Why Do Voltage Sags Cause Entire Robot Lines to Shut Down? Power Supply Quality and Reset Troubleshooting for Multi-Brand Control Cabinets

If ABB, FANUC, KUKA, or YASKAWA robots on a production line shut down collectively during the startup of high-power equipment, thunderstorms, or grid switching, the fault cause may not lie with the robot body itself, but rather with short-term fluctuations in the control cabinet's input power supply. After voltage recovery, the equipment can sometimes restart, which can easily lead to a misjudgment of "sporadic alarms."

01. First, Confirm if the Shutdowns Share a Common Time Point
Retrieve the robot alarm history and synchronize it with the event logs of the PLC, frequency converter, welding machine, air compressor, and power distribution system. If multiple devices experience controller reboots, communication interruptions, or servo power loss within the same minute or even the same moment, priority should be given to checking the common power supply and network infrastructure. Alarm text varies across brands; maintenance personnel should focus on the occurrence time, power loss sequence, and affected scope, rather than replacing modules based solely on alarm names.

02. Distinguish Between Voltage Sags and Internal Control Cabinet Faults
After performing power-off, voltage verification, and discharge confirmation, check for looseness, overheating, or discoloration at the incoming line terminals, circuit breakers, contactors, transformers, and power module connections. If only a single robot is abnormal, continue checking that device's branch circuit, internal cabinet power supply, and connectors; if multiple devices are abnormal simultaneously, then test the upstream power distribution. Ordinary multimeters may not capture very short-duration fluctuations; use appropriate power quality recording equipment to retain trends when necessary. Tightening terminals while energized is prohibited.

03. Investigate Instantaneous Impact from Peripheral Loads
Welding machines, heating equipment, high-power motors, and frequently starting/stopping variable frequency loads may affect the same power supply branch during operation. Compare robot shutdown times with peripheral equipment start/stop records, and check power distribution capacity, line voltage drop, and load distribution. Do not maintain operation by arbitrarily increasing protection device ratings or disabling undervoltage protection, as this increases electrical and equipment risks.

04. Check Grounding, Shielding, and Communication Recovery
After power supply fluctuations, if fieldbus disconnections, encoder communication abnormalities, or I/O status loss occur, also check protective grounding, shield layer connections, switch power supplies, and remote I/O power supplies. After confirming connectors are free from contamination, oxidation, and mechanical looseness, reset according to the equipment manufacturer's procedures. If zero points, programs, or system parameters are abnormal, verify backups first; do not directly overwrite current data.

05. Post-Repair Verification and Preventive Maintenance
After completing industrial robot repair, perform staged power-up, manual low-speed operation, automatic no-load cycling, and load observation to confirm alarms do not recur, while recording input power supply, cabinet temperature rise, and fault times. The robot maintenance plan can include terminal thermal imaging checks, filter cleaning, power distribution inspections, log backups, and power quality spot checks. For recurring sag events, a root cause closure should be completed jointly by robot, electrical, and facility personnel.

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