Code Change Summary: New code definition of a “messenger or messenger wire”.

For many NEC^® code cycles, messenger wires were mentioned in many articles but never defined in Article 100.

In the 2020 NEC^®, a messenger wire is defined as a wire that is run along with or integral with a cable or conductor to provide mechanical support for the cable or conductor.

Messenger wires are often used when hanging overhead luminaires or festoon lighting.

An example is found in Article 336 which covers Power and Control Tray Cable (Type TC) which is normally installed in a cable tray. Section 336.10 specifies how TC cable is permitted to be used and one permissible option is to use TC cable in outdoor locations where supported by a messenger wire.

The new definition is a step in the right direction but still leaves a gray area as to what is considered acceptable to be used as a messenger wire. Can a copper conductor be used? How about a steel aircraft cable? What gauge of messenger wire is acceptable?

Many of the above questions are expected to be answered in a product’s installation instructions if a messenger wire is chosen as a way to provide mechanical support for the cable or conductor.

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.