When NEC states maximum transformer secondary OCPD size, such as the table 450.3, does it mean the size of the main OCPD in the panel that the transformer feeds? In which case the OCPD protects the secondary ONLY against the overload. Is there any secondary OCPD that can protect the secondary conductors against short circuit or ground fault?
Transformer 2ndary OCPD
- Thread starter unsaint33
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kwired
Electron manager
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- NE Nebraska
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- EC
Is usually impractical to provide overcurrent protection "at the secondary" or even within the secondary and the reason we have 240.21(C) that gives us some allowances depending on conditions. Yes we basically are only giving overload protection to the secondary conductors as well as the secondary itself and not short circuit/ground fault protection however primary protection should still open under short circuit or ground fault conditions. How fast it trips may vary depending on conditions, if a secondary coil faults to ground only a couple turns from an end that is grounded, it may not draw that much fault current and may not trip very quickly or even at all.
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