3-Wire, 240V Single-Phase Power Measurements
Precautions and limitations applicable to 3-wire, single-phase wiring
confi gurations:
1. The ACM20’s VOLTS reading will always be that of leg L1 (120Vac), and not
the full 240Vac supply. The voltage of leg L1 is used for all power and power
factor calculations. Therefore, any voltage imbalances between legs L1 and
L2 will introduce WATTS reading errors, with the magnitude of these errors
being proportional to the voltage imbalance. In most applications, voltage
imbalance errors are usually relatively low. However, imbalance errors are in
addition to those specifi ed in the ACM20 data sheet’s “Performance/Func-
tional Specifi cations” section.
2. Due to the unique nature of this wiring confi guration, Murata Power Solu-
tions cannot guarantee that the ACM20 will meet all of its standard published
specifi cations.
IMPORTANT: the sum of the currents fl owing through the
ACM20’s built-in CT cannot exceed the ratings for that particular model’s
input range.
For example, when using the 100A model in this confi guration,
the sum of the currents in legs L1 and L2 cannot exceed 100 Amps.
3. The 100 Amp model (ACM20-4-AC1-R-C) should be used for this confi gu-
ration because of its higher current rating and ability to display power in
Kilowatts. This particular model is rated for 100A, but has an overcurrent
capability of 150A.
4. Fusing the ACM20's TB1 input lines is always required; complete fusing
specifi cations and instructions are included in the ACM20 product data
sheet. For reference, a link to the ACM20 data sheet is provided here:
http://www.murata-ps.com/data/meters/acm20.pdf
.
5. The products described in this application note are subject to Murata Power
Solutions’ “Operating Requirements” and the “Life and Safety Critical Applica-
tions Sales Policy” described at
http://www.murata-ps.com/requirements
.
6. Any mechanical or electrical modifi cations to the ACM20 (adding CT lead
extensions, use of substitute hardware or components, etc.), or failure to ad-
here to the data sheet’s specifi cations and instructions, will void its warranty
and safety-agency certifi cation status.
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.
© 2013 Murata Power Solutions, Inc.
www.murata-ps.com/support
Murata Power Solutions, Inc.
11 Cabot Boulevard, Mansfi eld, MA 02048-1151 U.S.A.
ISO 9001 and 14001 REGISTERED
www.murata-ps.com
DMS APPLICATION NOTE
23
DMS_AN_23_AppNote
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