33 5.12 Loose Neutral
if the difference is 16 volts, then there must be at least a 16 volt separation
between the two legs. The range is a voltage that specificies how close the sum
of the two voltages must be to twice the nominal. For example, a range of 12
volts means that the sum of the two legs must be within 12 volts of twice the
nominal voltage. Both the range and the difference conditions must be met
for at least the number of seconds specified by the duration. If the duration
is set to 5 seconds, then the difference and range conditions must be met for
5 consecutive seconds before a loose neutral is declared. One-second average
voltages are used. The nominal voltage is the nominal determined during the
two minute countdown by the Abnormal Voltage record type, and is typically
120 volts in a single-phase hookup.
As an example, assume the difference parameter is 16 volts, and the range
12 volts, with a duration of 5 seconds. The two line voltages are 119 and
121 volts. Then one leg moves to 128 volts, and the other to 110 volts.
The difference between the two legs is 18 volts, which meets the difference
threshold. The sum of the two voltages is 238 volts, which is within the
required 12 volts (specified by the range value) of twice the nominal (240
volts). If these voltages persist for 5 seconds in a row, then a Loose Neutral
record will be triggered.
If one voltage leg changes due to heavy loading, the range parameter keeps
the loose neutral from false triggering. For example, if the voltages start at
119 and 121 volts, then a heavy load to channel 1 causes it to drop to 105 volts,
with the other leg still at 121, the difference condition is met (121 • 105 > 12),
but the range condition is not met: 105+121 = 226, and 226 volts is not within
12 volts of the 240 volt nominal.
5.12.2 What’s Recorded
The date and time of the loose neutral triggering is recorded, along with the
voltage on the two channels. Only the first occurrence of a Loose Neutral is
recorded; if the conditions are met again, nothing further happens. The Loose
Neutral report shows whether the neutral may have a bad connection, not the
exact times the connection was made and broken.
5.12.3 Typical Settings and Suggested Uses
The Loose Neutral Report can show the symptoms of an actual loose neutral
connection. It is worth investigating if the report is triggered. However, it
is possible for the Loose Neutral logic to be fooled. If both legs are equally
loaded, then the two voltages will remain the same even if the neutral is
removed. This will prevent the Loose Neutral trigger from firing. It is also
