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Untitled
42
C A P I T A L N O W
I
42
C A P I T A L N O W
Troubleshooting
continued on page 44
In an office building
,
regular equipment failure is
a big problem. It becomes
catastrophic in a hospital or
airport. Identifying the source of
such failures (usually, degraded
connections and wiring devices)
and resolving them can be a
frustrating experience.
Dont lose hope! It is
possible to quickly and easily
test a branch circuit, starting
at the outlet where the
malfunctioning device was
connected. What is required
are the right tools and proper
troubleshooting techniques.
Required tools include
voltage performance monitors and
branch circuit testers to determine
if the circuit or the voltage source
is to blame.
Single-phase branch
circuit testers and monitors
are inexpensive but also very
accurate. These small monitors
can be used to compare voltage
events captured at different points
in the facility, creating a power
quality survey.
Power quality surveys are
the most effective when they are
performed over a short period
and cover a large area. If, for
instance, voltage events happen
on branch circuits without
simultaneous voltage events at the
service entrance, it is a clue that
the individual circuit may need
attention.
Tools must be accompanied
by good techniques that break the
job down into manageable tasks
to verify that the branch circuit
is sound and actually provides
the clean voltage. Performing
the simple tests listed below will
ensure the integrity of branch
S
tep Up to Better

T
roubleshooting
Using the right tools and techniques can make
troubleshooting branch circuits a breeze.
By Brian Blanchette 44
C A P I T A L N O W
circuits and provide safe and reliable
equipment performance.
Branch circuit structure
Begin by evaluating the branch
circuit structure using a methodical
testing procedure.
Step 1:
Take voltage
measurements. This test can be
performed using a standard voltage
tester. RMS voltage should measure
between 108 and 132 volts. Voltages
outside these parameters cause
equipment problems and present a
safety hazard.
Step 2:
Test for correct wiring
polarity. Do this at the receptacle
by using a branch circuit tester to
determine the polarity of the wiring
and the presence of a ground.
Step 3:
Test for shorted neutral
and ground. If the neutral and
ground are shorted within 20 feet of
the outlet under test, readings may
indicate a false ground. The neutral
and ground must not touch anywhere
on the branch circuit.
Step 4:
Test voltage drop.
Voltage drop should never exceed
5% with a 15-amp load. If voltage
drops below 108, the circuit will
fail regardless of the percent
voltage drop.
Step 5:
Take impedance
measurements. Measure the
impedance of the equipment ground
conductor. If impedance values are
greater than 0.25 ohms, its possible
that a loose connection exists in
the circuit.
Also:
Measure impedance of
the hot wire and the neutral wire.
High impedance along the neutral
conductor path causes two problems:
increased voltage drop and increased
heat (that can cause re).
Compare resistance of the hot
wire and the neutral wire to quickly
determine if one or the other causes
voltage drop. If both are high,
the branch circuit might be too
long or the wire may be too small
for the task.
Monitor performance
If testing determines the circuit
is properly wired and well grounded,
its time to use a voltage monitor to
evaluate the quality of the energy
supplied at the power outlet.
Step 1:
Capture sag and swell
voltage disturbances. Connect a
branch circuit performance monitor
at the equipment location to capture
any disturbances on the line.
Monitors for this purpose are small
and can plug into the outlet itself or
into a power strip connected there.
Troubleshooting
continued from page 42

Voltage drop
should never
exceed 5% with a
15-amp load.
Troubleshooting
continued on page 46 46
C A P I T A L N O W
Troubleshooting
continued from page 44
The ITIC
standard can be
used to arbitrate
warranty versus
power quality
disputes.
Any sag or swell events along
with the exact day and time they
occur should be recorded for
later analysis. Sags and swells are
measured by the magnitude of
voltage deviations lasting a dened
period of time. Unimportant events
should be ignored. If there are no sag
or swell events, voltage quality can
be eliminated as a source of failure.
Note that voltage monitors
should use a standard, such as the
one published by the Information
Technology Industry Council (ITIC)
formerly known as SABEMA
to dene the operating range of
the devices.
Since the ITIC standard
is written to provide guidance
for manufacturers of computer
equipment, it is an excellent choice
to dene important voltage events at
outlets and at any point on a single-
phase distribution circuit. It can be
used to arbitrate warranty versus
power quality disputes, as well as to
qualify circuits before installation.
Step 2:
Monitor for voltage
transients. Voltage transients are
brief, repetitive, and very powerful
impulses of energy. Signicant
transients could be as brief as 4
microseconds, yet up to 4,000 volts.
Ensure that the duration of the
transient, the voltage, and the exact
day and time are recorded to enable
the troubleshooter to determine
if they played a role in a failure
and to help locate the source
of the transient.
If no transients are logged,
transient voltages can be eliminated
as a source of failure.
Step 3:
Monitor for total
harmonic distortion (THD). Voltage
distortion is measured as the
percentage of distortion caused by
harmonics up to the 50th. A sample
rate of 128 samples per cycle is
required to make this measurement.
IEEE 519 species the harmonic
limits. This standard allows for up to
5% THD on most branch circuits. A
special exception exists for hospitals
and airports, where the THD limit is
reduced to 3%.
Note all instances of THD
greater than 3%. Since harmonic
distortion is steady state rather than
rapidly changing, investigate any
reading greater than 3%. If THD is
below 3%, there is no problem, and
THD can be eliminated as a source
of failure. Blanchette is a eld sales engineer
for Ideal Industries, Inc.
Investigate any THD
reading greater than 3%.