Fire Pump Controller Starting Methods: Full vs. Reduced Voltage

Electric fire pump controller starting methods fall into two groups. Full-voltage (across-the-line) starting connects the motor to line voltage in one step. Reduced-voltage starting uses part winding, an autotransformer, a wye-delta connection, or a solid-state soft starter to cut the inrush current drawn from the utility or generator. The trade-off is lower starting torque.

Eaton builds each method into a specific controller series, so the model number tells you how the controller starts the motor. FD models have no built-in transfer switch, and FT models add an integrated automatic transfer switch. This guide covers how each method works, what Eaton lists for its starting current and torque, and what drives the choice.

Why Do Fire Pump Controllers Use Different Starting Methods?

Reduced-voltage starting exists to limit inrush current. When a large motor starts across-the-line, it draws a short, heavy surge from the power source. That surge can pull down supply voltage and strain a utility service or standby generator that also carries other loads.

Each reduced-voltage method cuts that surge in a different way. Every one of them also reduces the torque available to accelerate the pump. The right method balances the power supply's limits against what the motor and pump need to come up to speed.

How Do the Starting Methods Compare?

The table below shows the figures Eaton publishes for its EPCT Fire electric controllers. Reduced-voltage values are shown relative to across-the-line starting, which Eaton lists at 600% starting current and 100% starting torque.

Source: Eaton EPCT Fire product brochure, 2018

Eaton has also offered primary-resistor starting (FD50 and FT50), and it now lists the FT50 as discontinued. If you maintain an older controller with a 50-series model number, identify it by its nameplate before you source parts.

How Does Across-the-Line Starting Work?

An across-the-line controller applies full line voltage to the motor through a single contactor. It's the simplest method and delivers full starting torque right away. It also draws the highest inrush current of any method.

Eaton's FD30 and FT30 use this method. Per Eaton's ratings, they cover motors up to 400 HP at 440–480 V. Across-the-line starting suits sites where the service and transformer can absorb the full inrush without unacceptable voltage dip, and where the utility doesn't restrict starting current.

Limited-service controllers such as the FD20 and FT20 also start at full voltage. They're intended for smaller motors, 30 HP or less, where the authority having jurisdiction accepts them. Browse FD20 limited-service fire pump controllers for these models.

How Does Part Winding Starting Work?

A part-winding controller energizes one set of the motor's windings first, then brings the second set online after a short delay. The motor starts in two steps instead of one, which lowers the initial current demand.

Eaton lists part-winding starting at 65% of across-the-line current with 50% starting torque. The motor has to be designed for part-winding starting, with six connections between controller and motor. Eaton offers it as the FD40 and FT40. At 440–480 V, these are rated for motors up to 600 HP.

How Does Autotransformer Starting Work?

An autotransformer controller places an autotransformer in the motor's supply circuit. This lowers the voltage at the motor terminals during acceleration and produces a smooth start. Once the motor is up to speed, the controller switches to full voltage.

Eaton lists autotransformer starting at 45% of across-the-line current and 42% starting torque, using a standard three-connection motor. That combination of meaningful inrush reduction without a special motor winding is why sites with constrained power often consider it. Eaton offers it as the FD60 and FT60. See our FD60 autotransformer fire pump controllers.

What Is the Difference Between Open and Closed Transition Wye-Delta?

Both versions start the motor with its windings connected in a wye configuration, then reconnect them in delta to run. Eaton lists both at 33% of across-the-line starting current and 33% starting torque. The difference is what happens during the switch from wye to delta.

• Open transition (FD70 / FT70): the motor is briefly disconnected from the supply while the windings are reconfigured, then reconnected in delta. That reconnection can cause a second current surge.
• Closed transition (FD80 / FT80): the motor stays connected to the supply during the changeover, which avoids the break in power and the reconnection surge.

Both versions need a motor wound for wye-delta starting, with six connections. At 440–480 V, Eaton rates these controllers for motors up to 600 HP. Whether a site needs closed transition depends on how sensitive the power source is to that transition surge, which is a call for the engineer of record.

How Does a Soft Start Fire Pump Controller Work?

A soft start controller uses a solid-state starter instead of stepped contactor sequences. Eaton describes the FD90 as providing a smooth, stepless current ramp to the motor. That ramp avoids current surges and mechanical torque transients.

Eaton also notes a soft stop feature that decelerates the motor gradually. According to Eaton's FD90 product page, this is intended to eliminate water hammer through the full start-stop cycle. Starting current and torque are adjustable rather than fixed, and a standard three-connection motor is used. Eaton offers soft start as the FD90 and FT90.

How Do You Choose a Fire Pump Controller Starting Method?

The starting method is a design decision that belongs to the project's engineer of record, made under NFPA 20 and the local authority having jurisdiction. These factors usually drive it:

• Power source capacity: how much inrush the utility service, transformer, or standby generator can absorb without excessive voltage dip.
• Utility limits: whether the utility restricts motor starting current.
• Motor design: part winding and wye-delta need motors built for six connections. Across-the-line, autotransformer, and soft start use three.
• Torque needs: whether the pump can reach speed with the reduced torque of a given method.
• Hydraulic behavior: whether pressure surges in the piping are a concern, which points toward soft start.
• Transfer switch: whether an alternate power source calls for an FT model with an integrated transfer switch.

This guide doesn't cover motor sizing, wiring, or installation. Use Eaton's documentation and the project's engineer of record for those decisions.

Fire Pump Controller Starting Methods FAQs

What are the starting methods for a fire pump controller?

Electric fire pump controllers start the motor either at full voltage or at reduced voltage. Full-voltage methods are across-the-line and limited service. Reduced-voltage methods include part winding, autotransformer, wye-delta open transition, wye-delta closed transition, and soft start. Eaton assigns each method its own series, from FD20 and FT20 through FD90 and FT90, so the model number identifies the method.

What is the difference between full-voltage and reduced-voltage starting?

Full-voltage starting applies line voltage to the motor in one step. That gives full starting torque but also the highest inrush current; Eaton lists 600% starting current for across-the-line controllers. Reduced-voltage starting lowers that inrush to protect the power source, at the cost of less starting torque. Which one fits depends on the supply, the motor, and the pump.

Which starting method has the lowest inrush current?

Among Eaton's fixed-value methods, wye-delta starting has the lowest published figures: 33% of across-the-line starting current and 33% torque, for both open and closed transition. Soft start is adjustable rather than fixed, so its starting current is set to suit the application. The right choice still depends on whether the pump can accelerate on the reduced torque.

Does part winding or wye-delta starting need a special motor?

Yes. Eaton lists six motor connections for part-winding and wye-delta controllers, so the motor has to be designed for that starting method. Across-the-line, autotransformer, and soft start controllers use a standard three-connection motor. Confirm the motor's design with the pump and motor manufacturer before specifying a controller.

Can you change the starting method on an existing controller?

The starting method is part of the controller's design, which is why each method has its own FD or FT series. Changing methods generally means a different controller, a check of the motor's connections, and review by the engineer of record and the authority having jurisdiction. For replacement parts on an existing controller, match parts to its current series and nameplate.

Find the Right Eaton Controller or Replacement Parts

Browse our full range of Eaton fire pump controllers, from limited-service and across-the-line models to part winding, autotransformer, wye-delta, and soft start, with or without a transfer switch. For a controller already in service, shop Eaton fire pump controller replacement parts by controller series.

For quote-driven controllers or help matching a series to your project, call (786) 336-5783 or send your project details through our contact form.