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?

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Issue:
Clarification of National Electrical Code section NEC 450-21(b)

Product Line:
LV Transformers

Environment:
Applies to Ventilated and Non-Ventilated SquareD/Schneider Electric Transformers with a Class 220 insulation system

Cause:
Code Section NEC450-21(b) may call for clarification in some installation situations

Resolution:

This is not a concern to SquareD/Schneider Electric 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.``

SquareD/Scheider Electric Ventilated and Non Ventilated 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 80C rise transformer which utilizes a Class 220 insulation system. The change in the code was done to clarify the intent of this section.