Code Change Summary: New code language was added to address specific equipment installed inside enclosures for switches and overcurrent devices.

For quite some time, Section 312.8 has allowed conductors, splices, and taps to be installed inside enclosures for switches and overcurrent devices such as cabinets containing a panelboard. Obviously, conductors must be installed inside a panelboard enclosure in order to terminate on the associated branch circuit overcurrent device. Other conductors, splices and taps inside a panelboard enclosure can occur for many reasons.

Some installations will have feed through conductors that simply pass through the panelboard enclosure and never actually terminate inside the enclosure. Other times a panelboard enclosure may contain feeder or busbar taps which are quite common in PV installations. Sometimes conductors inside a panelboard enclosure can be spliced together, no different than inside a junction box. As long as the rules in 312.8 are followed, additional conductors, splices, and taps are permitted within the panelboard enclosure.

In the 2017 NEC^®, new language was added to address power monitoring equipment which is commonly installed inside enclosures containing overcurrent devices. Before the code change, the NEC^® remained mostly silent when it came to installing such devices inside a cabinet that also contained fuses or breakers.

Now, if installing power monitoring equipment inside a switch enclosure or other overcurrent device enclosure, the power monitoring equipment must be identified as a field installable accessory as part of the listed equipment, or must be a listed kit, evaluated for field installation in switch or overcurrent device enclosures. As well, the total area of all conductors, splices, taps, and equipment at any cross section of the wiring space cannot exceed 75 percent of the cross-sectional area of that space.

Below is a preview of Article 312. See the actual NEC^® text at NFPA.ORG for the complete code section. Once there, click on their link to free access to the 2017 NEC^® edition of NFPA 70.