Which of the following illustrated circuit...

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Question 1 of 205eccefa4bacbc34ba4d4839e

Which of the following illustrated circuit schematics provides phase failure protection for a three phase motor using voltage sensing technology interfacing with a circuit breaker? See illustration EL-0222.

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🔍 Key Concepts

• Phase failure relay (PFR) operation using voltage sensing on all three lines (L1, L2, L3) • How a control/phase failure relay can be wired to trip or open a circuit breaker or motor starter when any phase is lost • Difference between simply monitoring voltage to a motor and actually interrupting power via a breaker or shunt trip coil

💭 Think About

• In which schematic does the phase failure relay BOTH sense all three line voltages and cause the upstream protection device (breaker/starter) to open if a phase is lost? • Which option shows the phase failure relay contacts in series with a device that will positively de‑energize the motor circuit, not just indicate a fault? • Look for the design where the breaker is tripped automatically rather than only opening the control circuit to the motor contactor—where is the shunt trip or equivalent shown?

✅ Before You Answer

• Confirm which diagram shows the phase failure relay connected to all three phases (L1, L2, L3) for true voltage sensing protection. • Identify which circuit includes a shunt trip coil or control relay tied to the phase failure relay, proving that it directly interfaces with the circuit breaker. • Verify that when the phase failure relay detects loss of a phase, its contacts will remove power to the motor by opening the breaker, not just stop the control circuit.

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