INSTALLATION INSTRUCTIONS
FOR SYMCOM’S OVERLOAD RELAY
MODEL 777-MV-FT
SymCom’s electronic overload relays are fully programmable for customized
protection with a digital readout and RS-485 communications. The 777-MV-FT
is designed for use, in conjuction with power transformers and external current
transformers, on medium voltage systems. The 777-MV-FT also has a fast linear
trip mode.
2880 North Plaza Drive, Rapid City, SD 57702 • (800) 843-8848
CONNECTIONS
1. Using the four corner tabs or the DIN rail mounting bracket, mount the
unit near the magnetic contactor. To use the DIN rail bracket,
hook the top clip first, then apply downward pressure until the lower clip
“clicks” onto the rail.
2. External current transformers must be used (see Figure No. 1 and Table
No. 1). SymCom recommends that the external CTs have terminals for
installation convenience. All CTs must be facing the same direction and all
CT secondaries must be wired identically (i.e., all “+” terminal connected
wires must enter the loop window from the same side).
3. Power input to unit may be three-phase or single-phase. Three-phase inputs
to the unit should have instrument transformers with 120 VAC secondaries,
5 VA minimum. A separate power supply potential transformer should be
used to power the contactor coil because its signal will vary as the load is
energized and de-energized.
3.1.Three-phase voltage input: 120V three-phase can be made available by
using three potential transformers in a wye-wye configuration. Reverse
phase, single-phase and unbalance protection is available when
using the wye-wye configuration shown in Figure 2a. The motor will not start
under the above voltage fault conditions. Connect the three-phase power
from the secondary of the potential transformers to “L1”, “L2” and “L3” on the
unit using a #12 - #18 AWG wire.
3.2.Three-phase voltage input: Alternatively, a three-phase voltage input may
be constructed by connecting two potential transformers in an open delta
configuration (See Figure 2b).
BE SURE POWER IS DISCONNECTED PRIOR TO INSALLATION!
FOLLOW NATIONAL, STATE, AND LOCAL CODES!
READ THESE INSTRUCTIONS ENTIRELY BEFORE INSTALLATION!
