Understanding The Forgotten NEC Article 404: Fixture Wires

Introduction

As an electrician, I often come across Article 404 of the National Electrical Code (NEC), which covers the installation requirements for fixture wires. However, many electricians tend to forget about or overlook this important article. In this article, I aim to provide an in-depth look at NEC Article 404 and why it's critical for electrical safety.

What are Fixture Wires?

Fixture wires are the electrical wires inside light fixtures, lamps, and other devices that connect to a power source. They include the following:

• Supply wires that bring power into the fixture from the branch circuit.
• Internal wires that connect the socket, ballast, LED driver, etc.

Fixture wires are different from the standard building wires used inside walls and conduits. They're designed for limited flexibility and light loading inside their enclosed fixtures.

Common types of fixture wires include:

• FFH-2: Fixture wire, heat-resistant, thermoplastic insulation
• RFH-2: Fixture wire, heat-resistant, crosslinked thermoset insulation
• RFHH-3: Same as above but dual-rated for both wet and dry locations

Key Requirements of NEC Article 404

NEC Article 404 lays out several rules for the proper selection and installation of fixture wires. Below are some of the key requirements:

Usage Restrictions

• Fixture wires cannot be run inside walls, conduits, plenums, etc. They're only permitted inside fixtures.
• Wires with thermoplastic insulation like FFH-2 have a 90°C temperature rating. They cannot be used where operating temperatures exceed this limit.
• Fixture wires cannot be spliced within the fixture cavity unless inside a separate enclosure like a junction box.

Size and Support

• Wires must be properly sized for the ampacity of the fixture per NEC rules.
• Wires must be supported every 12 inches and within 3 inches of each termination point.

Protection and Isolation

• Wires must be protected from physical damage both during and after installation.
• Ballasts, transformers, and LED drivers must be isolated from combustible materials.

Allowable Locations

• Fixture wires can run through dry, damp, or wet locations depending on their insulation type and rating.

Grounding and Bonding

• Fixtures must be grounded to the equipment grounding conductor.
• Non-current-carrying metal parts must be bonded.

Why Article 404 Matters for Safety

Compliance with NEC Article 404 ensures several important safety benefits:

• Prevents fire hazards: Properly sized wires reduce overheating risks. Isolation and support prevent wires from being damaged.

• Avoids electric shocks: Grounding/bonding helps prevent energized fixture parts.

• Maintains performance: Correct wire sizing maintains proper voltage to the light source.

• Enables code compliance: Adhering to Article 404 is necessary for passing electrical inspections.

Real-World Examples

Let me walk through some real-world examples of Article 404 safety principles:

Sizing Wires Correctly

I recently installed under-cabinet lighting that drew 5 amps total. The supply wires from the branch circuit were #12 AWG, rated for 20 amps.

However, the fixture wires connecting the driver to the individual pucks were only #18 AWG. This undersized wiring could overheat and cause a fire.

I had to replace with properly sized #16 AWG fixture wiring to meet both manufacturer specs and NEC rules.

Isolating Ballasts

I installed fluorescent shop lights in a garage and initially mounted the ballasts directly against the wood supports.

This went against 404.8, which prohibits ballasts in direct contact with combustible materials.

I fixed it by isolating the ballasts using steel bar hangers. Now they have the 1-inch separation from wood required by code.

Supporting Wires Properly

In retrofitting fixtures, I often find original fixture wires that are not properly supported per NEC 404.10.

For example, wires may be loosely hanging or have loose connections. This can lead to broken wires over time.

I use code-compliant supports like silicone-lined wire clips to securely fasten wires every 12”.

Conclusion

Though overlooked at times, NEC Article 404 contains important guidelines for safe fixture wiring. By following its rules on sizing, protection, isolation, locations, and support, we prevent fire and shock hazards.

As electricians, detailed knowledge of Article 404 helps us work safely and pass inspections. I hope this overview has provided a helpful understanding that we can apply in our daily work. Please leave any questions below, and I'll do my best to answer them.