Rockwell Automation 1404-M4_M5_M6_M8 Powermonitor 3000 Installation Instructions, PRIOR to Firmware rev. 3.0 - Manual (Page 17)

Publication 1404-IN007D-EN-P - October 2004
Powermonitor 3000 17
See Figure 41 on page 56 for mounting hole dimensions. Mount the
Master Module with four (4) No. 8-32 UNC or M4 screws with flat
washers and lock washers.
System Accuracy
Considerations User supplied potential transformers (PTs) and current transformers
(CTs), as well as wiring from the CTs to the Powermonitor, may
reduce the accuracy of your Powermonitor 3000 system. The quality
of the Powermonitor 3000’s measurements can be no better than the
quality of the signals presented to its input terminals. It is the user’s
responsibility to select transformers that are adequate for the desired
metering accuracy.
ANSI/IEEE C57.13, Requirements for Instrument Transformers, defines
three classes of transformer accuracy: class 1.2, class 0.6, and class 0.3.
The application should dictate the transformer accuracy class to be
used.
PTs and CTs may introduce errors in three areas: ratio errors, phase
errors, and bandwidth errors.
Ratio Errors
The voltage ratio of a PT is the number of primary turns of wire
divided by the number of secondary turns. Manufacturing tolerances
may cause the ratio to be slightly different than the design specifies,
causing an error affecting the voltage input to the Powermonitor 3000.
Likewise, the current ratio of a CT is a function of the ratio of the
number of turns of wire on the primary and secondary. Some error in
this ratio is quite common in commercial grade PTs and CTs.
Other errors include magnetic core losses, winding impedance, and
the burden, or load, on the transformer secondary. The combination
of these errors is known as “Ratio Error”. You may compensate for
Ratio Error, if known, by adjusting the Basic Configuration entries for
PT and CT primary or secondary voltages.
IMPORTANT
Use caution not to block the ventilation slots of the
Master Module. All wiring and other obstructions
must be a minimum of 50 mm (2.0 inches) from the
top and bottom of the unit.