If the VCB is not tripping, check the following three key points.
UVL and UVM generally use the same electrical diagram for the trip circuit (A5–A6). UVH is similar, but may include One Pulse Controller (OPC).
The contact shown at the top of the diagram corresponds to the Close/Trip switch lever on the control panel door. 52a Contact is Normally Open (NO) auxiliary contact that indicates breaker status (ON/OFF). When the protection relay energizes the trip circuit, the trip signal is sent to energize the trip coil, causing the breaker to trip.
Note: Circuit diagrams are based on the VCB being in the Closed (ON) state with the spring charged.
1. AMP female Pin Connector
Check for voltage at the A5 and A6 pins of the AMP connector when a trip command is issued. Confirm that the trip circuit (Harness wire - Truck Ass'y) is energized.
2.TC1, TC2 or OPC (UVH only) Output
Disconnect the trip coil connection and send a remote trip command. Then measure the voltage at the TC1, TC2 pins or at the OPC output pins (for UVH models). Under normal conditions, voltage should appear momentarily when the trip signal is issued. Before performing this step, ensure that the AMP female connector is functioning properly.
Note: The One Pulse Controller (OPC), when installed, prevents continuous energization of the coil and protects it from burning or damage. Most UVH breakers are equipped with an OPC, although it may be optional depending on customer specifications, and some units may not have it installed.
| 73873173232 | CONTROLLER ASS'Y,AC48,DC48~60V,ONE PULSE PM,VH |
| 73873173233 | CONTROLLER ASS'Y,AC/DC100~130V,ONE PULSE PM,VH |
| 73873173234 | CONTROLLER ASS'Y,AC/DC200~250V,ONE PULSE PM,VH |
3. Trip Coil Check (Resistance/Visual)
First, perform a visual inspection of the trip coil to check for any signs of damage, such as burn marks. If no visible damage is found, measure the coil resistance. If the resistance reading is 0 Ω or OL (open circuit), the coil is likely burned or failed and should be replaced.
Note: For UVH models, the trip coil and close coil share the same specification and item code.
| 80573172246 | PACKING ASS'Y,COIL,AC/DC 110/125V,VH(77113143002) |
| 80573172247 | PACKING ASS'Y,COIL,AC/DC 220V,VH(77113143003) |
| 80573172248 | PACKING ASS'Y,COIL,AC/DC 48V,VH(77113143009) |
Possible findings and root cause can be determined based on voltage presence in the trip circuit. If voltage is present but the breaker does not trip, the likely causes are a burned trip coil or a failed One Pulse Controller (OPC) in UVH models. In this case, the affected components should be replaced.
If no voltage is present, the most likely causes are a protection relay issue or a control wiring issue within the switchgear. A recommended check is to swap in a known-good breaker to determine whether the issue follows the breaker or remains with the panel. If the replacement breaker exhibits the same issue, the problem is likely related to the protection relay or switchgear control panel.
After replacing any failed components, perform final verification by confirming proper trip coil operation, verifying that the breaker trips correctly via a remote trip signal, and ensuring that normal breaker operation has been fully restored.
