COPS: Critical Operating Power Systems
Part 3 of a 3-Part Series
By : Bhavesh Patel
Director, Marketing
Volume 1, Issue 5
The last of a three-part series on Critical
Operating Power Systems (COPS). This
ASCO report describes transfer switch code
requirements when deployed in a data center
power system configuration.
COPS: Critical Operating Power Systems
Code Requirements
Under the new
requirements from the
U.S. Department of
Homeland Security (DHS),
critical sections of the
U.S. economy will be
required to protect the
functionality and availability
of their systems: electric
power, information and
communications, banking
and finance, oil and gas, rail
and air transport, and water
[1]. The current revision
of the National Electric
Code, hereafter referred to
as the Code, covers three
classes of power systems.
These three classifications
of power systems are
emergency power systems,
legally required power
systems, and optional
standby power systems.
The requirements for these
power systems are detailed
in Article 700, Article 701,
and Article 702 of the Code
respectively [2]. Supporting
information on these power
systems can be found in the
series of ASCO Facts, NEC
Requirements for Transfer
Switches, parts one through
four.
In the sectors of information
and communications,
and banking and
finance, data centers
are important business
functions relied on for the
storage and processing
of information. To date,
power systems associated
with data centers have been
designed in accordance
with requirements for
optional standby power
systems; Article 702. These
requirements have served
the public well for decades,
but do not take into account
a class of power system
designed to protect the
interest or prosperity of the
U.S. economy.
Optional Standby
Power Systems
Optional standby power
systems are those systems
intended to supply power
to public or private facilities
or property where life safety
does not depend on the
performance of the system
[2]. Optional standby
power systems are
Article 702
Transfer Equipment
Article 708
Transfer Equipment
• Suitable for intended use
• Suitable for intended use
• Installed to prevent the inadvertent
interconnection of normal and alternate
sources of supply
• Installed to prevent the inadvertent
interconnection of normal and alternate sources
of supply
• Permitted for parallel operation with the
normal source shall meet the requirements of
Article 705
• Permitted for parallel operation with the
normal source shall meet the requirements of
Article 705
• Transfer switch is automatic and identified for
emergency use
• Means shall be permitted to bypass and
isolate the transfer equipment
• Shall be electrically operated and
mechanically held
• Shall supply only critical operating power
systems
• Branch circuits supplied by the critical
operating power system shall only supply loads
for critical operations
Table 1
considered to be less critical
than emergency or legally
required power systems,
and have less demanding
requirements. A synopsis
of the requirements for a
transfer switch for use in
an optional standby power
system is located in Table 1.
Transfer switch equipment
must be suitable for use,
and shall prevent the
inadvertent connection of
the primary and alternate
source. Additionally,
there are no specifications
regarding the technology
of the transfer switch.
Transfer switch equipment
in optional standby power
systems can be either
mechanical or electrically
operated mechanically held.
More detailed information
on optional standby power
systems can be found in
ASCO Facts titled NEC
Requirements for Transfer
Right: This chart (figure 2)
determines the code requirements
each state adopted.
Switches – Optional
Standby Power Systems
Part V of V.
With few exceptions, the
businesses in these sectors
are private organizations
that are not under control
of governmental agencies.
The exception is air
transport, where the Federal
Aviation Administration
(FAA) has control over
air transportation,
and water, where
municipal governments
typically control the
water supplies to their
residents. Organizations
in these sectors have
used optional standby
power systems because
they are commercial and
not directly related to life
safety. However, based on
past catastrophes and the
potential for damage to
the economy of any future
catastrophic event, optional
standby power systems
do not pro-vide adequate
redundancy, availability, or
performance requirements
needed to ensure the
continued vitality of the U.S.
economy.
Critical Operating
Power Systems
To address these new
requirements, another
power system needs to be
defined and be subjected
to specific installation
requirements to en-sure the
safety of the equipment.
Slated for adoption in the
2008 version of the Code,
critical operating power
systems will enter into the
equation.
The requirements for critical
operating power systems
will be located in Article
708 of the Code. Critical
operating power systems
are defined as “those
systems that are intended
to supply, distribute,
and control electricity to
designated vital operations
in the event of disruption
to elements of the normal
system” [3].
