Fire pump systems are among the most critical life safety loads in any facility. Because these systems must operate during fires, utility outages, and other abnormal conditions, the National Electrical Code treats fire pump power differently than nearly any other electrical load. NEC 695.7 specifically addresses voltage drop, with the goal of ensuring fire pumps start and run reliably when they are needed most.
For electrical engineers and experienced contractors, understanding how NEC 695.7 applies to emergency and backup power systems is essential to delivering compliant and dependable installations.
Why Voltage Drop Is a Bigger Issue for Fire Pumps
Fire pump motors draw very high inrush current during starting. If the voltage at the fire pump controller drops too far during this event, the motor may not accelerate properly or may fail to reach full speed. In a fire scenario, this can directly impact water pressure and system effectiveness.
Unlike normal loads, fire pumps are expected to tolerate some level of voltage reduction. However, NEC 695.7 regulates voltage drop for fire pump circuits to ensure reliable operation. It requires that voltage at the controller line terminals does not drop by more than 15% during motor starting, and voltage at the motor terminals does not drop more than 5% when running at 115% of full-load current.
This is especially important when fire pumps are supplied by emergency or standby generators, where voltage dip during motor starting is more pronounced than with a utility source.
What NEC 695.7 Is Trying to Ensure
NEC 695.7 is designed to confirm that sufficient voltage is available at the fire pump controller under both normal and emergency power conditions. The code recognizes that fire pumps must be able to start across the line and continue running, even when power quality is less than ideal.
Key intent of NEC 695.7 includes:
- Maintaining adequate voltage at the fire pump controller line terminals
- Accounting for motor starting conditions, not just steady operation
- Ensuring emergency generators can support fire pump starting without excessive voltage drop
- Preventing undersized conductors and equipment that could compromise performance during an emergency
This requirement goes beyond the typical voltage drop guidance used for lighting, receptacles, and other non life safety loads.
Emergency Generators and Fire Pump Performance
Emergency and backup generators play a central role in many fire pump installations. In many facilities, the generator is the only source of power during a fire related utility outage. Because of this, generator selection and system design must be evaluated carefully with NEC 695.7 in mind.
Important generator related considerations include:
Generator sizing
Generators must be sized not only for running load, but also for the high starting current of the fire pump motor. Undersized generators can experience excessive voltage dip during starting, even if they appear adequate for other emergency loads.
Voltage dip and recovery
Fire pump motors demand immediate torque. The generator must maintain sufficient voltage during the starting event and recover quickly to support continuous operation.
System impedance
Transformers, switchgear, and long feeder runs all contribute to voltage drop. When combined with generator source impedance, these factors can significantly reduce available voltage at the fire pump controller.
Coordination with other emergency loads
Fire pumps are typically given priority over other emergency loads. Proper sequencing and load management are critical to maintaining compliance and system reliability.
Common Challenges in Generator Fed Fire Pump Systems
Some of the most frequent issues encountered in the field include:
- Assuming a generator suitable for general emergency power is adequate for fire pump starting
- Failing to evaluate voltage drop under generator operation
- Long conductor runs that increase voltage drop beyond allowable limits
- Retrofit projects where existing generators were not originally designed to serve fire pumps
These challenges often surface late in the project, during testing or inspection, which can lead to costly redesigns or equipment changes.
Designing for Compliance and Reliability
Meeting NEC 695.7 requires coordination between electrical design, equipment selection, and installation practices. Voltage drop calculations, generator performance analysis, and conductor sizing all need to be addressed early in the project, especially when emergency generators are involved.
Global Power Supply supports electrical engineers and contractors on projects where fire pump reliability and code compliance are critical. Extensive experience with emergency generators, backup power systems, and complex electrical infrastructure allows code requirements to be addressed proactively rather than reactively. Experienced power system engineers assist with evaluating generator performance, voltage drop, and overall system design for demanding applications.
For projects involving fire pumps, emergency generators, and life safety systems, proven experience navigating codes and regulations helps ensure systems operate reliably when failure is not an option.