What Causes Air Compressors to Trip Immediately After Startup?

I. First, Clarify: Normal Startup Current Logic to Avoid Misjudgment

II. 6 Core Causes: Detailed Analysis from Easiest to Most Difficult

1. Abnormal Power Supply Voltage (Most Easily Overlooked, Accounting for 25%)

• Low or unstable voltage: During factory peak electricity usage, excessively thin wire gauge (e.g., 4mm² copper wire for a 22kW motor, insufficient cross-section), or overloaded transformers can cause the motor terminal voltage to be lower than the rated value at startup (actual voltage ≤340V for a 380V motor). Low voltage results in insufficient motor starting torque, leading to a sharp increase in current and tripping.
• Judgment method: Use a multimeter to measure the voltage at the motor input terminal. The no-load voltage should be within 380V±5%, and if the voltage drop exceeds 10% at startup (e.g., dropping below 340V), it is a voltage issue.
• Solutions: Avoid starting during peak electricity usage; replace with thicker wires (6mm² copper wire is recommended for 22kW motors); install a voltage stabilizer to stabilize voltage; for three-phase power, check for phase loss (voltage of one phase is 0) and tighten terminal connections.

2. Electrical System Faults (Most Common, Accounting for 30%)

• Loose or oxidized wiring: Motor terminals and electrical control box terminals may loosen due to vibration or oxidize after long-term use, increasing contact resistance. Local heating at startup triggers protective tripping.
  • Judgment: After powering off, open the electrical control box. If terminals are blackened, have burn marks, or can be shaken by pulling lightly, they are loose.
  • Solutions: Tighten all terminals with a screwdriver; polish severely oxidized contacts with sandpaper or replace terminals.
• Motor faults (short circuit/grounding): Damage to motor winding insulation causes interphase short circuits, or winding grounding (insulation resistance ≤2MΩ). A short-circuit current forms instantly at startup, directly triggering the circuit breaker to trip.
  • Judgment: Use a megohmmeter to measure motor insulation resistance. If it is 0 or much lower than 2MΩ, or the motor housing is live (grounding resistance ≤4Ω is normal), it is a motor fault.
  • Solutions: Slight insulation damage can be repaired by drying; severe short circuits require professional rewinding of windings; for grounding faults, inspect the contact point between windings and the housing and repair insulation.
• Improper selection or failure of protective components: The rated current of the circuit breaker (air switch) is less than the motor’s starting current requirement (e.g., a 10A air switch for a 7.5kW motor with a rated current of 15A), or the thermal relay’s setting current is too low. Aging of protective components or failure of the tripping mechanism can also cause false tripping.
  • Judgment: Check the nameplate of protective components. The circuit breaker’s rated current should be 1.2-1.5 times the motor’s rated current, and the thermal relay’s setting current should match the motor’s rated current.
  • Solutions: Replace with matching circuit breakers or thermal relays; directly replace aging components.

3. Mechanical Load Jamming (Accounting for 20%)

• Main engine jamming: Wear of screw rotor, aging and seizing of bearings, or blockage of rotor gaps by carbon deposits and sludge prevent the motor from rotating at startup, causing a surge in load current and tripping.
  • Judgment: After powering off, manually rotate the motor fan or main engine coupling. If it is stuck, cannot rotate, or has excessive resistance, the main engine is jammed.
  • Solutions: For minor jamming, inject a small amount of lubricating oil and attempt to rotate; for severe cases, disassemble and inspect the main engine, clean carbon deposits, or replace rotors and bearings (performed by professionals).
• Belt-driven model faults: Overly tight belts (deflection ≤1cm) increase motor starting load, or misaligned/seized belt pulleys; severe belt slipping causes the motor to idle without driving the main engine, leading to motor overload and tripping.
  • Judgment: Observe if the belt is tight or worn; check if the belt pulley rotates smoothly manually.
  • Solutions: Adjust belt tension (deflection 1-2cm), replace slipping or damaged belts, and align belt pulleys.
• Bearing seizure: Wear or lack of lubrication in motor or main engine bearings causes seizure, preventing the motor from rotating at startup and forming “locked-rotor current” that triggers tripping.
  • Judgment: If the motor shaft cannot be rotated manually and the bearing end cover is overheated, it is a bearing fault.
  • Solutions: Replace with bearings of the same model and add grease; avoid mixing different types of grease.

