User manual 09/2009 - Schneider Electric

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User manual 09/2009 - Schneider Electric

The Protection FunctionNeutral ProtectionPresentationNeutral protection on Micrologic 5 and 6 trip units is adapted to protecting all types of electrical distributionapplications against overload and short-circuit currents.It is available on:• 4-pole trip units• on the 3-pole trip units with ENCT optionIt is identical for Micrologic 5 and 6 trip units.DescriptionThe neutral conductor (if it is distributed and identical to the phases in size: i.e. full neutral) is normallyprotected by the phase protection.The neutral must have specific protection if:• It is reduced in size compared to the phases• Non-linear loads generating third order harmonics (or multiples thereof) are installedIt may be necessary to switch off the neutral for operational reasons (multiple source diagram) or safetyreasons (working with power off).To summarize, the neutral conductor can be:• Non-distributed (3-pole circuit breaker)• Distributed, not switched off and not protected (3-pole circuit breaker)• distributed, not switched off but protected (3-pole circuit breaker with ENCT option)• Distributed, switched off and protected (4-pole circuit breaker)Compact NSX trip units are suitable for all protection types.Compact NSX Possible Types Neutral Protection3-pole circuit breaker 3P, 3D None3-pole circuit breaker with ENCT option 3P, 3D None3P, 3D + N/2 Half neutral3P, 3D + N Full neutral3P, 3D + OSN Oversized neutral4-Pole Circuit Breaker 4P, 3D None4P, 3D + N/2 Half neutral4P, 4D Full neutral4P, 4D + OSN Oversized neutralP: Pole; D: Trip unit; N: Neutral protection48 LV434104 09/2009

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