecting the wires at the terminals. Remove any hold down brackets, if applicable. If you notice any burn marks, then replace the switch as it has a short or it is grounding out. If the switch looks good, you can verify it by checking it for continuity by attaching a multimeter set to an ohmmeter and each wire on the switch. The switch should read infinity, or zero, in the off position. When pressed, you should get a reading. If you do not get a reading in the on position, then replace the switch. Install the new switch in the housing. Reattach the wires to the correct connection and reattach any hold down brackets. Reassemble the case back together.

The power cord delivers power to the drill from the outlet. Examine the cord for any cracks, splits, cuts, burn marks or anything else out of the ordinary that could cause a short. If you notice any of these, replace the cord. A cord that shorts out can cause the circuit breaker to trip. If the power cord looks good, it may have come loose inside the drill grounding out. Open the cause of the drill by removing the screws securing the two halves of the case. Check the connection where the power cord is connected, to make sure they are attached and tight. If the cord requires replacement, disconnect it from the connection. Remove the cord guard. Install the guard on the new cord. Strip approximately ½ inch of insulation from the new cord, if it has not come that way, and twist the wire. Attach the wires to the appropriate connections inside the drill. Secure the cord in the case. Ensure the guard is in place on the housing when you reassemble the case back together.