You are correct, and the UL standard's recommendation reinforces that. Here's a breakdown of why you are likely correct and how to approach the discussion with the engineer

Why Retorquing is Generally Discouraged (and the UL Standard Supports This):
Material Creep/Yielding

When a screw is torqued correctly, it stretches slightly and creates clamping force. Over time, especially with some materials, the screw or the clamped material can undergo creep (gradual deformation) or even yield (permanent deformation). Retorquing a connection that has experienced creep or yielding can potentially overtighten it, stripping the threads or weakening the connection further.

Embedment

The surfaces of the conductor and the termination interface compress slightly when torqued initially, essentially "embedding" into each other. This seating can make it seem like the torque has loosened over time, even if it hasn't actually lost its clamping force significantly. Retorquing can crush the strands of a wire.

Potential for Damage

Retorquing can lead to overtightening, which can damage the conductors, the terminal block, or the screw itself. This can result in a loose connection, increased resistance, and a potential fire hazard.

UL's Stance

UL standards are designed to ensure safety and reliability. Their caution against retorquing (except in limited circumstances) reflects a concern about the potential for unintended consequences.

Loosening

If a termination is coming loose after a proper torque, the screw/termination block is not properly rated for the operating conditions. Vibration, temperature cycling, or improper installation practices may cause the screw to loosen prematurely.

Why the Engineer Might Disagree (and How to Counter)



Misunderstanding of the Underlying Physics

The engineer may not fully appreciate the effects of creep, yielding, and embedment on the long-term integrity of a torqued connection.

"That's How We've Always Done It"

Sometimes, people adhere to practices without understanding the reasoning behind them, leading to conflict when discussing why an alternative approach may be more appropriate.

Belief in Periodic Maintenance

Some maintenance schedules might have included retorquing as a routine procedure. While regular inspection is good, retorquing should only be performed if there's a valid reason.

How to Approach the Discussion


Reiterate the UL Standard

Emphasize the specific language of the UL standard. Quote it directly if possible. "The UL standard states that retorquing is not generally recommended and should only be done under specific circumstances, such as using 90% of the original torque setting."2.

Explain the "Why" (in Plain Language)

"When you torque a screw, it stretches a bit to create clamping force. Over time, the materials can compress or change slightly. Retorquing then forces the connection beyond its designed tension, and can cause damage." "Think of it like bending a paperclip back and forth. Each time you bend it, it gets weaker. Retorquing can be similar – it can weaken the connection over time." "UL's concern is that retorquing can lead to overtightening, which can damage the connection and create a safety hazard."3.

Ask Questions, Don't Just Accuse

Instead of saying "You're wrong," ask questions like: "What's the reasoning behind retorquing these connections? Is there a specific problem you're trying to solve?" "Are there any known issues with these connections loosening over time?" "Have we considered the potential for creep or yielding in the materials?"4.

Suggest Alternatives to Retorquing



Thorough Initial Inspection

Ensure proper torque initially.

Visual Inspection

Implement a regular visual inspection schedule to look for signs of looseness (e.g., discoloration, visible gaps).

Thermal Imaging

Use thermal imaging to detect hotspots that may indicate loose connections.

Vibration Dampening Techniques

If vibration is a concern, use lock washers or other vibration-dampening hardware.

Consider a different screw type

A screw with a larger surface area head, or with thread locking capabilities can reduce the amount of initial re-torques and need to retorque later on.5.

Escalate if Necessary (But Do It Respectfully)

If you can't reach an agreement, suggest involving another engineer or someone from quality control who understands the UL standard and the principles of bolted connections.6.

Back Up Your Claims

Be prepared to provide the specific UL standard and any other relevant documentation (e.g., engineering articles on bolted joint behavior).

In Summary:

You are on solid ground based on the UL standard's recommendations. Retorquing should be a last resort, not a routine practice. Focus on educating the engineer about the potential downsides and suggesting alternative methods for ensuring connection reliability.Disclaimer: I am an AI chatbot and cannot provide professional engineering advice. This information is for educational purposes only.* Flag for review