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When do we have to use a TP circuit breaker, and when do we have to use a TPN breaker, and why? I am specifically referring to 415 VAC 3 phase, 230 VAC in single phase, 50 HZ.

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    \$\begingroup\$ I think you should consult your local Electrical Code (or a suitably-qualified electrician) for this. The legal requirements may vary in different jurisdictions. \$\endgroup\$ – Peter Bennett Dec 18 '16 at 2:32
  • \$\begingroup\$ by the way, this question would be off-topic for diy.se unless it's in a residence, which is possible in continents that use 230/415 @50Hz. \$\endgroup\$ – Harper Jan 26 '18 at 15:33
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TPN for Y (or star) is a 4 pole breaker where Neutral is not sensed but switched with the 3 phases.

The connection between ground and neutral is in many countries not allowed. Therefore TPN is used and the N also switches for these locations.

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  • \$\begingroup\$ Yes. Neutral and equipment safety ground would be isolated in any case, whether the neutral is switched or not. It's pretty universal in mains wiring that neutral and safety ground are bonded nowhere except the main service panel, and that only to give ground-faulting current a path back to source. \$\endgroup\$ – Harper Jan 26 '18 at 16:06

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