Below are several examples in Article 250 of metal boxes and other enclosures being part of the effective ground-fault current path:

• Section 250.97 considers a metal raceway carrying a 277/480 circuit as properly bonded if it is connected to a box with listed fittings.
• Part V of Article 250 requires bonding to ensure electrical continuity and the capacity of an enclosure to conduct safely any fault current likely to be imposed on it.
• Section 250.109 allows metal enclosures, used to connect bonding jumpers or equipment grounding conductors, or both, together to become a part of an effective ground-fault current path.
• Section 250.110 requires enclosures of fixed equipment containing ungrounded conductors to be connected to an equipment grounding conductor.

In the 2020 NEC^®, Section 250.109 was added to allow metal enclosures to be considered part of an effective ground-fault current path.

The code language in 250.109 is worded carefully so as not to give the impression that a metal box or enclosure is technically an “equipment grounding conductor” since not all metal boxes or enclosures are listed as grounding and bonding equipment. Most are evaluated and listed as enclosures and not subjected to high levels of ground-fault current during the product certification process.

Below is a preview of the NEC^®. See the actual NEC^® text at NFPA.ORG for the complete code section. Once there, click on their link to free access to the 2020 NEC^® edition of NFPA 70.

2020 Code Language:

250.109 Metal Enclosures. Metal enclosures shall be permitted to be used to connect bonding jumpers or equipment grounding conductors, or both, together to become a part of an effective ground-fault current path. Metal covers and metal fittings attached to these metal enclosures shall be considered as being connected to bonding jumpers or equipment grounding conductors, or both.