Ieee std 1159-1995, ieee recommended Practice for Monitoring Electric Power Quality

7.2.3 Diagnosing an equipment performance problem
The power quality monitor should be placed as close to the symptomatic load as possible. A physical inspec-
tion should be made to ensure that Þlters, transformers, or other treatment devices are not connected between
the monitor and the symptomatic load. The monitor should be connected to mirror the electrical connections
of the loadÕs power supply, as mentioned earlier. This installation will permit the monitor to record the abso-
lute magnitudes of voltage ßuctuations that are directly being applied to the load without the effect of circuit
impedances and Þltering. This location will also permit monitoring of the loadÕs direct current bus (power
supply output) or communications ports without extended runs of monitor leads.
If the symptomatic load is powered from a wall receptacle, then the monitor should be connected to a spare
receptacle in the same outlet. If this is not possible, then a receptacle in an adjacent outlet may be used, but it
should be electrically veriÞed that this receptacle is on the same circuit as the load and that it is wired properly.
Figure 15ÑSuggested monitoring locations on a typical low voltage system

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IEEE
Std 1159-1995
IEEE RECOMMENDED PRACTICE FOR
40
To monitor the power to a load connected to an isolated-ground receptacle (orange in color), the power
monitor should be connected to the same receptacle. These receptacles are designed for use with two
grounding conductors. The non-insulated grounding conductor (sometimes conduit) is bonded to the outlet
housing. The isolated grounding conductor (green-insulated wire) is terminated at the receptacle grounding
terminal. The preferred practice is not to daisy-chain the isolated grounding conductor but to run a separate
insulated green wire from the isolated ground bus in the subpanel, or separately-derived source, to each
orange receptacle. (See article 250-74, exception number 4 in the NEC [B2].) 
It is sometimes impossible to connect the monitor at the load. Voltage connection points may be inaccessi-
ble; the load may be in a hazardous environment or there may be security considerations. In this situation the
monitor may be connected at the closest subpanel feeding the load. Monitoring at a subpanel has the advan-
tage that the circuit conductors are accessible for current measurements.