Critical operating power
systems will be “those
systems that are classified
by federal, state, municipal,
or other codes, by any
governmental agency
having jurisdiction or
by facility engineering
documentation establishing
the necessity for such a
system” [3].
The Article 708 covers a
number of aspects (e.g.
wiring, surge suppression,
transfer switch equipment,
grounding, risk assessment,
etc.). This issue of ASCO
Facts covers only those
articles associated with
transfer switch equipment.
For a complete listing of the
requirements, the Code and
any proposals should be
consulted.
detailed in Article 702 and
the Article 708 [2][3]. As
noted, the transfer switch
equipment designed for use
in Article 702 and Article
708 applications must be
suitable for the intended
use and shall prevent the
inadvertent interconnection
of primary and alternate
power systems. This
requires that the transfer
switch equipment be
evaluated to Underwriters
Laboratories Standard for
Safety, Transfer Switch
Equipment (UL 1008).
Table 1 shows a comparison
of the Code requirements
for transfer switches
However, that is where
the similarities end.
Transfer switch equipment
Figure 1
intended for installation in a critical
operating power system shall be
automatic and intended for use in an
emergency system [3]. The transfer
switch shall be electrically operated
and mechanically held, and “shall
only supply critical operating power
systems” [3]. Additionally, critical
operating power systems must be
isolated from non-critical operating
power systems, see Figure 1. From
these requirements, transfer switch
equipment intended for installation
in a critical operating power system
has more in common with the
requirements for transfer switch
equipment intended for installation
in emergency (Article 700) or legally
required power systems (Article 701).
Where the Article 708 differs from
Article 700 or Article 701 is in the
transfer time between the primary
power source and the emergency or
alternate power source.
For emergency power systems, the
transfer time is ten (10) seconds or
less [2]. For legally required standby
power systems, the transfer time in
sixty (60) seconds or less [2]. There
is no transfer time requirement for a
critical operating power system.
However, the assumption is made that
the transfer time between the primary
source and the alternate source must
occur before the stored energy in bat-
teries or flywheels is depleted.
Adoption of NEC 2008
Through the Occupational Safety
and Health Act of 1970, OSHA is
responsible for all standards that
affect the safety of personnel in the
workforce. In general, the scope of
OSHA includes those workplaces
associated with all public and private
organizations, and the utilization of
commercial equipment. Since OSHA
is responsible for safety, all laws or
standards that are adopted by OSHA
are mandated requirements.
States are responsible for passing
laws, statutes, or ordinances, to
meet the requirements for workplace
safety. For items related to the safe
installation of electrical equipment
or an electrical system, the primary
document used by the states is the
Code. A majority of the states have
adopted the Code for requirements
concerning the safe application of
electrical equipment. The time line of
adoption varies among the states. At
the time this article was written, the
1999, 2002, and 2005 revisions of the
Code were in use.
A minority of the states defer code
requirements to local municipalities.
As noted in Figure 2, those States
are Arizona, Delaware, Mississippi,
Missouri, Oklahoma, and South
Dakota.
The 2008 revision of the Code will
be released to the public in 2008
November. It is hard to predict when
states or municipalities will adopt the
2008 Code. However, states such
as Florida, Idaho, Iowa, Kentucky,
Louisiana, Minnesota, Nebraska, North
Carolina, North Dakota, Ohio, Oregon,
Texas, Utah, Washington, Wisconsin
and Wyoming have adopted the 2005
Code, so the presumption is that these
States will also adopt the 2008 Code
sometime in calendar year 2008.
References
1. Fairley, P (2004). The Unruly Power
Grid. IEEE Spectrum (North American
Version). 2004 August.
2. National Fire Protection Association
(2005). National Electric Code. NFPA
70-2005, Quincy, MA USA.
3. National Fire Protection Association
(2006). Article 585, Critical Operating
Power Systems. Available [on-line]
http://www.nfpa.org/Assets/Files/
PDF/ROP/70-A2007-ROC.pdf.
Retrieved 2007 May 04.
4. Occupational Safety and Health
Administration (2007). Available [online] http://www/osha.gov. Retrieved
2007 April 07.
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