Soft starter faulting or not ramping the motor
A soft starter won't ramp the motor up smoothly — it faults out, the motor jerks or doesn't reach full speed, or the bypass doesn't engage.
Safety first
Soft starters control high motor currents through power semiconductors. Isolate and prove dead before working on power terminals. The motor can start when the fault clears.
Isolate, lock out / tag out, and prove dead before working unless a live test is specifically required, authorised, and carried out under proper supervision. Always follow local regulations, your site procedures, and the equipment manufacturer's documentation.
Apprentice mode
Full walk-through — the why, what readings mean, mistakes & safety.
Likely causes
Ranked from most to least likely.
- 1
Incorrect ramp / current-limit settings
Most likelyRamp time or current limit set wrong for the load causes faults or a motor that won't get up to speed.
- 2
Missing start command / enable
#2The start signal or enable isn't reaching the starter, so it won't begin the ramp.
- 3
Bypass contactor not engaging
#3After ramp-up the bypass should take over; if it doesn't close, the starter may overheat or fault.
- 4
Motor or load problem (overload during ramp)
#4A jam or heavy load during the ramp draws excess current and faults the starter.
- 5
Faulty power semiconductor (SCR/thyristor)
Least likelyA failed power device in the starter causes uneven ramping or hard faults.
Reports are saved on this device to reflect what you actually find.
Testing sequence
Work through one test at a time. Expected reading and what each result means.
On the tools? Job Mode shows one test at a time with thumb-sized buttons — your place and readings carry straight over.
Enter Job ModeRead the exact fault/status on the starter and note when it faults (on command, during ramp, at bypass).
A clear fault code and a repeatable point of failure.
The pattern points to the cause group — proceed accordingly.
If random, suspect intermittent wiring or a marginal power device.
View all expected readings at once
Fault-finding flowchart
The same logic as a decision tree.
- 1start
Soft starter faulting
→ step 2 - 2decision
Does it fault before the ramp even begins?
Yes→ step 3No→ step 4 - 3result
Check start/enable command and basic settings.
- 4decision
Does it ramp but fail at/around bypass changeover?
Yes→ step 5No→ step 6 - 5result
Bypass contactor not engaging — check the bypass circuit.
- 6decision
Is the motor/load within rating during the ramp?
Yes→ step 7No→ step 8 - 7result
Suspect a power semiconductor — refer to starter documentation.
- 8result
Overloaded ramp — review the load / ramp settings.
Common mistakes apprentices make
- Cranking the ramp too short and then chasing the resulting faults.
- Not realising the bypass contactor should take over after ramp-up.
- Blaming the starter when the driven load is overloaded during start.
- Resetting repeatedly into a hard power-device fault.
When to stop & escalate
Suspected failed power semiconductors or repeating hard faults should go to the manufacturer's documentation/support with the exact code. A genuinely overloaded start should be reviewed mechanically.
If you're past your competence, authorisation, or the safe limits of the job — stop and hand it on. There's no fault worth getting hurt over.
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Related faults
VSD powered up but won't start the motor
The drive is energised and the display is alive, but it won't run the motor. No fault may be shown — it just sits in 'ready' or 'stopped' and ignores the start command.
Motor overload keeps tripping
The thermal/electronic overload trips repeatedly, either on start or after the motor has run for a while. Resetting only buys you a short run before it trips again.
VSD trips on overcurrent / overload
The drive trips with an overcurrent or overload code — on start, on acceleration, or under running load. It may restart and trip again on the same point in the cycle.
Learn the theory
How the gear and circuits behind this fault actually work.