{"id":8778,"date":"2026-09-23T06:18:48","date_gmt":"2026-09-23T06:18:48","guid":{"rendered":"https:\/\/www.simplybuyglobal.com\/?p=8778"},"modified":"2026-10-13T00:35:56","modified_gmt":"2026-10-13T00:35:56","slug":"soft-starter-vs-star-delta-starter","status":"publish","type":"post","link":"https:\/\/www.simplybuyglobal.com\/fa\/comparison\/soft-starter-vs-star-delta-starter\/","title":{"rendered":"Soft Starter vs Star-Delta Starter: Cost, Current & Torque"},"content":{"rendered":"

Quick answer:<\/h2>\n\n\n\n

A star-delta starter cuts starting current and starting torque to roughly one-third of a direct-on-line start, and none of it is adjustable. A soft starter ramps the voltage instead, so you can set a current limit, keep built-in motor protection and stop the load smoothly – at a higher device price. Choose star-delta for light, low-torque loads; choose a soft starter when the load needs more starting torque, protection or a soft stop. Simply Buy supplies both routes as a multi-brand distributor and supply-chain integrator, with genuine stock and DDP delivery.<\/p>\n\n\n\n

This guide is for B2B distributors, system integrators, EPC buyers and plant maintenance teams choosing a motor starter for a three-phase motor. It answers three buying questions in order: how much starting current each option draws, how much starting torque it leaves you, and what each one really costs to buy, run and maintain. Then it gives you a selection table and the information to send for a quote.<\/p>\n\n\n\n

Scope: low-voltage three-phase induction motors up to 690 V, started at fixed speed. Every motor starter here is a fixed-speed device. Not medium voltage, and not variable-speed drives – when a VFD is the answer, it is usually because you need speed control rather than a gentler start.<\/p>\n\n\n\n

Two terms first. Direct-on-line (DOL) starting means switching the motor straight onto the supply – the cheapest method and the harshest. A contactor is a heavy-duty relay that switches motor current. Compare a soft starter vs star delta starter on price alone and the star-delta starter wins almost every time; our motor starter range<\/a> covers both routes.<\/p>\n\n\n\n

Which Motor Starter Reduces Starting Current, and By How Much?<\/h2>\n\n\n\n

A cage induction motor started direct-on-line typically draws 6 to 8 times its full-load current while it accelerates – a figure stated plainly in Nidec’s engineering guide to soft starters. That surge is why both the star-delta starter and the soft starter exist, and both work the same way: they reduce the voltage the motor winding sees.<\/p>\n\n\n\n

A star-delta starter does it in one fixed step. In the star connection, each winding sees 1\/\u221a3 of the line voltage, about 58%, so winding current falls by the same ratio, and torque – which follows the square of voltage – drops to one third. Because line current in star equals winding current, the current at the terminals lands near one third of a DOL start. On a motor that draws 6 to 8 times In at DOL, that is roughly 2 to 2.7 times In. Low, and free of electronics – but fixed.<\/p>\n\n\n\n

A soft starter spreads the same reduction across a controlled ramp. Schneider Electric’s Altistart 48 (ATS48) lets you set the maximum starting current from 1.5 to 7 times motor In, capped at 5 times the starter’s nominal current, with ramp-up times from 1 to 60 seconds, per the Altistart 48 catalogue. For fans, compressors and crushers, the usual working range is 300% to 450% of full-load current.<\/p>\n\n\n\n

\"Star-delta<\/figure>\n\n\n\n

Internally, they differ: a soft starter uses thyristors – solid-state switches with no moving parts – while a star-delta starter uses three contactors and a timer. What you pay for with a soft starter is control, not extra torque: both motor starter types reduce voltage, and only one lets you choose how much.<\/p>\n\n\n\n

Two Things a Star-Delta Starter Does That a Soft Starter Does Not<\/h3>\n\n\n\n

First, a fixed low current for very light loads. For light, repetitive starting duty, a star-delta starter can hold starting current low and costs less than a soft starter, and the Nidec guide makes that argument directly. Fair – provided you accept the second one.<\/p>\n\n\n\n

Second, the transition. At the star-to-delta changeover, there is a current transient and a torque shock, described in the same guide. That is the moment a star-delta starter loads the motor, the coupling and the driven machine. A soft starter ramps continuously, with no changeover step.<\/p>\n\n\n\n

Why Does Starting Torque Decide More Than Starting Current?<\/h2>\n\n\n\n

Because the load, not the motor starter, sets the limit. Ask one question: can this load reach full speed on one third of the motor’s DOL starting torque?<\/p>\n\n\n\n

Motors declare locked-rotor and starting torque under IEC 60034-12. For a common design-N motor, the figure typically falls between about 1.5 and 2.5 times rated torque, so one third lands near 0.5 to 0.85 times rated torque. Read the datasheet rather than assuming: if it declares 2 times rated torque at DOL, a star-delta starter leaves you about 0.67 times rated torque, and the load either accelerates on that or it does not.<\/p>\n\n\n\n

Loads that start comfortably at low torque:<\/p>\n\n\n\n