[Arash]

When and why are the four pole circuit breakers used as outgoing feeder in switchgears?

When and why are the four pole circuit breakers used as outgoing feeder in switchgears?

موضوع

[Hamid]

Generally the decision about neutral breaking depends on the way of earthing system execution. The neutral must be broken by a multi-pole device: – In TT and TN, if neutral cross-section is less than phase cross-section. – In terminal distribution in view of the Neutral/Phase reversal risk. The neutral must be protected and broken: – In IT for intervention of the protection device on the double fault, with one of the faults possibly on the neutral; – In TT and TN-S if neutral cross-section is less than phase cross-section For all earthing systems if the installation generates harmonic currents of rank 3 and multiples (especially if neutral cross-section is reduced). In TN-C the neutral, which is also the PE, cannot be broken which is dangerous as a result of its potential variations, due to load currents and insulation fault currents. To prevent risks, a local equipotentiality and an earth connection must be provided for each zone/consumer. For details of various earthing system you can refer to IEC 60364 and below figures:

[نویسنده]

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