30 C.F.R. § 18.24
Electrical clearances
Minimum clearances between uninsulated electrical conductor surfaces, or between uninsulated conductor surfaces and grounded metal surfaces, within the enclosure shall be as follows:
| Phase-to-Phase Voltage (rms) | Clearances (inches) | |
|---|---|---|
| Phase-to-Phase | Phase-to-Ground or Control Circuit | |
| 0 to 250 | 0.25 | 0.25 |
| 251 to 600 | 0.28 | 0.25 |
| 601 to 1000 | 0.61 | 0.25 |
| 1001 to 2400 | 1.4 | 0.6 |
| 2401 to 4160 | 3.0 | 1.4 |