Customers running TECO VFDs (TECO VFD series such as JNI, K, etc.) most often ask one thing: "what does the code on the screen mean?" We ranked the high-frequency alarms by how often they show up, and paired each with on-site troubleshooting steps you can follow directly. Bookmark this page—next time a fault pops up, don't rush to call service; you can clear more than half of them yourself.
| Code | Meaning | Most Common Cause |
|---|---|---|
| OC | Over Current | Heavy load, motor short, accel time too short |
| OU / OV | Over Voltage | Decel too fast, inertial load regen, brake resistor missing |
| LU | Under Voltage | Low input voltage, loose wiring, momentary power loss |
| OH | Inverter Over Heat | Fan stopped, heatsink clogged, high ambient temp |
| OL | Motor Over Load | Mechanical jam, wrong rated current set, undersized VFD |
| GF | Ground Fault | Motor/cable insulation damaged, damp-environment leakage |
Don't reset yet. First measure the 3-phase motor current with a clamp meter and check balance; a deviation over 5% usually means insulation aging or a winding short. Second, check whether a contactor was mistakenly added on the output side (frequent switching triggers surge). Third, extend the acceleration time or raise the low-frequency torque compensation. If OC persists, disconnect the motor leads and measure insulation resistance—three-phase balance is normal.
Usually appears when decel is too fast or a heavy-inertia load feeds energy back. Fix: extend decel time to ~1.5× the factory value; add a brake resistor; confirm DC-bus voltage stays under the limit (e.g. T4 class ~750V). If the grid is unstable, add an ACL input reactor.
Check that 3-phase input voltage is not below 10% of rated, terminals are tight, and there is no momentary dropout. With insufficient supply capacity, match the VFD and front-end breaker properly to avoid DC-bus undervoltage trips.
Clean the heatsink dust, check the fan, confirm cabinet temperature. Only re-power after it cools down. In hot workshops, derate or add a separate air duct. TECO VFD alarm reset: after clearing the cause, press Reset on the panel or re-power; if it repeats, don't force-reset—inspect load and supply.
OL: verify motor nameplate current vs VFD rated current, then check for mechanical jam. GF: megger the motor ground insulation; below 0.5MΩ means replace the cable or motor—especially in damp sites.
When commissioning goes wrong, a TECO VFD factory reset saves time: enter the parameter menu and execute the "INIT / initialize" item (exact key path varies by model—see the manual). TECO VFD parameter setting core: first enter motor nameplate data (power, voltage, current, rpm) and run autotune, then set the overload curve by load type (ND for fan/pump, HD for constant torque). Unsure? Ask your distributor engineer for a model-specific parameter sheet.
Q: How do I clear an "Err" display?
A: "Err" is generic—read which one (OC/OU/LU…), fix per the steps above, then reset. If it keeps returning, it's a hardware or load issue needing on-site inspection.
Q: What carrier frequency should I set?
A: Factory environments: 2.5–5kHz. Lower = more stable, less EMI; higher = quieter but hotter. Don't raise it for long heavy loads in high heat.
Q: Are faults worse in summer?
A: Yes. Heat is the #1 enemy of VFDs; with poor cooling, OC/OH alarms can double. Clean dust regularly and keep ventilation.