NEC Section 210.64(E) provides requirements for ferrous metal raceways and enclosures that contain a grounding electrode conductor. Ferrous metals contain appreciable amounts of iron such as steel and are usually magnetic. A non-ferrous metal does not have magnetic properties and includes metals such as aluminum and copper.

The general rule for ferrous metal raceways and enclosures containing a grounding electrode conductor requires them to be electrically continuous from the point of attachment to cabinets or equipment to the grounding electrode and to be securely fastened to the ground clamp or fitting.

Cable armor must also comply with this section. Cable armor is similar to armored cable type AC, but there is little space between the armor and the conductor inside. The NEC^® does not have a specific article covering cable armor. Most cable armor is made of a ferrous galvanized steel interlocking armor applied over a bare conductor (see image).

The code language requires ferrous metal raceways, enclosures, and cable armor to be bonded at each end of the raceway or enclosure to the grounding electrode or grounding electrode conductor to create an electrically parallel path. Bonding methods permitted to accomplish this include the following three methods from Section 250.92(B)(2) through (4):

• Connections using threaded couplings or listed threaded hubs on enclosures if made up wrenchtight
• Threadless couplings and connectors if made up tight for metal raceways and metal-clad cables
• Other listed devices, such as bonding-type locknuts, bushings, or bushings with bonding jumpers

There are listed fittings that are suitable to bond cable armor to the service enclosure, but many electricians select the wrong product to use on the other end when bonding cable armor to the actual grounding electrode within.

Below is a preview of Article 250. 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:

250.64(E) Raceways and Enclosures for Grounding Electrode Conductors.

(1) General. Ferrous metal raceways, enclosures, and cable armor for grounding electrode conductors shall be electrically continuous from the point of attachment to cabinets or equipment to the grounding electrode and shall be securely fastened to the ground clamp or fitting. Ferrous metal raceways, enclosures, and cable armor shall be bonded at each end of the raceway or enclosure to the grounding electrode or grounding electrode conductor to create an electrically parallel path. Nonferrous metal raceways, enclosures, and cable armor shall not be required to be electrically continuous.

(2) Methods. Bonding shall be in compliance with 250.92(B) and ensured by one of the methods in 250.92(B)(2) through (B)(4).

(3) Size. The bonding jumper for a grounding electrode conductor(s), raceway(s), enclosure(s), or cable armor shall be the same size as, or larger than, the largest enclosed grounding electrode conductor.