Code Change Summary: Spare raceways are now required to be sealed.

Section 300.5 is all about underground installations. Subsection 300.5(G) provides the rules on proper sealing of underground raceways in order to avoid condensation and moisture from entering an enclosure from the raceway and making contact with live parts.

Section 300.5(G) does not apply to every type of installation. It only applies when there is a chance that moisture inside the raceway may contact live parts.

Not all raceways are arranged in a manner that moisture inside them can contact live parts. Many underground raceways stub up into the floor of an open-bottom switchgear, far below the level of live parts. On the other hand, panelboards installed in a basement may be fed from a raceway that is underground while standing outside at grade level but then penetrates the wall of the basement above the panelboard. Proper raceway sealing must be done to ensure moisture inside the raceway doesn’t make its way into the panelboard and drip onto any live parts in the enclosure. See section 225.27 for additional sealing requirements pertaining to outside branch circuits and feeders.

In the 2014 NEC^®, conduits or raceways through which moisture may contact live parts must be sealed or plugged at either or both ends. In the 2017 NEC^®, this still remains true but now the rule also applies to spare or unused raceways.

Condensation and moisture from an underground raceway can just as easily enter an enclosure whether conductors are installed in the raceway or not. As well, spare raceways are a wonderful way for rodents and other living things to make their way into a place they shouldn’t be (see image).

Below is a preview of Article 300. 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.