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

7.3.4 Hard-wired connections
For long-term monitoring, hard wire connections should be made. The connecting means should be in
conformance with other applicable standard practices or code requirements. It should be ensured that the ter-
minating means is compatible with the wire type. 
7.3.5 Plug and receptacle type connections
Standard three-wire sense cords are usually supplied with the instruments for standard National Electrical
ManufacturerÕs Association (NEMA) outlet connections. The outlet should be checked Þrst for wiring errors
such as reversed polarity and open ground. Inexpensive circuit checkers are good for Þnding simple errors
but should not be relied upon for ensuring the wiring integrity. Sense cables for other than 15 A single-phase,
grounded receptacles may not be supplied with the instruments. If one is required, break-out cords are often
constructed to accommodate the need. Caution should be exercised so that the connectors used do not violate
their listed purpose.
7.3.6 Quality of voltage sense connections
The voltage sense connections represent the interface between the power system and the monitor. They are
an extension of the monitorÕs inputs, not an extension of the power system. This means that any loose
connection or faulty cable should be remedied before useful data can be recorded. Otherwise, the distur-
bance data may be the result of the connection and not of an anomaly in the system.
When an enclosure is opened to allow connections of the power line monitor, the integrity of the equipmentÕs
shielding has been compromised, which may introduce an artifact in the monitoring, or may affect equipment
operation. Monitoring equipment sense leads are particularly susceptible to EMI/RFI. To minimize the
erroneous effects, two wires should be run to each monitoring channel input and not the popular one wire per
channel with a single common or other daisy-chained connection. Twisted pair and/or shielded input wiring
is desired yet not typically provided. In some cases, analyzers have incorrectly reported events such as
transient voltages that resulted from sense wiring crosstalk or EMI/RFI. This is particularly troublesome
when the monitors are available with very low disturbance thresholds (e.g., 25Ð50 V on a 480 V system).
Shielded input sense cables are not readily available, but practical techniques should be employed to reduce
EMI/RFI interference. For example, two wires per channel can be used. These wires should be twisted
together and routed against the grounded enclosure chassis instead of looped out in free air.