Author(s): Jeff Sargent. Published on May 1, 2013.

Neither Snow, Nor Rain, Nor Heat
Protecting the emergency power supply, no matter what’s thrown at it

NFPA Journal®, May/June 2013 

Shortly after Hurricane Sandy struck the East Coast last fall, I began a series of columns on emergency power supply systems (EPSS) to raise awareness of the relevant requirements in several NFPA codes and standards. My primary point in the series — this is the third and final installment — is that following those requirements during the design, installation, and operation of the system can help ensure that power continues, regardless of the cause of interruption to the main power supply.



March - April 2013
NFPA 110 provides performance requirements for emergency systems

January - February 2013
A feature of any emergency power system is a standby power source

November - December 2012
A proposal for 2014 NEC fine-tunes the requirements for clear work space

September - October 2012
The 2014 NEC considers electrical design for people with disabilities

July - August 2012
Part II of a review of proposed articles for the 2014 edition of the NEC®

May - June 2012
A closer look at a new proposal for the 2014 National Electrical Code

When commercial power is interrupted, standby electrical systems are relied upon to provide power until the utility source is restored. The location of the emergency power source is an important factor in assuring its ability to function under adverse conditions. Although a grade or sub-grade-level location most likely won’t be affected by many of the events that can result in power interruption, such as thunderstorms or utility pole damage due to an automobile accident, the impact of a catastrophic natural disaster or other event must also be considered. NEC Section 700.12 specifies that “equipment shall be designed and located so as to minimize the hazards that might cause complete failure due to flooding, fires, icing, and vandalism.” NFPA 110, Emergency and Standby Power Systems, provides a similar requirement covering the location of the emergency power supply (EPS) in subsection 7.1.2.

These requirements direct designers of emergency power supply systems to consider the types of natural disasters that a geographic location may experience when locating the EPS and supporting equipment. NEC and NFPA 110 requirements can be met by using such established benchmarks as the 100-year floodplain; elevating a generator to protect it from flooding, for example, will do little good if the fuel supply and associated pumps are located at grade. Similarly, NFPA 110 contains provisions for lightning protection for EPSs installed outdoors and on rooftops, and for designing the EPS and associated equipment to withstand anticipated shocks in recognized seismic areas.

Where the EPS is located indoors, NFPA 110, Section 7.2 requires a separate room that must provide an envelope with a two-hour fire-resistance rating. The only other equipment permitted in the room is other emergency power supply system equipment. Requirements for prohibited types of fire protection (suppression) systems in the EPS room are specified in subsection 7.11.2.

Another key component in ensuring EPS operation when utility power is lost is to implement the routine maintenance and operational testing requirements in Chapter 8 of NFPA 110. General testing and maintenance requirements are also found in NEC Section 700.3. NFPA 110, subsection 8.4.2 requires monthly operational tests of diesel-powered generator sets for not less than 30 minutes and specifies minimum levels of performance. Spark-ignited generator sets (natural gas or gasoline) are also required to be tested monthly for 30 minutes under the conditions in paragraph In addition to the monthly testing of the EPS, Chapter 8 also contains prescriptive requirements for operation testing of transfer switches and other emergency power supply system equipment.

Every 36 months, a Level 1 system is required to be tested for the duration of its assigned operating class (i.e., its minimum required operational time), or for four hours, whichever is less.

These are the kinds of requirements that can help ensure that emergency power supply systems work whenever they are called upon. As Hurricane Sandy and countless other events, both natural and man-made, have shown us, the stakes are too high to take chances with emergency power.

Jeffrey Sargent is a regional electrical code specialist for NFPA.