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Protecting low-voltage circuits
1-3 Phase-loss protection
1-3 Phase-loss protection
1-3-1 Phase-loss fault
(1) Three-phase power supply circuit
A phase-loss fault occurs when there is a disconnection in one
of the phase wires. If a motor continues running under those
conditions, the result is an imbalance in the current flow to the
motor windings that can generate enough heat to burn out the
windings. This can develop eventually into a short-circuit or
ground fault.
A phase-loss protection device protects the motor windings
from burning and prevents the fault from developing into a
wider problem.
1-3-2 Phase-loss burnout protection
(threephase circuit)
One way to prevent phase-loss from burning the motor or
severely lowering its durability is to disconnect it from the
circuit. For economic reasons, it is recommend that this be
done using a manual motor starter (MMS) with phase-loss
protection capability.
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