In my experience, one of the trouble spots in project specifications is coordinating the control panels furnished with mechanical equipment with the standards that apply to the balance of electrical equipment on the project. Regardless of what you may include about NEMA enclosure types, short-circuit ratings, and other features, manufacturers tend to supply their standard control panel. The result is often an installation that cannot be verified to meet code or project requirements.

The National Electrical Code (NEC) states that unmodified internal wiring of equipment does not require inspection at the time of installation if it has been listed by a qualified electrical testing laboratory (sometimes referred to as a Nationally Recognized Testing Laboratory or NRTL), but not all equipment is listed. Absent a listing, the engineer and inspector may have no clear basis for acceptance or rejection of a control panel; in fact, information needed for a decision may not even be provided with the panel. The new Article 409 - Industrial Control Panels, in the 2005 edition of the NEC, addresses this issue by providing construction, protection, and labeling requirements.


Article 409 broadly defines an industrial control panel as "an assembly of two or more components such as motor controllers, overload relays, fused disconnect switches ... related control devices such as pushbutton stations, selector switches ... and similar components." It applies to factory-fabricated and field-built control panels, but it would not apply if the control panel is listed by an NRTL as part of the equipment itself, such as on an elevator or standby generator.

The construction requirements reference other NEC articles where these requirements have already been developed in detail for other types of equipment. These features include enclosure classifications (Table 430.91), wiring space at terminals (Articles 312 and 430), and grounding (Article 250). This brings industrial control panels into line with the standards applied to motor control centers, panel boards, and other equipment that they emulate.


Requirements for overcurrent (overload and short circuit) protection are consistent with those applied to motor and control circuits elsewhere in the NEC. Fuses or circuit breakers, which provide overcurrent protection, do not have to be in the control panel. However, if you intend to use the external branch circuit breaker to meet this requirement, be aware that it must be sized for the internal components and that a standard 20A breaker may be too large. In some cases, shop drawings for an equipment control panel indicate that a special type of protection, such as Class J fuse, is required ahead of the control panel. If you had assumed you could supply this panel from a standard circuit breaker, this could mean a costly change order to the electrical contractor.

To address these issues, I recommend including language similar to the following in mechanical specs: "The equipment control panel shall serve as a complete combination motor controller, fully complying with NEC Articles 409 and 430 and shall be provided with all NEC-required components including disconnecting means, control power supply, overload, short circuit and ground fault protection."


The most beneficial aspect of Article 409, in my opinion, is the requirement that each panel be marked with the following information:
  • Manufacturer's name
  • Enclosure type number
  • Supply voltage, phase, frequency, and full load current
  • Short-circuit rating
  • Suitable for use as service equipment (if applicable)
  • Wiring diagram or diagram index number

    This is intended to ensure that the inspector can determine whether the control panel meets code requirements. It should also address the problem that I've discussed in previous columns of equipment control panels having inadequate short circuit ratings for the system they are supplied from. The short-circuit rating must be that given by the NRTL if it is so listed and labeled, or must established using an approved method, such as UL-508A -2001: Industrial Control Panels Outline of Investigation.


    When specifying control panel construction complying with UL standards, you should have these requirements covered, as their standards are coordinated to ensure that UL-labeled equipment is suitable for installation under the NEC. When UL or other NRTL listing is not specified or available, you can reference the Article 409 requirements in your specification, or even better, use language such as that described above to place responsibility for compliance on the manufacturer. ES