Kick-Start and Pedestal Voltage on a Soft Starter Explained

What are kick-start and pedestal voltage on a soft starter? Pedestal voltage — also called initial voltage — is the starting point of the open-loop voltage ramp, typically set 30-50% of line voltage per the ramp profile in IEC 60947-4-2; kick-start (breakaway pulse) is a short boost, often 90-100% of line voltage for roughly 0.1-0.5 s, fired before the ramp to break static friction on a stalled load. Set the pedestal too low and the motor sits at standstill drawing near-locked-rotor current without turning; set it too high and the starter forfeits its inrush-reduction purpose, stressing the SCRs and the driven load close to a direct-on-line start. This article covers what pedestal voltage does to starting torque, which loads need a kick pulse and which must never see one, how both settings interact with current limit and ramp time, typical starting points by load type, and the field symptoms that trace back to a wrong setting.

What Pedestal Voltage Actually Sets

On a voltage-ramp soft starter, pedestal voltage is the SCR firing angle the controller holds for an instant at time zero, before the ramp begins climbing toward full voltage. It is not a torque setting directly — it is a voltage setting, and torque follows from it. The motor produces essentially no useful torque until the applied voltage produces more torque than the load demands at zero speed. Below that threshold, current flows, heat builds, and the rotor does not turn.

A pedestal set at 30% gives roughly 9% of DOL locked-rotor torque (0.3² = 0.09); at 50% it gives 25%. That difference matters on a loaded conveyor or a positive-displacement pump, where breakaway torque can exceed 100% of motor full-load torque. Too low a pedestal on such a load produces a start that never leaves zero rpm — the current limit trips, or the thermal model calls it a stall.

What a Kick-Start Pulse Actually Does

Static friction (stiction) is higher than sliding friction. A gearbox that has sat overnight, a screw conveyor packed with material, or a plunger pump against a closed check valve can need a torque spike just to get the shaft moving, after which the running torque required drops. A kick-start pulse exploits that gap: the starter fires SCRs at a high angle — near full voltage — for a fraction of a second, then drops back to the pedestal and begins the normal ramp. The pulse duration is short enough that thermal stress stays low even though the instantaneous voltage is high.

What we see in the field: kick-start gets left enabled from a previous application and forgotten. On a light, free-spinning fan load it does nothing useful — the load was never stuck — but it does add an unnecessary voltage spike every start. Disable it unless breakaway torque is a genuine, measured problem.

Loads That Need a Kick Pulse — and Loads That Should Never See One

Screw conveyors, positive-displacement pumps against a closed valve, crushers with jammed feed, and some gearmotors with worn bearings are the typical candidates. The common trait: a load that resists the first fraction of a turn more than it resists running. Centrifugal pumps, fans, and most conveyors under normal (unloaded) start conditions do not need it — their torque curve is smooth from zero speed upward, and the fluid or belt is already moving, not stuck.

Using a kick pulse on a load that does not need one is not harmless. It reproduces a slice of DOL inrush every single start, which defeats the reason for installing a soft starter in the first place — reduced electrical and mechanical stress. On pump systems specifically, an unnecessary voltage spike can also reintroduce the pressure transient the soft starter's ramp was chosen to prevent; see our guide on soft starter for pumps for ramp and soft-stop settings tuned to avoid check-valve slam.

Setting Pedestal Voltage and Kick-Start Alongside Current Limit and Ramp Time

These settings do not work in isolation. Current limit (typically 300-400% FLC) caps how much current the SCRs will pass regardless of the voltage the ramp profile is calling for; if the pedestal plus load demand would draw more current than the limit allows, the current-limit function overrides the voltage ramp and holds current flat until speed rises enough to reduce it. Ramp time (typically 5-30 s) sets how long the climb from pedestal to full voltage takes. A short ramp with a low pedestal produces an aggressive, near-step start; a long ramp with a low pedestal can stall entirely if breakaway torque is not met early.

