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ACA-20RM Series
True-RMS-AC Ammeters with Built-in CT
MPM_ACA-20RM.C01 Page 1 of 5
Murata Power Solutions’ new ACA-20RM Series are the world’s fi rst digital ac-ammeters
to incorporate a built-in current transformer (CT) to directly measure the true-rms value of
complex, non-sinusoidal ac currents from 2 to 50A – no bulky and expensive 5A “donut”
CTs are required! Operation and setup is straightforward: simply pass the load-carrying
wire through the on-board CT, apply power, and the ammeter is fully operational.
Five input ranges measure 0-0.2 amps (0.1mA resolution), 0-2 amps (0.001A resolution),
0-20 amps (0.01A resolution), 0-30 amps (0.1A resolution) or 0-50 amps (0.1A resolution).
The 50A model features an oversized split-core current transformer that easily accommo-
dates wires sizes up to 4 AWG (21.2mm2). Two power supply options are available: 85-140V
(47-63Hz), and 170-264V (47-63Hz).
All models are totally self-contained; no external components are required. Power con-
sumption from a nominal 120V or 220V ac supply is less than 50mA. And, precision auto-
zeroing circuitry, super-stable components, and an rms-to-dc converter circuit combine to
achieve excellent performance when measuring the complex, non-sinusoidal, ac currents
found in today’s computer/telecom equipment.
ACA-20RM Series ammeters feature full-size, 0.37" (9.4mm) high, 3½ digit, bright red
LED-displays and a built-in bezel/fi lter assembly that features metal fasteners. They are
panel-cutout compatible with MPS’s DMS-20 Series of ac voltage and frequency monitors,
making ACA-20RM ammeters perfect replacements for older, less reliable, analog panel
meters in today’s sophisticated IT instrumentation.
FEATURES
Built-in CTs provide true-rms values of complex
waveforms
Perfect for measuring AC current in IT applications
Five ranges measure: 0-0.2A, 0-2A, 0-20A, 0-30A
and 0-50A
50A models features a split-core CT for easy installation
Self-powered from 85-140Vac or 170-264Vac
Large, easy-to-read, red LED display with 0.37" digits
Reliable single-board construction
Digital replacement for analog meters
Approvals to UL/cUL/IEC/61010-1
C
®
US E156931
CURRENT LIMITED
AC SUPPLY
3½ DIG IT
A/D CONVERTER
+V –V
–
+
RMS-to-DC
CONVERTER
CAL.
BUILT-IN
CURRENT
TRANSFORMER
LED DISPLAY
POWER
CONVERTER
TB1
AB
(L1)
MEASURED AC
LOAD CURRENT
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ACA-20RM Series
True-RMS-AC Ammeters with Built-in CT
MPM_ACA-20RM.C01 Page 2 of 5
TECHNICAL NOTES
IMPORTANT! To ensure safe and reliable operation, ACA-20RM
ammeters must be installed and serviced by qualifi ed technical
personnel after reading this data sheet in it's entirety. Contact Murata
Power Solutions if there is any doubt regarding their installation or
operation.
1. Measurement Type: ACA-20RM ac ammeters employ true-rms
input circuitry to measure the stepped-down output of their on-board
current transformers (CT). Stated accuracy is measured using a sine-
wave input at, or close to, the specifi ed full scale input, at a nominal
line frequency of 60HZ.
2. Calibration: Periodic recalibration of ACA-20RM ammeters is not
required under normal indoor environments. If user calibration is
deemed necessary, it must be performed by qualifi ed technical
personnel since potentially lethal voltages and currents are applied to
the ACA-20RM during the calibration process.
Calibration is performed with approximately 95% of the specifi ed
full-scale current fl owing through the ammeter’s built-in CT. A fully
insulated, non-metallic adjusting tool must be used to adjust the
calibration potentiometer, located on the back of the ammeter (see
Mechanical Specifi cations section).
Performance/Functional Specifi cations
Typical at TA = +25°C, unless otherwise noted.
Input Range:
0 = 199.9mA
1 = 1.999A
2 = 19.99A
4 = 50.0A (with split-core fl ying-lead CT)
5 = 30.0A (with fl ying-lead CT)
Ordering Information
ACA-20RM- 1 - AC3 - R L - C
Power:
AC3 = 85-140Vac@50/60Hz
AC4 = 170-264Vac@50/60Hz
LED Color:
RL = Low-Power Red
Accessories:
DMS-20-CP Panel Cutout Punch
➀ Specifi ed full-scale currents are those passing through the ammeter’s built-in
current transformer’s primary load-circuit. See Notes 2 and 3 below for ad-
ditional model-specifi c information.
