Facility Management Power Study Services
The health of a facility’s electrical system is not
as all the equipment is braced properly and no
something a Plant Engineer or Facility Manager may
think about, but it is definitely something to be
system modifications are required or equipment
examined. Could you imagine if your facility lost
power to half of its operation due to an overload
from a space heater? Or have your main distribution
panel be damaged and the facility be without power
for days or weeks? A Power Study is required to
meet code and helps minimize outages. It gives a
picture of the stability of an electrical system and its
ability to withstand an electrical fault with minimal
disruption to a facility’s operation. A Power Study
consists of three items: 1) a Fault Current Analysis,
2) Overcurrent Device Coordination, and 3) Arc
Flash Hazard Analysis. An OSHA required Arc Flash
Hazard Analysis could be performed without a
Device Coordination study, but a Fault Current
Example of Fault Current Analysis Results
Analysis would have to be performed.
Fault Current Analysis
Fault current analysis gives a picture of the electrical
system’s ability to withstand an electrical fault with
minimal damage to the system.
A fault is an
abnormal electrical current that bypasses the normal
load, typically a short circuit. The current is of high
magnitude and the duration is typically short, with
the fault being rapidly cleared by an upstream
protective device. The study compares the
calculated fault current to the equipment bracing.
The
study
also
lists
equipment
modification/replacement
recommendations
necessary to bolster the distribution system to allow
it to safely withstand a fault. Equipment bracing is a
value, typically in thousands of amps, that a piece of
electrical equipment is designed to withstand without
catastrophic damage occurring. The fault current
study should be updated when major changes to the
electrical system are made or every five years to
capture changes to the utility systems feeding your
facility. The results of the analysis can be as simple
could be found to be over-dutied and in need of
replacement. A fault current study will allow for this
expense to be planned versus having to contract an
emergency repair. An emergency repair would be at
a much higher cost with the associated disruption to
business operations.
Overcurrent Device Coordination
When
occurs,
a
fault
the
overcurrent
protective devices
in the system
operate and open
the
electrical
current path to
clear the fault.
Overcurrent
protective devices
are designed to
open the electrical
Time Current Curves showing proper
overcurrent device coordination.
circuit when the current rises above a predetermined
value. Examples of these are circuit breakers, fuses,
This incident energy information is communicated to
employees,
and medium voltage relays.
contractors, and the
A properly coordinated system will localize the
public by way of the
arc
flash
label
outage to as close to the fault as possible. Proper
coordination is achieved by comparing the time
provided as part of
the study. Proper
current curves of the overcurrent devices to ensure
that a device closest to a fault clears the fault and no
arc flash labeling
allows employees to
other devices operate. This proper coordination
safely
helps ensure that a faulty lighting fixture or a single
faulty motor does not cause a system wide power
equipment without having to wear unnecessary
personal protective equipment.
outage. Some circuit breakers have adjustable
settings to help achieve coordination, while devices
The arc flash hazard calculations are required to be
such as fuses have a fixed performance. This lack of
updated every five years or after significant changes
adjustability can cause issues in achieving a fully
coordinated system. Proper device coordination can
to the electrical system occur.
also be utilized to reduce the Arc Flash Hazard of an
electrical system.
Conclusion
Arc Flash Hazard Analysis
The arc flash hazard analysis is the largest part of a
safety and maintaining business operations, along
with being a guide for what is required for system
power study as it relates to personnel safety. An arc
operation. With a proper understanding of the health
flash is
part
of
an arc fault, a type of
of the electrical system, a proper maintenance plan
can be developed versus having to react to an
electrical explosion that
results from a low-
unplanned event.
impedance connection
to ground or another
Aftermath of an Arc Flash Event
voltage phase in an
electrical system.
Calculation of incident energy for an arcing fault is
based on available fault current and protective
device clearing time and is expressed in
2
calories/cm . This energy release can be from a
small flash of light to a full explosion and associated
fire. Responsibility for these calculations are
placed on the facility owner per the NFPA 70E the National Fire Protection Association’s
standard for electrical safety in the workplace
and OSHA regulations.
perform
work
Typical Arc Flash Label
on
energized
electrical
The importance of a proper power system study
cannot be stressed enough as it relates to personnel
References and Further Reading
IEEE Standard 551 (Recommended Practice for
Calculating Short-Circuit Currents in Industrial and
Commercial Power Systems) 2006
NFPA 70E: Standard For Electrical Safety In The
Workplace, 2015
National Electric Code (NEC) 2014
About the Author
Jeff Balster P.E., is an Electrical Engineer for
PEDCO. He has been involved in the design of
electrical facilities for industrial, commercial, and
institutional buildings with primary responsibilities for
lighting, power distribution, power system studies,
communication and data systems and other auxiliary
systems.