Technical FAQs

Ask a Question

Does Square D offer plenum rated transformers? What transformers can be used in a drop ceiling that is used for environmental air?

This is a long answer -- please read the entire response so as to completely understand the subject.

There is no such thing as a ``plenum rated transformer.`` It is not possible to build.
Per 1999 NEC article 300-22(b) ``Equipment and devices shall be permitted within such ducts or plenum chambers only if necessary for their direct action upon, or sensing of, the contained air.``
Since transformers do not do either of these, they are not allowed in ducts or plenum chambers.

A drop ceiling is not a plenum chamber, though it may be used for environmental air.
Per 1999 NEC article 300-22(c) which applies to ``... space used for environmental air-handling purposes other than ducts and plenums...`` and 300-22(c)(2) ``Electrical equipment with a metal enclosure,... and associated wiring material suitable for the ambient temperature shall be permitted to be installed in such other space unless prohibited elsewhere...`` it is apparent that some transformers can be placed in drop ceilings being used for environmental air.
To complete this, 1999 NEC 450-13 which addresses dry-type transformer accessibility comes into play. 1999 NEC 450-13(b) states ``Hollow Space Installations`` to which a drop ceiling would apply, ``Dry-type transformers 600 volts, nominal, or less and not exceeding 50 kVA shall be permitted in hollow spaces...``.
Please refer to the current NEC Code for a complete review, and, as always, local codes and the ruling of the AHJ take precedence.

CTA-ID : 11811
Was this helpful?
What can we do to improve the information ?