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1999 NEC 450-21(b) states ``Individual dry-type transformers of more than 112.5 kVA rating shall be installed in a transformer room of fire-resistant construction. ...`` How does this apply to low voltage transformers made by Square D?

Clarification of National Electrical Code section NEC 450-21(b)
Product Line:
LV Transformers
Applies to Ventilated and Non-Ventilated SquareD/Schneider Electric Transformers with a Class 220 insulation system
Code Section NEC450-21(b) may call for clarification in some installation situations
This is not a concern to Square D low voltage dry type transformers with enclosures as we comply with 1999 NEC 450-21(b) Exception No. 2, which states ``Transformers with Class 155 or higher insulation systems and completely enclosed except for ventilating openings.``

All Square D low voltage dry type transformers utilize a Class 220 insulation system, which is higher than a Class 155.

The previous versions of code section 450-21(b) used to reference 80?C rise as the differentiation point. The intent for that was to require units with Class 150 insulation to be in the fire-rated room, and one aspect of a Class 150 insulation system transformer is a standard 80?C rise. This created unnecessary cost for those using a Watchdog 80?C rise transformer which utilizes a Class 220 insulation system. The change in the code was done to clarify the intent of this section.

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