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CHAPTER 10: MISCELLANEOUS
MM3 MOTOR MANAGER 3 – INSTRUCTION MANUAL
When setting instantaneous relays, care must be taken to ensure that the instantaneous
element does not operate during normal operating conditions such as a motor start.
Symptoms of an instantaneous element that is set too sensitive are nuisance or
intermittent tripping of the relay during energizing of the system.
Furthermore, CTs do not react predictably when a DC current is applied. The waveform
that is shown above is not necessarily the waveform that each of three phase CTs would
output. If there is a residual connection for ground fault detection, that element could
operate when asymmetrical currents are present.
ASYMMETRICAL STARTING CURRENT
10–3
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