Overload Or Ground Fault Detected On Electrical System

Common Symptoms

• Unit shuts down immediately and displays alarm 00100 on the Display Module
• Red alarm light is lit and unit will not restart in AUTO or MANUAL mode
• Unit trips off when plugged into shore power or switched to electric standby mode
• READY light goes out and STOP condition is active with no cooling output
• Evaporator fans may stop spinning mid-cycle before shutdown
• Cargo temperature rises because refrigeration has been lost
• APX Display Module shows a shutdown alarm that must be manually cleared before the unit can restart

Probable Causes (Ranked by Likelihood)

• Ground fault in the electric standby motor or motor wiring -- insulation breakdown allowing current to flow to the chassis Very Likely
• Overloaded electric standby circuit due to low incoming voltage (brownout) causing excess current draw Very Likely
• Faulty or tripped overload relay on the electric standby contactor Likely
• Damaged or chafed shore-power cable or plug creating a leakage path to ground Likely
• Failed electric standby contactor with welded or arcing contacts Possible
• Water or moisture intrusion into the electric standby junction box or motor terminal block Possible
• APX controller input board fault causing a false ground fault reading Less Likely

Step-by-Step Diagnostic Procedure

1. Do not attempt to reset and restart the unit until you have inspected the shore-power supply. Press STOP on the Display Module, disconnect the shore-power plug from the receptacle, and confirm the unit is de-energized before touching any wiring.

2. Visually inspect the entire shore-power cable from the plug to the junction box on the unit. Look for cut insulation, burn marks, melted plastic, or corrosion on the plug pins. Replace a damaged cable before proceeding.

3. Check incoming shore-power voltage at the receptacle with a multimeter. For a 460 V / 3-phase unit, you need 440-480 V between all three legs. For a 230 V single-phase unit, verify 208-240 V. Low voltage (more than 10 percent below spec) causes excess current draw and will trigger this alarm repeatedly.

4. Locate the electric standby overload relay in the electrical panel on the unit. Check whether the relay has tripped by pressing its manual reset button (small red or yellow button on the relay body). If it trips again immediately on the next start attempt, the overload or ground fault is real and you must keep investigating, not just keep resetting.

5. With the shore-power cable disconnected and all power off, use a multimeter set to the highest resistance (Ohms) range and measure from each power leg at the motor terminal block to the unit chassis ground. You should read open circuit (OL or infinite resistance). Any measurable resistance below 1 megohm indicates a ground fault in the motor windings or wiring.

6. Inspect the electric standby motor terminal box and the contactor panel for water, condensation, or oil contamination. Dry the area with compressed air. If terminals show corrosion or tracking marks (carbon paths), clean with electrical contact cleaner or replace the affected components.

7. If all wiring and the motor check out clean, connect power and monitor the APX Display Module during the standby start sequence. If 00100 returns immediately with no apparent overload cause, the APX input board or current transformer may be faulty. At that point you need a trained reefer technician with Carrier diagnostic software to evaluate the controller.

Frequently Asked Questions