AdvancedMedium risk

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.

Start fault-finding

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.

Full detail — causes, the why, and common mistakes.

Likely causes

Ranked from most to least likely.

1
Incorrect ramp / current-limit settings
Most likely
Ramp 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
#2
The start signal or enable isn't reaching the starter, so it won't begin the ramp.
3
Bypass contactor not engaging
#3
After 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)
#4
A jam or heavy load during the ramp draws excess current and faults the starter.
5
Faulty power semiconductor (SCR/thyristor)
Least likely
A failed power device in the starter causes uneven ramping or hard faults.

Reports are saved on this device to reflect what you actually find.

Premium fault tree

The full ranked causes, test sequence and flowchart for this fault are part of Sparkie Sidekick Pro.

Coming soon — no payment required during preview.

Testing sequence

Work through one test at a time. Expected reading and what each result means.

Test 1 of 3

Read the exact fault/status on the starter and note when it faults (on command, during ramp, at bypass).

Expected reading

A clear fault code and a repeatable point of failure.

Your actual reading

If it passes

The pattern points to the cause group — proceed accordingly.

If it fails

If random, suspect intermittent wiring or a marginal power device.

Often leads toVSD powered up but won't start the motor Motor overload keeps tripping

View all expected readings at once

1. Read 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.

2. Confirm the start command/enable arrives and check the ramp/current-limit settings against the load.

Valid start/enable and settings suited to the load.

3. Verify the bypass contactor engages after ramp, and check the motor/load for overload during the ramp.

Bypass closes cleanly; motor reaches speed without excess current.

Full test sequence

The step-by-step test flow with expected readings for this fault is part of Sparkie Sidekick Pro.

Coming soon — no payment required during preview.

Fault-finding flowchart

The same logic as a decision tree.

1
start
Soft starter faulting
→ step 2
2
decision
Does it fault before the ramp even begins?
Yes→ step 3No→ step 4
3
result
Check start/enable command and basic settings.
4
decision
Does it ramp but fail at/around bypass changeover?
Yes→ step 5No→ step 6
5
result
Bypass contactor not engaging — check the bypass circuit.
6
decision
Is the motor/load within rating during the ramp?
Yes→ step 7No→ step 8
7
result
Suspect a power semiconductor — refer to starter documentation.
8
result
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.

Related faults

VSDs

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.

5 causes4 test steps

QualifiedMedium risk

Motors & overloads

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.

5 causes4 test steps

QualifiedHigh risk

VSDs Premium

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.

5 causes4 test steps

AdvancedHigh risk

Learn the theory

How the gear and circuits behind this fault actually work.

Device

Soft starter

Reduces motor starting current by ramping the voltage up, then often hands over to a bypass contactor.