Why Does My Fuse Keep Blowing or My Breaker Keep Tripping?
A fuse that blows immediately or a breaker that trips when the actuator starts is almost always a sign of overcurrent — either a short circuit, an overloaded actuator, or an undersized fuse. Here's how to diagnose and fix it.
Common Causes
| Cause | When It Happens | Next Step |
|---|---|---|
| Fuse too small for actuator | Blows immediately on startup | Replace with correct rating (see table below) |
| Short circuit in wiring | Blows immediately, even with no load | Inspect all wire connections; look for bare wire contact |
| Actuator motor shorted internally | Blows immediately after replacing fuse | Test actuator in isolation; contact PA Support if internal short confirmed |
| Overloaded actuator | Blows during operation under heavy load | Reduce load or upgrade to higher-rated actuator |
| Stall at end of stroke without limit switch | Blows when actuator reaches end | Verify internal limit switches are wired and working |
Correct Fuse Sizing
| Actuator Model | Peak Current | Recommended Fuse |
|---|---|---|
| PA-01, PA-12 (micro/mini) | 2 A | 3 A slow-blow |
| PA-14, PA-04, PA-03, PA-18 | 5 A | 7.5 A slow-blow |
| PA-09, PA-10 | 10 A | 15 A slow-blow |
| PA-17 (industrial) | 20 A |
25 A slow-blow |
⚠️ Always use slow-blow (time-delay) fuses DC motors draw 3–5× their running current at startup (inrush). A fast-blow fuse sized for running current will blow on every startup. Slow-blow fuses tolerate short inrush spikes while protecting against sustained overcurrent.
Testing for a Short Circuit
1. Disconnect the actuator
Remove the actuator from the circuit completely. Replace the fuse and power on the control box — if the fuse blows again with nothing connected, the short is in the control box or wiring, not the actuator.
2. Test actuator resistance
Use a multimeter on resistance mode across the two actuator motor wires. A healthy actuator reads 1–10 Ω (motor winding resistance). A reading near 0 Ω indicates an internal short — the actuator needs replacement.
3. Inspect all wiring
Look for wires with damaged insulation, bare conductors touching, or connectors with pushed-back pins causing shorts between adjacent circuits.