X-Ray Equipment

Article 660 handles equipment with a very peculiar demand profile: a huge current pulse during the exposure and almost nothing between shots. It relies on the manufacturer's momentary and long-time rating figures to size conductors and overcurrent, and it requires clear disconnecting means and solid grounding given the high voltages inside the generator.

I lean hard on the equipment data for these, because guessing at an X-ray supply is a good way to get either nuisance trips during exposures or an undersized feeder. And with the internal high voltage and the medical setting, careful grounding is not optional. I coordinate closely with the imaging vendor on every install.

When it applies

Article 660 governs the electrical side of X-ray equipment, whether it is a dental unit, a hospital imaging system, or industrial inspection gear. These machines draw a brief, very high momentary current during an exposure, so the circuit and disconnect rules account for that pulse rather than a steady load.

Common mistakes

• Sizing the branch circuit to the momentary current when the Code lets you use the long-time rating for feeders, or vice versa. Know which current applies where.
• Omitting a readily accessible disconnect within sight of the equipment.
• Neglecting the grounding of the high-voltage components and the machine frame.

In the field

Wiring an imaging suite, I learned the whole design hinges on that split between the momentary exposure current and the continuous draw. The feeder can be sized on the long-time rating because the exposure is a fraction of a second, but the disconnect and grounding still have to handle the real machine. Read the nameplate carefully; these units publish both numbers precisely because the Code uses them differently.