➁ The overcurrent rating of 1.5 x the rated full-scale current is a continuous rating
and applies to the current passing through the built in current transformer only,
it does not apply to any external circuit-wiring or external loads. Accuracy is
guaranteed up to the rated current level.
➂ Specifi ed accuracy applies to inputs with crest factors (CF) up to 2.0, where CF
= Vpeak/Vrms. Crest factors of 2 to 5 introduce an additional error of ±3% of full
scale. Ammeters are calibrated with a near full-scale 60Hz sine-wave current
fl owing through the ammeter’s built-in CT.
➃ All specifi ed maximum power supply currents are steady state; larger surge
currents can occur at initial application of line power.
Add -C for RoHS
Rated Full-Scale Current ➀Min. Typ. Max. Units
ACA-20RM-O-ACX-RL – – 199.9 mA
ACA-20RM-1-ACX-RL – – 1.999 A
ACA-20RM-2-ACX-RL – – 19.99 A
ACA-20RM-4-ACX-RL – – 50.0 A
ACA-20RM-5-ACX-RL – – 30.0 A
Overcurrent Rating ➁ 1.5 x Rated Full-Scale Current
Performance
Sampling Rate 2.5 Samples per second
Accuracy ➂±0.4%FS ±3 Counts with 60Hz
Sine-Wave Input
Measurement Type RMS Responding, Crest Factors of 1-5
Temperature Drift (0 to 60 °C) – ±0.2 ±0.4 Cnts/°C
Zero-Current Reading (within
30 sec.)
–001 000 001 Cnts
Dielectric Withstanding Voltage 2000 – – Vdc
UL/IEC61010-1 Measurement category II
Power Supply Voltage
ACA-20RM-X-AC3-RL 85 120 140 Vac/47-63Hz
ACA-20RM-X-AC4-RL 170 220 264 Vac/47-63Hz
Power Supply Current ➃
ACA-20RM-X-AC3-XX – 30 50 mA/47-63Hz
ACA-20RM-X-AC4-XX – 30 50 mA/47-63Hz
Power Supply Terminal Block
Wire Size 16-22AWG, Solid and stranded
Insulation Strip Length 0.250 inches
Screw Tightening Torque 2.2 lb·in (0.25 N·m) ±20%
Rated Voltage 310Vac
Display
Display Type and Size 3½ Digit Red LED, 0.37"/9.4mm High
Overrange Indication “1___”
Decimal Point Fixed, model dependent
(see full-scale input Current)
Physical/Environmental
Operating Temperature 0 – +60 °C
Storage Temperature –40 – +75 °C
Humidity –40 – +95 %
Dimensions (non-condensing) Model dependent, see page 3 & 4
Weight
ACA-20RM-0,1,2-XXX-XX 1.1 ounces (31 grams) nominal
ACA-20RM-4-XXX-XX 2.1 ounces (60 grams) nominal
ACA-20RM-5-XXX-XX 1.5 ounces (43 grams) nominal
See www.murata-ps.com/dpm-availability for model-specifi c availability.
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ACA-20RM Series
True-RMS-AC Ammeters with Built-in CT
MPM_ACA-20RM.C01 Page 3 of 5
WIRING DIAGRAMS
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 note6)
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.
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
Figure 2. Connections for pc-board mounted CT's
FROM AC SUPPLY
TB1
L1
TO AC LOAD
BACK VIEW
A
B
FUSED AC POWER
Figure 3. Connection for fl ying lead CT's
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: Wires specifi ed in the Functional Specifi -
cations section must be used for making connections to ACA-20RM
series ammeters. All power-supply and load wiring must be rated for
the supply voltages and currents they will conduct and must comply
with any code or application-mandated requirements pertaining to the
user’s specifi c installation.
ACA-20RM ammeters are not internally fused. Terminal block TB1 is to
be used only for powering the ammeter’s internal circuitry; it must not
be used to supply power to external loads. The supply wires feeding
these ammeters must be fused with a 0.25A/250V time delay/time lag
fuse, in accordance with applicable regulatory codes.
Wire insulation must be stripped to within ±10% of the stated dimen-
sions, and wires should be inserted into TB1 such that their insulation
is not pinched by the screw terminal.
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 amme-
ters do not include or require a connection to earth/chassis ground.
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
BACK VIEW
TO AC LOAD
A
B
FUSED AC POWER
FROM AC SUPPLY
TB1
L1
F R O N T V I E W
1 . 2 8 0
( 3 2 . 5 1 )
0 . 1 8 7
( 4 . 7 5 )
R E C O M M E N D E D D R I L L A N D
P A N E L C U T O U T D I M E N S I O N S
1 . 8 2 6 ( 4 6 . 3 8 )
0 . 8 3 8
( 2 1 . 2 9 )
1 . 6 2 6 ( 4 1 . 3 0 )
1 . 0 7
( 2 7 . 1 8 )
I N T E R N A L C O R N E R R A D I I :
0 . 0 3 2 ( 0 . 8 1 ) M A X .
