Page 8 of 27 MCM-Inst-1.10
The figure above shows all possible connections for an MCM84, including both Modbus RTU and
Modbus TCP, even though both will not be present on a single MCM. The line voltage connections
in the lower-right are factory wired to the circuit protection, and the 5 Vdc connections are factory
wired to the power supply. Models of the MCM with fewer circuits follow similar layouts but with fewer
modules. Each MCM ships with a connection diagram affixed inside the front door.
The connection diagram shows the position (CT1, CT2, CT3) and polarity (white, black) of each
current transformer input.
3.1 Installation Record
The MCM is provided with an installation record to plan and document the installation. The first page
documents general information: model number, serial number, electrical service, Modbus settings,
RS-485 settings, Ethernet settings, etc. The additional pages of meter and CT schedule document
each load and current transformer input to the MCM.
It is essential to document the loads and CT
configurations because the meter must be correctly programmed to match the actual installa-
tion.
To download additional copies, see
https://ctlsys.com/support/mcm-installation-record/
The meter and CT schedule contains several columns of information. The electrician or installer
should fill in most of these columns, but the integrator will typically fill in the
MeterConfig
. See below
for an example schedule.
Channels:
The MCM is composed of one or more modules (PCBs), each with 12 CT inputs (chan-
nels). The channels column shows one block for each set of 12 channels. The numbering, 1-12,
13-24, etc., is just informational and will not be used when accessing data from the MCM.
Submeter Block:
As described above, the MCM is composed of four or more SMBs, each behaving
like a WattNode meter with three CT inputs. Each SMB has its own Modbus address, based on
the address (ADDR) set with the DIP switch on the primary SMB. For example, if you set the DIP
switch address to 2, then ADDR+0 = 2, so the address of the primary SMB will be 2.
Modbus Addr:
The Modbus address field is filled in by hand, by adding the DIP switch address to the
offset documented in the SMB column. For example, if the DIP switch address is 2 and the subme-
ter block shows ADDR+3, then fill in the Modbus address as 5.
CT#:
Each SMB has three CT inputs. This column shows the CT numbers printed on MCM boards
and on the wiring diagram.
Panel:
You may use the panel column to identify the panelboard or circuit breaker panel. Be sure to
use this column if you are metering more than one panel with a single MCM.
Ckt#:
Use this column to record the circuit number within the panelboard. These are the numbers
printed adjacent to circuit breakers and on the panel schedule.
CT Amps:
It is important to record the rated amperage of each current transformer. In many cases,
the CT amps will match the circuit breaker rating, but this is not always true.
L1, L2, or L3:
Use this column to record the line voltage phase associated with this current trans-
former. You may refer to the phases as L1, L2, L3 or as ØA, ØB, ØC.
MeterConfig:
The integrator will normally configure the
MeterConfig
registers and fill in this column.
The
MeterConfig
value depends on whether a CT input is associated with L1, L2, or L3, and
whether the CT measures a line-to-neutral or a line-to-line load.
Load Name/Description:
Fill in this column to document the load for each MCM input.