4. Improper Startup Method (Accounting for 10%)

• Star-delta starter faults: Failures of contactors or time relays in the star-delta starter prevent switching to star connection at startup (direct delta connection causes excessive current), or ablation/adhesion of contacts during switching.
  • Judgment: Frequent contactor clicking sounds at startup, or no switching action followed by immediate tripping.
  • Solutions: Check if starter contacts are ablated and if time relay parameters are correct (general startup time 3-5 seconds); replace contactors or time relays if damaged.
• Incorrect inverter parameters (for variable-frequency models): Excessively short acceleration time (≤5 seconds), excessively low starting frequency (≤10Hz), or excessively low overload current setting in variable-frequency air compressors causes excessive current shock at startup and tripping.
  • Judgment: The inverter displays “overload” or “overcurrent” alarms.
  • Solutions: Access inverter parameters, set acceleration time to 8-15 seconds, starting frequency to 15-20Hz, and overload current to 1.1-1.2 times the motor’s rated current.

5. Control Circuit Faults (Accounting for 8%)

• Controller (PLC) or relay faults: After the controller sends a startup command, it fails to properly control contactor closure, or relay contacts are ablated/adhered, leading to abnormal circuit tripping.
  • Judgment: No contactor clicking sound in the electrical control box at startup, or abnormal controller indicator lights (e.g., not lit, flashing).
  • Solutions: Restart the controller to restore default parameters; check if relay wiring is loose and replace ablated relays; contact manufacturer after-sales for complex controller faults.
• Emergency stop button or limit switch faults: Unreset emergency stop buttons, adhered contacts, or unclosed limit switches (e.g., door control switches) cause control circuit open circuits, triggering protective tripping at startup.
  • Judgment: Check if the emergency stop button is popped up, equipment doors are closed tightly, and limit switches are in the closed state.
  • Solutions: Reset the emergency stop button; repair or replace faulty limit switches.

6. Other Hidden Issues (Accounting for 7%)

• Earth leakage tripping: Damage to motor insulation, water ingress, or moisture in the electrical control box causes leakage current to exceed the limit at startup, triggering the earth leakage protector to trip.
  • Judgment: The compressor starts normally after replacing with a regular circuit breaker, or trips immediately after resetting the earth leakage protector.
  • Solutions: Inspect motor insulation, dry moisture in the electrical control box, repair damaged wires, and avoid equipment moisture.
• Environmental factors: Low room temperature (≤5℃) increases lubricating oil viscosity, increasing motor starting load; or motor moisture, excessive dust blocking heat sinks, causing poor heat dissipation at startup and triggering overheating tripping.
  • Judgment: Prone to occur in winter or humid environments, with condensation or dust accumulation on the motor housing.
  • Solutions: Raise the room temperature to above 10℃, clean motor heat sinks, and dry damp components.

III. Three-Step Troubleshooting: Efficiently Locate Problems

1. Step 1: Quick Check of Electrical Basics (10 minutes)Measure power supply voltage (three-phase balance and whether it is low), tighten terminals, check if the emergency stop button and limit switches are reset, and manually rotate the motor fan to check for smooth operation.
2. Step 2: Targeted Inspection of Core Components (30 minutes)Use a megohmmeter to measure motor insulation resistance, check if protective components are properly selected, verify star-delta starter or inverter parameters, and disassemble to inspect belts or couplings for jamming.
3. Step 3: Professional Maintenance for Complex FaultsIf the above steps are ineffective, the fault is likely due to main engine jamming, motor short circuit, or controller failure. Contact the brand’s after-sales service for disassembly and inspection to avoid secondary damage from blind disassembly.

Summary