0 . 0 9 3 ( 2 . 3 6 2 ) D I A M E T E R ( 4 R E Q U I R E D )
0 . 1 1 6 ( 2 . 9 5 )
1 . 3 3 6 ( 3 3 . 9 3 ) 0 . 1 4 5 ( 3 . 6 8 )
0 . 69
(17.5)
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ACA-20RM Series
True-RMS-AC Ammeters with Built-in CT
MPM_ACA-20RM.C01 Page 4 of 5
PANEL INSTALLATIONS
BEZEL AND PANEL CUTOUT
All connections to ACA-20RM Series ammeters must be made after the
ammeter is securely attached to its panel and with all associated load
and supply voltages de-energized (off). However, using extreme caution
and observing all safety measures applicable to the user’s installation,
50A split-core CT models can be connected to energized current-carrying
load conductors, but connections to TB1 must always be made with the
ammeter’s power source off.
Care should be exercised when passing the load-carrying conductor
through the meter’s built-in CT—particularly when larger conductors are
used. The installed wire-positions should be such that minimal mechani-
cal forces are applied to the built-in CT, TB1, or to the ammeter itself. In
high-vibration environments, it is strongly recommended that adequate
strain reliefs be used for all load and supply wiring.
Figure 4. Panel Installation
Using Figure 4 as a guide, carefully insert the bezel/color fi lter assembly
into the panel opening. From the rear of the panel, install the four round
plastic standoffs over the bezel’s threaded studs. Install the pc-board
assembly; then attach and securely tighten each of the four hex nuts
to 15-20 ozf-in (0.106 to 0.140 N-m). Use only the factory-supplied
hardware as the use of substitute hardware could result in an unsafe
installation and/or adversely affect the reliability of the ammeter itself.
The recommended range of panel thickness that can be used with the
supplied hardware is 0.040 inches (1.0mm) to 0.125 inches (3.2mm).
Panel thickness outside of this range will require additional user-supplied
hardware and/or modifi cations.
3)$%6)%7
"EZEL
'ASKET 3TANDOFF
.UT
!#!2-
!#!MMETER
"OARD#UTOUT
PANEL
'ASKET 3TANDOFF
4HICK
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Murata Power Solutions, Inc. makes no representation that the use of its products in the circuits described herein, or the use of other
technical information contained herein, will not infringe upon existing or future patent rights. The descriptions contained herein do not imply
the granting of licenses to make, use, or sell equipment constructed in accordance therewith. Specifi cations are subject to change without
notice. © 2015 Murata Power Solutions, Inc.
Murata Power Solutions, Inc.
11 Cabot Boulevard, Mansfi eld, MA 02048-1151 U.S.A.
ISO 9001 and 14001 REGISTERED
This product is subject to the following operating requirements
and the Life and Safety Critical Application Sales Policy:
Refer to: http://www.murata-ps.com/requirements/
ACA-20RM Series
True-RMS-AC Ammeters with Built-in CT
MPM_ACA-20RM.C01 Page 5 of 5
MECHANICAL SPECIFICATIONS
MECHANICAL DIMENSIONS: Inches (mm)
TOLERANCES: 2 PL DEC ±0.02 (±0.51)
3 PL DEC ±0.010 (±0.254)
&2/.46)%7
"!#+6)%7
3)$%6)%7
-
-
2.100
(53.34)
1.400
(35.56)
0.250
(6.35)
,%!$%$30,)4#/2%#4-/$%,3
1.024
(26.01)
0.551
(14.00)
0.984
(24.99)
1.575
(40.00)
0.480
(12.19)
0.40
(10.2)
Diameter
Lead Length
5.0 (127.0) min.
&2/.46)%7
"!#+6)%7
3)$%6)%7
-
-
2.100
(53.34)
1.400
(35.56
)
0.250
(6.35)
,%!$%$#4-/$%,3
0.480
(12.19)
0.35
(8.9)
Diameter
Lead Length
2.0 (50.5) min.
&2/.46)%7
"!#+6)%7
3)$%6)%7
0#"/!2$-/5.4%$#4-/$%,3
-
-
TB1
L1
CAL
2.100
(53.34)
1.750
(44.45)
0.250
(6.35) 1.00 (2.54)
For 2A and 20A
Models
0.26 (6.6)
Diameter
1. Description of safety marks:
Caution, risk of electrical shock
Caution, risk of danger
Equipment is protected throughout by double or reinforced insulation
2. Cleaning Instructions: Gently clean with dry cloth only.
3. Caution: if the equipment is used in a manner not specifi ed by Murata Power Solutions, the protection provided by the equipment may be impaired.
