2–12 PQMII POWER QUALITY METER – INSTRUCTION MANUAL
CHAPTER 2: INSTALLATION
2.2.3 3-wire System using Two CTs
The figure below shows two methods for connecting CTs to the PQMII for a 3-wire system.
The top drawing shows the standard wiring configuration using three CTs. An alternate
wiring configuration uses only two CTs. With the two CT method, the third phase is
measured by connecting the commons from phase A and C to the phase B input on the
PQMII. This causes the phase A and phase C current to flow through the PQMII’s phase B CT
in the opposite direction, producing a current equal to the actual phase B current.
Ia + Ib + Ic = 0 for a three wire system.
Ib = – (Ia + Ic)
For the CT connections above, the
S2 SYSTEM SETUP ÖØ CURRENT/VOLTAGE CONFIGURATION ÖØ
PHASE CT WIRING ÖØ PHASE CT PRIMARY
setpoint must be set to PHASE A, B, AND C.
FIGURE 2–9: Alternate CT Connections for 3-wire System
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