Soft Starters
A soft starter ramps a motor up to full speed gradually by controlling voltage at start-up, cutting inrush current and mechanical shock compared to a direct-on-line start. NLS sources soft starters to IEC 60947-4-2, sized to the motor's voltage, full-load current, and starting torque, for pumps, fans, and compressors where a hard start isn't acceptable.
A soft starter sits between the supply and the motor and reduces the voltage applied at start-up, then ramps it back up to full voltage over a set time, instead of slamming the motor straight onto full line voltage the way a direct-on-line starter does. The result is a start that draws maybe two to four times full-load current instead of the six to eight times a direct-on-line start pulls, and a motor shaft that spins up smoothly instead of jerking a pump, fan, or belt drive under sudden torque.
NLS sources soft starters built to IEC 60947-4-2, the standard covering AC semiconductor motor controllers and starters, which sets the performance and test requirements for thyristor-based ramp control. Units get selected against the motor's rated voltage, full-load current, and starting torque demand rather than picked as a generic size, since an undersized soft starter overheats on a hard-starting load like a positive-displacement pump, and an oversized one adds cost without adding benefit. Bypass contactors are standard on most units above a certain frame size, cutting heat loss once the motor reaches full speed.
On Saudi projects, soft starters show up on pumps and compressors where a hard start would cause water hammer or belt slip, on large fan drives where inrush current would trip an undersized supply, and anywhere a facility's electrical infrastructure can't absorb a direct-on-line start's current spike without affecting other equipment on the same feed. They're a lower-cost alternative to a full VFD where a project only needs a soft start, not continuous speed control after the motor's up and running.
NLS quotes soft starters against the motor's nameplate data, voltage, full-load current, and starting torque, and confirms whether bypass contacts and communication options are required before pricing, returning a quote in USD. Standard panel-mount units in common current ratings typically source within a few weeks; larger frame sizes or units built into a custom enclosure run on a manufacturer-confirmed lead time.
Specifications
- ✓Standard: IEC 60947-4-2 (AC semiconductor motor controllers and starters)
- ✓Control method: thyristor-based voltage ramp at start and stop
- ✓Starting current reduction: typically 2 to 4x full-load current, vs 6 to 8x direct-on-line
- ✓Sizing basis: motor rated voltage, full-load current, and starting torque
- ✓Bypass contactor: standard on most frame sizes above entry level
- ✓Options: communication interfaces and soft-stop for pump applications
Frequently Asked Questions
What's the difference between a soft starter and a VFD?+
A soft starter ramps voltage at start and stop only, then runs the motor at full speed on line power. A VFD controls speed continuously throughout operation. NLS quotes a soft starter where a project just needs a gentle start, not ongoing speed control.
Why would a project use a soft starter instead of direct-on-line starting?+
To cut the current spike and mechanical shock of a direct start. Direct-on-line starting can pull six to eight times full-load current and jolt a pump or belt drive; a soft starter reduces both, protecting equipment and the supply.
Does NLS size soft starters for pumps specifically, to avoid water hammer?+
Yes. For pump applications, NLS confirms whether a soft-stop function is needed alongside the soft start, since a pump stopped too abruptly can cause water hammer in the same way a hard start does.