June 2010
For regulatory authorities in the electrical inspection community.
Alternate Power Source
System Codes
Emergency, standby, legally required systems and a fire pump too…
The application requirements for today’s alternate power sources are still largely dependent
upon engine driven generator systems.
Installations can be single or multiple installed
in a parallel configuration determined by load
requirements and critical system needs.
These are problems designers face and
choices to make when developing an
alternate power source system for a structure.
Proper generator selection is not as simple
as selecting the low bid price. In fact, it can
involve the application of numerous codes
and standards. As an example, Section
2701 of the 2009 International Building Code
(IBC) states that required emergency and
standby power systems are to be installed in
accordance with the NFPA 110 and NFPA 111
standards. In addition, Section 2702.1.1 of
the IBC requires that emergency and standby
stationary generators be listed in accordance
with UL 2200, the Standard for Safety of
Stationary Engine Generator Assemblies. UL
White Book category FTSR covers Stationary
Generators Listed to UL 2200. These generators are rated 600 V or less and are intended
for installation and use in accordance with:
• NFPA 70 “National Electrical Code”
• NFPA 37 “Standard for the Installation
and Use of Stationary Combustion
Engines and Gas Turbines”
• NFPA 99 “Standard for Health
Care Facilities”
• NFPA 110 “Standard for Emergency
and Standby Power Systems”
The need for any UL 2200 Listed generator
serving as an alternate power source begins
with the simple decision of which systems need
power when a utility company goes off line.
This is determined using Article 220 of
the 2008 National Electrical Code (NEC)
and a precise load calculation to establish
the actual building load the generator
must supply as required by NEC Sections
695.3(B)(1), 700.5, 701.6 and 702.5. Again,
numerous codes and standards must be
applied to an installation, based on building
occupancy, use, and content loading. States
and municipalities typically adopt the numerous
codes and standards that must be considered
for proper installation such as:
• Building Code
• Life Safety Code
• Health Care Standard (for Medical Facilities)
(continued)
UL
Electrical Connections
a supplement of The Code Authority®
June 2010
Alternate Power Source System Codes (continued)
• Fire Code
• Sprinkler Code
• Fire Pump Code
• National Electrical Code
What is unique about installing emergency
and standby power systems is that often
codes applicable to an installation, will
reference and require the use of a second,
third, or even a fourth code or standard.
The combination of codes and standards
determines the entire set of requirements for
a proper installation of a specific generator
system and its unique components and
features. These codes and standards may
have separate requirements, but they are all
intended to work in harmony and impact the
overall decision to make a code compliant
installation. Here is a basic example:
A building under design is required by Section
903 of the IBC to have a sprinkler protection
system installed in accordance with NFPA
13, the Standard for Sprinkler Systems.
The municipal water system supplying the
building has inadequate pressure to make the
sprinkler system design feasible. A fire pump
is designed into the system as an acceptable water supply source to increase water
pressure for the sprinklers. The designer
specifies a fire pump that complies with NFPA
20, the Standard for Fire Pumps and required
by NFPA 13 and Section 913 of the IBC. The
fire pump now becomes part of the design
requirement for the required sprinkler system.
This UL 2200 Listed generator will
supply three individual UL Listed
transfer switches evaluated to
UL 1008, Standard for Safety of
Published by the Regulatory Services
Department of Underwriters Laboratories Inc.
© 2010. All rights reserved.
Transfer Switch Equipment, to provide backup
power to critical circuits. Additional information
on transfer switches may be located in the UL
White Book under categories:
• WPTZ — Transfer Switches
• WPWR — Automatic Transfer Switches
for use in Emergency Systems
• XNVE — Transfer Switches for use in
Fire Pump Motor Circuits
The fire pump disconnect must be a
supervised connection as required by Section
695.4 of the NEC and clearly marked in
at least one inch letters — as “Fire Pump
Disconnecting Means,” with overcurrent
protection that can carry locked rotor current
indefinitely, and located some distance away
to assure adequate physical separation
from the other disconnects in accordance
with NEC Sections 695.4(B)(1), (2), (3), (5),
695.6(C) and NFPA 20. From this supervised
switch, feeder conductors are sized to 125
percent of the full load current of a fire pump
motor, pressure maintenance pump plus 100
percent of any other associated equipment if
supplied by this feeder per the requirements
of NEC Section 695.6(C)(1). This application
complies with both NEC Articles 695 and
700. The use of a vertical switchboard with
separate sections is not permitted in a single
generator installation due to the requirements
of the NEC Sections 695.4(A) and (B)(2).
Generator selection and sizing is only one of
the many factors that designer’s face. NFPA
20 and NEC Section 695.7 include
requirements that the voltage at
controller line terminals shall not
drop more than 15 percent below
normal (controller-rated voltage)
under motor-starting conditions, and
the voltage at the motor terminals
shall not drop more than 5 percent
below the voltage rating of the
motor when it is operating at
115 percent of the full-load
current rating of the motor. This
requires careful load calculation and generator sizing to
accommodate all loads that must
Managing Editor: Jeffrey A. Fecteau
+1.651.408.8562
Jeffrey.Fecteau@us.ul.com
www.ul.com/tcaec
be served, and the fire pump started with no
dip in voltage. If this proves problematic, load
shedding on start up to eliminate voltage drop
at the controller terminals becomes mandatory. Emergency and legally required standby
generator systems must have a witness
and load test prior to issuing a certificate
of occupancy for a building as required by
NEC Sections 700.4(A), (E) and 701.5(A), (E).
The witness and load test are required to
ensure that a generator listed to UL 2200
is properly sized and installed to carry all
required loads. In addition to the previously
mentioned requirements, NEC Section 695.10
requires fire pump equipment must be listed;
additional information is located in the UL
White Book under categories:
• QXZF — Fire Pump Motors
• QYZS — Fire Pump Controllers
• QVUT — Pumping Equipment for
Fire Service
As the example illustrates, designers often face
complex issues when designing power supply
systems for fire pumps. Often what seems
like a common sense approach may not be
truly code compliant. Careful consideration of
the above-mentioned codes and standards is
essential to a code compliant design and to
receive the approval of the code authorities
from all the interested disciplines.
For more information about UL Listed
generators or UL Listed transfer switches,
please contact Donnie Shields at
+1.847.224.2760 or Donald.Shields@us.ul.com