Should a dual-power supply in a TN-C system use 3P or 4P?
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This post was last edited by Soy sauce PK Beer on 2017-1-10 at 21:37. A dual-power supply cabinet is needed; the incoming mains power is three-phase four-wire, which should belong to the TN-C system. Should 3P or 4P connectors be used for the dual power supply? Logically, in a three-phase four-wire system, the N wire and the PE wire are combined into one. For safety reasons, the PEN wire must not be disconnected at any time; therefore, four-pole circuit breakers are absolutely prohibited. However, systems that require dual power supply switching need to use four-pole circuit breakers in order to meet the isolation requirements during the maintenance, testing, and repair of the entire system. So, when TN-C is used with a dual power supply, should 3P or 4P circuit breakers be used?
It is said that 3P is better to use, while 4P should be used with caution. It has a significant connection to the grounding system.
Since attachments cannot be uploaded, I’ve copied it and posted it here for you to view: Selection and Application of Four-Pole Switches (5) ● Four-pole switches are strictly prohibited in TN-C systems. ● Article 461.2 of IEC60364-4 stipulates that in TN-C systems, the PEN conductor shall not be isolated or switched. ● Article 2.2.12 of GB50054-95 stipulates that in a TN-C system, the PEN conductor must not be connected to switching equipment. ● Article 4.5.6 of GB50054-95 stipulates that in a TN-C system, it is strictly prohibited to disconnect the PEN wire; no device for disconnecting the PEN wire shall be installed
In a dual-power supply system, per the specifications, the neutral points of the two transformers must be grounded at only one point; in other words, the N wires of the two transformers are connected to each other. Use a 3P switch