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110.26 Clearance for Manufactured Equipment

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    110.26 Clearance for Manufactured Equipment

    I had a customer ask a question and I'm not sure whether the NEC 110.26 applies or not. This is a manufactured (skid mounted) piece of equipment with PLC and VFD control panels. Do the clearances of 110.26 apply to this type of equipment/installation? Here are some details:[LIST][*]It's skid mounted, but not portable as it is hard plumbed and hard wired.[*]It is served by a typical 20-amp, 3-phase circuit (208 to 480), connected to an on-board door-lockout handle and internal overload protection.[*]Due to the door lockout, only the incoming power terminals can be energized if the control panel door is opened.[*]Except for external sensors, everything is pre-fabricated and self contained.[/LIST]

    It seems to me that the VFD and/or PLC is "likely to require examination, adjustment, servicing, or maintenance while energized".

    It is all but inevitable with that kind of equipment, even if it is just to adjust a parameter from the keypad on the front of the door.


      Thanks. The key word there (and 110.26) is "While Energized". That is why I mentioned the interlocking service disconnect handle that prevents the door from being opened when energized.

      Another piece of information: It's actually 2 small enclosures stacked up. The lower enclosure has the main disconnect and VFD. The upper enclosure (with a separate door) only has line voltage going to the DC power supply and a 24V AC transformer. Everything else is 24V AC or DC. The upper enclosure can be opened when energized, but the lower enclosure will cut power to the whole system when opened.

      The actual clearance isn't so much my concern. I'm mainly wondering whether 110.26 applies to a self-contained system or not.


        Are you asking whether the skid needs to be mounted in a location that leaves 36 (or 42) inches of clearance? If so, my answer is yes. That is because there is access to live line voltage in the upper enclosure.

        Or are you instead asking whether the equipment manufacturer was required to ensure that no part of the skid and no component within the skid lies within the 36 (or 42) inch of clear space? As an example, suppose the lower enclosure stuck out more than 6 inches further than the upper enclosure. Are you asking whether the manufacturer had already violated 110.26 before the equipment was even delivered to the site? If that is your question, I am not certain how I would respond. My inclination is to say that the equipment is listed as an assembly, and therefore the NEC does not apply to it at all.
        Charles E. Beck, P.E., Seattle
        Comments based on 2017 NEC unless otherwise noted.