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

7.1.5 Grounding
All instruments are capable of developing internal faults; the instrumentÕs power supply should be properly
grounded through a three-wire cord. Faults may also develop in the attenuator modules receiving the input
voltage sense leads. The attenuator should be tied through an effective grounding path to the measured
circuit ground reference. If the attenuator ground is connected to the power supply or chassis ground (as is
common), an inadvertent ground loop may result as shown in Þgure 14. In this case, the equipment power
supply grounding means should not be isolated. See 7.2.3. 
7.1.6 Sense lead overcurrent protection or current limiting
Fused voltage sense connectors are available and are recommended. Connections should always be made
downstream of existing overcurrent protection devices.
7.1.7 Routing of sense cables (strain relief)
Sense cables should be routed away from exposed conductors, sharp objects, electromagnetic Þelds, and other
adverse environments. They should be strapped or tied to a solid object to prevent inadvertent disconnection.
Figure 14ÑGround loops introduced by monitoring instrument

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IEEE
Std 1159-1995
IEEE RECOMMENDED PRACTICE FOR
38
7.2 Monitoring location
7.2.1 Objective
The characteristics of some power system variations will change depending on the monitorÕs proximity to
the source, the distribution system impedances, and the dynamics of the load. As an example, a voltage tran-
sient will dissipate energy through impedances that will change the leading edge rise time, peak amplitude,
and oscillation frequency.
The initial location to install a power quality monitor will be dependent upon the objective of the survey. If
the monitoring objective is to diagnose an equipment performance problem then the monitor should be
placed as close to the load as possible. This applies to performance problems with both sensitive electronic
loads such as computers and adjustable speed drives, and electrical distribution equipment such as circuit
breakers and capacitors. After the voltage ßuctuations are detected, the monitor may be moved upstream on
the circuit to determine the source of the disturbance.
If the affected equipment is currently supported by a means of power conditioning or Þltering, a decision
must be made as to the sequence of monitor placement. At the minimum, a monitor should be installed at the
affected equipment attachment location to the electrical supply (between the power conditioning equipment
and the affected equipment). This will determine if the power supplied to the device falls within the manu-
facturerÕs recommended operational speciÞcations.
Once this characterization has been made, the monitor can be relocated to the input (source) side of the
conditioning device or Þlter in order to determine whether the level of disturbances presented to it are within
its conditioning or Þltering capability. If the disturbances fall within this range, attention should be directed
to whether the conditioning or Þltering device is defective or if an interaction is occurring between the load
and the conditioner or Þlter. 
If the monitoring objective is to investigate the overall quality of a facility then the monitor should be placed
on the secondary of the main service entrance transformer, which is usually 600 V class service equipment.
The monitor will record the quality of power supplied to the facility as well as the effect of major loads
within the facility. The monitor may then be moved downstream in the electric distribution system to record
the power quality on individual feeders.
If harmonics are of concern, the monitor should be placed at capacitor or Þlter locations to measure har-
monic currents and distorted voltage. Capacitor magniÞcation of switching transients can also be investi-
gated by connecting a monitor at the capacitor bank. Refer to Þgure 15.