ACM20 Series
Four-Function AC Power Meters
4. Wiring:
All power supply wiring must be rated for the voltages and
currents they will carry and must comply with any code or applica-
tion-mandated requirements pertaining to the user’s specific installa-
tion.
5. Supply Fusing, and Grounding:
ACM20 power meters are not inter-
nally fused. If supply fusing is required it must be externally installed
according to the supply wire’s maximum amperage rating. No con-
nection is required to earth/chassis ground.
ACM20 power meters draw minimal steady-state supply currents
(110mA max.), and in most applications can be fused according to the
supply wire’s maximum amperage rating. However, these models can
draw significantly higher surge currents for brief periods when the ac
line voltage is initially applied to TB1.
6. Current Transformer Polarity:
In order to perform accurate Watts
and Power Factor measurements, connections to the two rear power
supply inputs, TB1-A and TB1-B, and built-in current transformer L1
must have the proper polarity. That is, the load current flowing in the
wire passing through L1's center hole must have the same polarity as
the line voltage connected to TB1-A and TB1-B.
The wiring diagrams in Figures 1-4 ensure that, for a purely resistive
load, current flowing in current transformer L1’s primary circuit will
have the same polarity as the applied voltage at TB1. If proper polarity
is not followed, the Watts and Power Factor readings will be zero. To
correct a zero Watts reading, simply reverse the direction of the load
wire passing through the hole in L1.
7. Connector Torque Ratings: It
is important to tighten TB1’s, screw-
terminals to their rated torque specification of 3.6 pound-inches
(0.4Nm). Proper tightening will minimize connector losses and ensure
safe, reliable operation.
8. Isolation:
Except for the 2-56 thread metallic mounting studs, all of
the ACM20 power meter’s internal components (printed circuit board,
resistor, capacitors, current transformer L1’s secondary leads, etc.)
are at the ac-mains potential connected to TB1. ACM20 power meters
are designed to measure and be powered from one ac power-source
only. Any other connection schemes will introduce significant mea-
surement errors.
TYPICAL WIRING DIAGRAMS
120 V
LOAD
Epoxy encapsulation
Note: If the ACM20 displays zero Watts with
power applied to the load, reverse the direction
of the wire passing through the CT's center hole.
See Technical Note 6 for more information.
Polarity dot on bottom
B
A
TB1
H
N
120 Vac (50/60 Hz)
Figure 1. Wiring diagram for 110/120V single phase systems
www.murata-ps.com/dpm
30 Apr 2010
email: sales@murata-ps.com
MPM_ACM20 Series.A06
Page 3 of 6
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