Industrial Machinery

Article 670 is the handshake between the NEC and NFPA 79, the electrical standard for industrial machinery. The machine builder wires the guts of the equipment to that standard and stamps a nameplate with the full-load current and short-circuit rating. My job under 670 is to read that nameplate and provide the right supply conductors, disconnect, and overcurrent to feed the machine as a single listed unit.

The nameplate is the contract. I do not try to re-derive the load from counting motors inside a machine I did not build; I take the builder's supply-circuit numbers and the short-circuit current rating and match my feeder and protection to them. That rating also tells me whether the available fault current at that spot on the floor is acceptable.

When it applies

Article 670 bridges the Code and the machine-tool world. Industrial machinery arrives with a nameplate that lists the full-load current and supply-circuit data the builder calculated, and you use that information to size the feeder conductors, the overcurrent protection, and the disconnect that serves the machine.

Common mistakes

• Recalculating the machine's internal loads instead of trusting the builder's nameplate supply data.
• Undersizing the disconnect or feeder below the marked circuit ampacity.
• Missing the short-circuit current rating the machine requires at its supply.

In the field

When a CNC lands on the floor I read the machine nameplate, size the feeder and disconnect to the marked supply data, and verify the available fault current does not exceed the machine's rating. The builder already did the internal math, so I feed it what the plate asks for.