Eaton Eaton Power Circuit Breaker MDN-416 MDN-416

Pre-inspection conditions: Device(Fixed): Position of Poles: Open, Mechanism: Discharged, Device Position in Cassette: -. Device(Drawout): Position of Poles: Open, Mechanism: Discharged, Device Position in Cassette: Removed.

When a circuit breaker experiences a high-level fault or during regularly scheduled maintenance periods, the circuit breaker’s arc chutes and arc chambers should be inspected for any kind of damage or dirt. Be especially alert for signs of significant erosion of the V-shaped plated inside the arc chute.

Arc chutes fit inside the arc chambers and down over the primary contacts. Each arc chute is held in place by either 1 (SB) or 4 (SBSE) top inserted screws.

Remove arc chute screws and all arc chutes from the arc chamber.

Turn each arc chute upside down and visually inspect the inside.

Look for erosion and sooty discoloration on the splitter plates and insulating jacket If arc chutes show severe signs of erosion or discoloration, replace with a new arc chute.

Note: Because the arc chutes are removed, this is an ideal time to inspect the primary contacts for wear (See Primary Contact Inspection procedure on page 59).

When the inspections are complete, position each arc chute over its respective set of primary contacts, and secure in place with the screw(s) removed earlier Be sure to torque arc chute screws to 35 to 45 in-lb.

Sign off on the arc chute inspection

Device (Fixed): Position of Poles: Open, Mechanism: Discharged, Device Position in Cassette: -.

Device (Drawout): Position of Poles: Open, Mechanism: Discharged, Device Position in Cassette: Removed.

For Magnum Breakers with Vertically Mounted Primary Disconnects:

1. With breaker removed from cell, verify that vertical adapter nuts and bolts are torqued to 37–43 lb-ft.

For All Magnum Breakers Primary Disconnects:

1. Remove the primary disconnect.

Warning: Breaker accessory voltages can vary within the same breaker. Be sure to review the accessory voltage rating before energizing as damage may occur.

This test procedure assumes that the breaker is equipped with optional shunt trip (ST), undervoltage release (UVR), and/or spring release (SR) accessories (Figure 94). If one accessory is missing, substitute the manual button or manual charge handle to replace the accessory’s function. If equipped with a motor operator, the voltage is listed on the breaker nameplate.

Charge the breaker mechanism springs using the motor operator

Is the breaker equipped with a UVR?

If equipped with a UVR, energize the UVR with the rated voltage.

Close the breaker by applying rated voltage to the spring release accessory and verify closing by noting the state of the indicating flag.

Charge the breaker mechanism springs using the motor operator. If using the motor operator, after charging, remove power to the motor operator to prevent automatic recharging.

Open the breaker by applying rated voltage to the shunt trip accessory.

Pre-inspection conditions: Device (Fixed): Position of Poles: Open, Mechanism: Discharged, Device Position in Cassette: -. Device (Drawout): Position of Poles: Open, Mechanism: Discharged, Device Position in Cassette: Removed.

Note: Using the mating line of the housing halves as a reference guide will assist in this visual inspection.

Remove the arc chutes, look directly down into the arc chamber (Figure 98), and visually inspect each primary contact structure for signs of wear and/or damage.

Use the contact wear indicator to inspect each contact The contact wear indicator is the relative position of the individual contact fingers to a narrow, side-to-side ledge inside the arc chamber The ledge is actually part of the arc chamber When the circuit breaker is closed and the contacts are in good condition, the narrow ledge is covered by the back end of each of the contact fingers (Figure 99) If the back end of any of the contacts are below the ledge, the contact assembly should be replaced.

Once the inspection is complete, be sure to verify the arc chutes are properly replaced as previously described in the Arc Chute Inspection procedure.

WARNING: ARC CHUTES MUST BE SECURED PROPERLY IN PLACE BEFORE A CIRCUIT BREAKER IS INSTALLED IN A CIRCUIT BREAKER COMPARTMENT. FAILURE TO DO THIS COULD RESULT IN EQUIPMENT DAMAGE, BODILY INJURY, OR EVEN DEATH.

Device (Fixed): Position of Poles: Open, Mechanism: Discharged, Device Position in Cassette: -.

Device (Drawout): Position of Poles: Open, Mechanism: Discharged, Device Position in Cassette: Removed.

2. With breaker removed from cell, verify that the breaker secondary disconnect pins are fully seated and locked into position by lightly pulling on each wire individually.

Note: Do not exceed 1 lb of force or damage to pin or housing may occur.

3. Ensure all pins are straight without bends, corrosion, or show evidence of arcing.