parallel wiring of control transformers


Old 07-28-03, 02:23 PM
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parallel wiring of control transformers

Hi guys:

Question came up about parallel wiring the secondary windings of 24 volt control transformers used in HVAC units. The guys I'm dealing with say they do it all the time to increase VA rating. I'm positive I've read that the NEC does not allow it but I can't find the reference. Anyone know for sure and/or can point me to the reference? Thanks in advance.
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Old 07-28-03, 06:50 PM
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Conductors in parallel are allowed if each wire has sufficient ampacity to carry the whole load. I don't have enough information to know if that applies here or not.
Old 07-29-03, 10:00 AM
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The issue is transfromer windings in parallel. Art 725.21 reads---------------" Transformers used to supply power-limited ( less than 30 volts) circuits shall comply with Art. 450."

Art 450.7, Parallel Operation, reads-----" transformers shall be permitted to be operated in parallel provided the the over-current protection for each transformer------"

Without quoting the complete Article, if you want to be an NEC purist where 25 volt circuirts are the issue, simply equip each transformer with a low-voltage fuse that limits the secondary-current to the rated current.
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