ACA-20RM Datasheet, PDF (3/5 Pages) Murata Power Solutions Inc. – True-RMS-AC Ammeters with Built-in CT

The calibration potentiometer has approximately ¾ of a turn of rotation;
do not force its adjustment screw past the end stops. Contact MPS if
additional information is required regarding calibration, setup, or any
other technical issue pertaining to ACA-20RM ac ammeters.
3. Wire Gauges and Fusing: Use only the wires specified under the
Functional Specifications Section when making connections to ACA-
20RM Series ammeters. All power supply and load wiring must be
adequately rated for the supply voltages and currents they will carry,
and they must comply with all code- or application-mandated require-
ments pertaining to the user’s installation.
The supply wires connected to ACA-20RM ammeters must be fused
in accordance with applicable regulatory codes. Also, wire insula-
tion should be stripped to within +/-10% of the stated dimensions;
wires should be inserted into TB1 such that the screw terminal does
not pinch their insulation. TB1 can only used for supplying power to
the meter’s internal circuitry; it must not be used to supply current to
external loads.
AC-powered models draw minimal steady-state supply currents (less
than 0.050A) and they can be fused according to the supply wire’s
maximum amperage rating. However, these models can draw higher
surge currents for brief periods (in the microsecond range) when power
is initially applied.
WIRING DIAGRAMS
First pass and carefully dress one external load wire through L1, then
connect the AC supply and load wires to TB1 as shown. Ensure all wires
are stripped and properly tightened. For accurate operation, make only
BACK VIEW
A
FUSED AC POWER
TB1
B
TO AC LOAD
L1
FROM AC SUPPLY
Figure 2. Connections for pc-board mounted CT's
ACA-20RM Series
True-RMS-AC Ammeters with Built-in CT
4. AC Supply Polarity and Grounding: The two supply inputs, TB1
‘A’ and ‘B’, on ACA-20RM ammeters are not polarity sensitive, that
is, they have no ‘AC LO’ or ‘AC HI’ designations. Also, ac-powered
ACA-20RM ammeters do not include or require a connection to earth/
chassis ground.
5. Connector Torque Ratings: Be sure to tighten TB1’s screw-terminals
to 3.6 pound-inches (0.4Nm). Proper tightening will ensure reliable
long-term operation.
6. Isolation: The on-board CT (L1) provides a minimum of 2000Vdc iso-
lation between the current-carrying load conductor passing through
its opening and the ammeter’s power source that’s connected to TB1.
Of course, this isolation rating applies only to applications where the
load wire does not connect directly or indirectly to TB1-A or TB1-B
(i.e., where two different ac supplies are involved).
7. Split-Core CT (Clamp-on) Models: 50A models feature a split-core
current transformer that can be clamped around a current-carrying
load conductor without having to disconnect or remove power from
the load’s power source. This live-connection capability can only
be used if the load’s power source is isolated (see technical note 6)
from the ammeter’s own power source that’s connected to TB1.
The ammeter’s ac power supply must always be denergized before
making connections to TB1. Refer to the ‘Panel Installation’ section of
this data sheet for additional information.
one pass with load wire through the on-board CT (only one primary turn).
For split-core CT models, make sure to fully engage the CT's Locking
mechanism
A
FUSED AC POWER
B
BACK VIEW
TB1
L1
TO AC LOAD
FROM AC SUPPLY
Figure 3. Connection for flying lead CT's
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