Fire pump controllers follow rules foreign to other types of controllers.
When starting and running a fire pump, reliability is paramount. How do you obtain that reliability with an electrically driven pump? Let's look at some of the differences between industrial motor controllers and electric fire pump controllers.
Industrial motor controllers use the philosophy of "no start, no run" unless every sensor and interlock is "permissive." Standards focus on the safety of people and equipment. Anomalies like broken wires, shorts, and ground faults prevent a start or run. Overload relays protect running motors from overheating and prevent damage from re-starts. Controllers listed to UL508 standards default to a "no start, no run" mode.
When it comes to fire pump controllers, none of this is true. In the event of fire, you must start and run that pump. NFPA 20 considers conductors and some equipment supplying power to the fire pump motor sacrificial in favor of starting and running. If possible, we expect the fire pump controller to default to a nuisance "start and run"; regardless of anomalies. If you work with fire pump controllers, you need NFPA 20.
Let's look at some of its principles:
• External circuit failure (open or short circuit) can't prevent pump operation. Breakage, disconnecting, shorting, etc., can cause continuous running but can't prevent the controller from starting the pump due to causes other than these external circuits.
• No "remote stop" buttons.
• Overcurrent-sensors must be non-thermal type.
• Protective devices must not have memory affecting reset time.
• You can't incorporate undervoltage, phase-loss, or other sensors to prohibit motor contactor actuation.
• External devices give your pump automatic starts only by opening a normally closed contact.
• The controller must have an emergency-run handle or lever that mechanically closes.
• You can't use the fire pump controller as a junction box for other equipment.
All fire pump controllers are specifically listed, approved, and labeled for use in fire suppression. Manufacturers design controllers for various starting schemes. Where the Authority Having Jurisdiction (AHJ) judges the power supply to be unreliable, you must provide the controller with a combination or separate upstream automatic transfer switch. These switches provide alternate power upon sensing predefined normal power anomalies. One way they do so is by transferring to a second utility feed or an on-site power production facility. Another way is by starting a diesel generator for on-site standby power.
Schneider is a consulting engineer, formerly with Joslyn Clark Controls, LLB in Lancaster, S.C.