You've accurately summarized 300.11(B) and its limitations on supporting raceways from other raceways. Let's break down why this is the case and why it sometimes comes up

Why 300.11(B) is So Restrictive:
Safety and Structural Integrity

The primary concern is safety. The original raceway was designed to carry its intended load. Adding additional load from other raceways or equipment can overstress the system. This can lead to:

Mechanical Failure

Conduits can sag, break, or detach, creating hazardous conditions.

Electrical Failure

Stress can damage conductors, leading to shorts, ground faults, or fires.

Vibration Issues

Added weight can exacerbate vibration, loosening fittings and causing wear on conductors.

Responsibility and Accountability

If an electrical problem arises, determining whose raceway is causing the issue becomes difficult if multiple systems are interconnected.

Code Compliance

It makes it difficult to ensure the supporting raceway still meets its original code-specified requirements (e.g., spacing, support intervals, securement).

Why Some People Might Want to Support from Existing Raceways



Convenience

It's often faster and cheaper in the short term to piggyback off an existing raceway rather than installing a new support system. Drilling, anchoring, and installing dedicated supports takes time and materials.

Limited Space

In densely packed areas (e.g., industrial facilities, older buildings with minimal service space), finding room for new supports can be challenging. The temptation to utilize existing infrastructure is strong.

Lack of Awareness

Some electricians might not be fully aware of the code restrictions or the potential consequences of overloading existing systems.

Where Does it End, When the System Collapses?

This is a very valid and important point. The risk of a cascade failure increases exponentially with each unsupported addition. The original raceway was never designed for that extra load. A failure in the supporting raceway then impacts everything it's supporting, leading to a potentially dangerous and costly situation.

Practical Implications Planning is Key

Proper planning during the design phase is critical. Adequate support systems should be included from the outset.

Dedicated Support is Preferred

Whenever possible, use dedicated support systems (strut, hangers, unistrut, etc.) for all raceways and equipment.

Communicate with Others

It's important to communicate the code requirements and risks of unauthorized support with other trades and personnel.*

Document Everything

When working with existing systems, thoroughly document the changes you make, including any modifications to support structures.

In Summary

While the temptation to use existing raceways for support might arise due to convenience or space constraints, 300.11(B) is restrictive for very good reasons. The risks of compromising safety, structural integrity, and code compliance far outweigh any perceived benefits. Stick to dedicated support systems and follow the code to ensure a safe and reliable electrical installation. Flag for review