Model: PM-2160-A
Doc. Ref. no. : - m20Aom201
Issue no. 02
Page 21 of 36
User’s Manual
6.4 PTs and CTs
Large electrical installations have high voltages and currents, which may exceed the direct
connection rating of the meter. In this case, Potential Transformers (PTs) and Current Transformers
(CTs) are used to precisely “step down” or reduce the voltage and current level to suit the meter
rating. Potential Transformers usually have a full-scale output of 110V ac RMS line-line and Current
Transformers, a full-scale output of 5A or sometimes 1A.
The PTs (Potential Transformers) and CTs (Current Transformers) must be planned, installed
and tested by a qualified electrical contractor before wiring the meter. The accuracy of the
measurement also depends on the accuracy and phase
– angle error of the PTs and CTs. Instrument
Class 0.5 or better PTs and CTs are recommended. Do not use protection class CTs to feed the
Multifunction meter 2160-A; as they have poor accuracy and phase characteristics.
Ensure that the CT primary rating has been selected so that your normal load variation lies
between 40% and 80% of its full scale. If your CT is over-rated, say if the load is always less than
10% of the CT primary rating, accuracy suffers.
6.4.1 PT, CT Wiring
The PTs and CTs must have adequate VA rating to support the burden (loading) on the
secondary. You may want to support the auxiliary supply burden from one of the PTs. CT wiring can
impose additional burden (loading) on the CT. For example, if the CT has a 5A secondary and the
wire resistance is 1.0 Ω, then the CT has to support an additional burden of 5VA. The wiring distance
from the CT secondary to meter should be such that, VA of wire path between meter and CT along
with VA of meter should not exceed the VA rating of CT, otherwise the CT could get over-burdened
and give large errors.
Multifunction meter PM-2160-A should be conveniently located for easy connections of
voltage (PT) and Current (CT) signals.
Note:-
Common Modbus details are given in following chapter, all above mentioned features are
available as described based on model selection.
