Index of Products

Master Highlights

Starting Methods

There are a variety of starting methods for Fire Pump Controllers, each with a different answer for how much current will be drawn when the motor is initially started. The more the reduction of the inrush current, the more complex the equipment must be.

The links below will discuss in detail each starting method beginning with the most basic, the Across the Line controller, or you may read a brief comparative summary here.

Across the Line
Wye Delta Closed

Part Winding
Soft Starting

Primary Reactor
Autotransformer

Wye-Delta Open
Variable Speed

Part-Winding, Single Source

Inrush Current:
360-420%

Motor Starting Operation:
After receiving a start signal, our model MCP controller energizes the first run contactor to connect half of the motor windings to the line. Once connected, the motor starts accelerating the fire pump. After a time delay (adjustable, factory set at 3 seconds) the transition takes place by energizing the second contactor. When it closes, the remaining motor windings are connected to the line to finish acclerating the fire pump to its normal operating speed.

Motor Starting Current:
Once half of the motor windings are connected to the line, the motor draws 60-70% of its locked rotor current. The actual reduction depends on the specific motor used. As the motor speed increases, the starting current decreases according to the part winding speed-current curve. When transition occurs, the motor current jumps to the across-the-line current at the speed at which transition took place. From here the current quickly reduces its normal running value.

Motor Starting Torque:
When half of the motor windings are energized, the motor produces 50% of its locked rotor torque to begin accelerating the fire pump. As the speed increases, the torque dips slightly until the speed reaches 50% of full speed. At this point, the torque dips further to 35% or less of the rated torque. This is inherent with part winding motor designs, so the actual torque produced at 50% speed should be determined by the motor manufacturer.

Typically, enough torque is produced to accelerate a fire pump past this speed. Once past this speed, the motor's torque builds up rapidly according to the part-winding speed-torque curve. When transition occurs, the motor torque jumps to the across-the-line torque and accelerates the fire pump to its running speed.

It should be noted that a special part winding wound 6 or 12 lead motor is required.