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

Autotransformer, Single Source

Inrush Current:
50% tap = 150%
65% tap = 252%
80% tap = 384%

Motor Starting Operation:
After receiving a start signal, the model MCT controller energizes the start contactor and the wye contactor to connect the autotransformer into the starting curcuit. With the autotransformer in the circuit, the motor voltage is reduced by transformer action thereby reducing the starting current drawn from the line.

Once connected through the autotransformer, the motor starts accelerating the fire pump under reduced voltage conditions. After an adjustable time delay, factory set for 3 seconds, transition takes place by de-energizing the wye contactor and energizing the main contactor.

When the main contactor closes, the autotransformer acts as a reactor when the wye contactor opens, the motor remains connected to the power source through the transition to maintain closed transition operation. When the autotransformer is completedly bypassed, the fire pump accelerates to its normal operating speed.

Motor Starting Current:
Once connected to the line through the 50%, 65%, or 80% autotransformer taps the line current respectively drawn by the motor is 25%, 42%, or 64% of its locked rotor current. As the speed increases, the starting current decreases according to the autotransformer speed-current curve for the taps selected. When transition occurs, the line current jumps to the across-the-line current at the speed at which transition took place. From here, the current quickly reduces according to the across-the-line speed-current curve.

Motor Starting Torque:
When energized through the 50%, 65%, and 80% autotransformer taps, the motor respectively produces 25%, 42%, or 64% locked rotor torque to begin accelerating the fire pump. AS the speed increases, the torque dips slightly before it rapidly increases according to the autotransformer speed-torque curve for the tap selected. When transition occurs, the motor torque jumps to the across-the-line torque and accelerates the fire pump to its running speed.