The practical sequence for commissioning: set current limit first, based on the supply's tolerance for start current and the motor's thermal withstand. Then find the minimum pedestal that reliably breaks the load away — raise it in small steps from a low starting value rather than guessing high. Only then add a kick pulse if the motor still hesitates at the new pedestal. Read this alongside our breakdown of voltage ramp, current ramp, and torque control methods, since torque-control units handle this whole sequence in a closed loop instead of open-loop voltage steps.

Why Torque-Control Units Change the Picture

On torque-control soft starters (ABB PSTX, Schneider Altistart ATS480, Siemens 3RW55), the controller measures motor current and estimates torque directly, then adjusts firing angle in real time to hold a linear speed rise rather than a linear voltage rise. Pedestal voltage and kick-start still exist as parameters, but the closed loop compensates for load variation automatically — a torque-control unit is far less likely to stall on a load with an unpredictable breakaway spike than a plain voltage-ramp unit set once and left alone. For background on how the SCR firing itself works across both control types, see how a soft starter works.

Typical Starting Points by Load Type

Pumps (centrifugal)

Pedestal 30-40%, no kick pulse, ramp 10-20 s. Centrifugal pump torque rises with speed squared, so a low pedestal is normally sufficient and a smooth ramp avoids water hammer on the discharge side.

Conveyors (belt, loaded at start)

Pedestal 40-50%, kick pulse only if the belt is loaded and stationary at start, ramp 10-20 s. A belt conveyor started empty rarely needs a kick pulse; the same conveyor started full of material sometimes does.

Fans and blowers

Pedestal 30-40%, no kick pulse, ramp 10-30 s. Fan torque also rises with speed squared and inertia is the dominant sizing concern, not breakaway.

Crushers and screw conveyors

Pedestal 40-50%, kick pulse frequently enabled, ramp 5-15 s. These are the loads most likely to need the pulse — packed or jammed material resists the first fraction of a turn.

These are starting points for commissioning, not fixed values — the correct setting always depends on the specific load's breakaway torque and inertia, which datasheet values alone rarely capture. What we see in the field: the same conveyor model needs different pedestal settings depending on whether it is loaded or empty at start, so the commissioning technician has to test both conditions, not just one.

Field Symptoms of a Wrong Setting

A pedestal set too low shows up as a motor that hums at standstill, then trips on stall protection or current-limit timeout without ever reaching full speed — the ramp is climbing, but too slowly relative to the load's resistance at zero rpm. A pedestal set too high, or a kick pulse enabled on a load that does not need it, shows up as an audible mechanical jolt at start and, over time, premature wear on couplings, belts, or gearbox components — essentially a miniature DOL start hidden inside a soft-start commissioning record. Not always obvious from the trip log alone.

Nuisance stalls are frequently blamed on the motor or the starter's current-limit setting when the real cause is an under-set pedestal. Before increasing current limit or swapping components, check whether the load's breakaway torque exceeds what the pedestal voltage can deliver.

These settings also sit inside a broader protection and sizing picture — phase loss, stall timers, and thermal models all interact with how the ramp begins. For the full sizing process, see sizing a soft starter for a motor, and for how these parameters are documented against duty ratings, see the IEC and UL standards for soft starters. Our soft starter selection guide covers how pedestal and kick-start settings fit alongside the rest of the commissioning checklist, and our full range of soft starters spans economy voltage-ramp units through torque-control models where this tuning is largely automatic.

Conclusion

Pedestal voltage sets how much starting torque a soft starter delivers at zero speed, and because torque falls with the square of voltage, small pedestal changes produce large torque swings. Kick-start exists for one narrow purpose — breaking static friction on a load that resists the first instant of rotation — and should stay disabled everywhere else. Commission both settings against the load's actual breakaway behavior, not a copied value from a different application, and current limit plus ramp time will do the rest of the work correctly.