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Pad Mounted Transformer Clearance Requirements
Clearance is set by the serving utility and by NESC, and it is a common reason a job fails inspection after everything else is right. The widely used figures are ten feet in front of the doors, three feet at the sides and rear, and ten feet from building openings and combustible walls. Your utility governs, so get their standard in writing early.
The commonly required clearances
| Direction | Typical requirement |
|---|---|
| Front, the door side | 10 feet clear working space |
| Sides and rear | 3 feet |
| To building openings | 10 feet from doors, windows and air intakes |
| To combustible walls | 10 feet, or a fire barrier |
| Overhead | Clear for crane placement and future replacement |
These are the figures most utilities use, and they are not a substitute for your serving utility's own standard. Get that standard in writing before the pad location is fixed. Moving a transformer after it is set is expensive and slow.
The one people forget
Vehicle protection. If the unit sits anywhere a truck can reach it, bollards are usually required, and that changes the pad layout. Decide it at design, not at inspection.
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