112 kVA Transformer in Soiled Utility Room

Q: What are the limitations to installing a 112 kVA dry-type transformer in a soiled utility room? Our local building inspector wants a shield around the transformer separating it from all other contents of the room.

A: According to the LSC, section 9.1.2 requires electrical wiring and equipment to be installed in accordance with NFPA 70 (1999 edition). However, existing installations will be permitted subject to the approval by the AHJ. Section 450-21 of NFPA 70 permits 112½ kVA (or less) dry-type transformers to be installed indoors as long as there is a minimum of 12 inches clearance from combustible materials, or a fire resistant heat-insulated barrier is installed. Transformers over 112½ kVA must be installed in a separate 1-hour fire resistant room. It appears that the transformer in question is permitted to be installed in the soiled linen room, but subject to the approval of the AHJ. If your local building inspector wants the protective fire resistant heat-insulated barrier installed, then that is his prerogative to require it. I suggest you also check with your state authorities to see if they have any further requirements.