MCM-Inst-1.10
Page 13 of 27
3.2.4 Grounded Leg Service
In rare cases with delta services or single-phase two-wire, line-to-line services, one of the phases may
be grounded. The MCM will correctly measure the voltages, power, and energy for grounded leg ser-
vices. Depending on how the
MeterConfig
registers are programmed, the measured voltage, power,
and energy for the grounded phase may be zero, and the status LEDs will not light for the grounded
phase. This type of service may result in unusual power factors.
See the web article
Corner-Grounded Delta Circuits
3.2.5 Four-Wire Delta Service
There are several names for this service type, including high-leg, wild-leg, stinger leg, or wild phase. It
is a three-phase delta service with a center-tap on one of the transformer windings to create a neutral
for single-phase loads. These occur in North America in two configurations: 120/208/240 Vac and
240/415/480 Vac.
With the MCM, this service type can be measured just like any three-phase, four-wire wye service. By
convention, you should connect the
V
B
terminal to the high leg. See the web article
for more information.
3.3 Installation Checklist
See the sections referenced below for installation details.
□
Turn off power
before making line voltage connections.
□
□
If needed, connect any external circuit protection and disconnects (see
).
□
Connect the line voltage wires (see
).
□
Mount the CTs around the line conductors. Make sure the CTs face the source (see
□
Connect the twisted white and black wires from the CTs to the black terminal blocks on the
MCM, matching the wire colors to the white and black dots on the MCM label (see
□
Document the information for each circuit (load) using the installation record. Whoever does
the commissioning with need this record (see
).
□
Connect the RS-485 output (for Modbus RTU) or the RJ45 Ethernet jack (for Modbus TCP) of
the MCM to the monitoring equipment (see
).
□
Configure the DIP switches (see
□
Check that all the wires are secure in the terminal blocks by tugging on each wire.
□
Turn on power to the MCM.
□
Configure the appropriate MCM registers (see
).
□
Verify correct operation using the LEDs or the Modbus interface (see
3.4 Mounting
The MCM is available in four NEMA rated enclosures, small and large, steel and fiberglass.
●
Protect the MCM from temperatures outside its limits. See
●
The MCM enclosure is rated for NEMA 4 (steel) or NEMA 4X (fiberglass). If you need to preserve
this rating, be sure to use fittings with the same ratings.
The MCM enclosure can weigh up to 30 pounds (14 kg), not including the weight of any connected
conduit. Mount it securely using the four holes in the mounting tabs. The steel enclosures include fixed
mounting tabs with four 5/16 inch (7.9 mm) holes, while the fiberglass enclosures use detachable
mounting tabs with four 11/32 inch (8.7 mm) holes.
