You're right, using stranded wire in moving or vibrating equipment is a very common practice and often a requirement. While I can't point you to a single, universally applicable article or regulation (codes vary by jurisdiction and industry), here's a breakdown of why and where you'll find this information

Why Stranded Wire for Moving/Vibrating Equipment?
Flexibility

Stranded wire is much more flexible than solid wire. This is the primary reason. Solid wire, when repeatedly bent or flexed, work hardens and becomes brittle. It will eventually fatigue and break. Stranded wire, because it's composed of many smaller wires, distributes the bending stress across these individual strands, greatly increasing its fatigue life.

Vibration Resistance

Vibration causes similar stress as flexing. Solid wire can't handle the constant motion and will break.

Prevention of Shorts/Failures

A broken conductor can create a short circuit, causing equipment malfunction, fire hazards, or even electrical shock.

Longevity

The use of stranded wire in these applications extends the life of the wiring and the equipment as a whole.

Where You'll Find Relevant Information


National Electrical Code (NEC)

While the NEC doesn't explicitly say "you MUST use stranded wire for everything that moves," it implies it through its regulations regarding conductor sizing and application based on ampacity and temperature. It also states what it cannot be used for. You will need to look at your local regulations for specific requirements2.

Industry-Specific Standards

Many industries have their own specific standards that dictate wiring practices. Examples:

Automotive Industry

SAE (Society of Automotive Engineers) standards dictate the types and sizes of wire used in vehicles, nearly always requiring stranded wire.

Aerospace Industry

Very stringent standards exist regarding wire types and installation practices in aircraft, with stranded wire being the norm.

Manufacturing/Industrial Automation

Standards for machinery, robotics, and automated systems often specify stranded wire.

Marine Industry

ABYC (American Boat & Yacht Council) standards mandate stranded wire for most applications on boats due to vibration and flexing.3.

Equipment Manufacturer's Instructions

The equipment manufacturer always has the final say. Their instructions will specify the proper wiring types and sizes for their product. Violating those instructions can void the warranty and create a safety hazard.4.

Engineering Best Practices

Experienced electrical engineers and technicians understand the importance of stranded wire in dynamic applications. They will typically specify it in designs and installations based on their knowledge and experience.5.

UL Standards

UL (Underwriters Laboratories) standards often specify the type of wire used in equipment they test and certify. This often includes requiring stranded wire for certain applications.6.

Local Electrical Codes

State and local electrical codes often amend the NEC, and these amendments might include more specific requirements for stranded wire in certain applications.7.

NFPA 79: Electrical Standard for Industrial Machinery

This standard provides detailed requirements for electrical systems on industrial machinery, including the use of stranded wire.

Keywords to Search For

"Flexible wire" "Stranded wire vibration resistance" "Wiring for moving equipment" "Fatigue life of conductors" "NEC conductor types" "ABYC marine wiring" "SAE automotive wiring" "NFPA 79"

In summary: While there isn't one single "smoking gun" article, the practice of using stranded wire in moving or vibrating equipment is a well-established and widely accepted best practice, often backed by industry standards and local codes. Always consult the equipment manufacturer's instructions and local regulations to ensure compliance and safety. Flag for review