You've identified a common problem with PVC conduit installation: the conflict between expansion fittings and tight strapping. Here's a breakdown of what's happening and whether your approach is appropriate

The Problem:
PVC Expands and Contracts

PVC conduit changes in length significantly with temperature changes. This is a much bigger deal than with metal conduit.

Expansion Fittings are Key

Expansion fittings are designed to accommodate this movement. They allow the conduit to lengthen and shorten without putting stress on the system, which could lead to damage (cracked conduit, pulled connections, etc.).

Tight Strapping Hinders Movement

When you strap PVC conduit too tightly, you're essentially anchoring it in place. This prevents it from moving freely within the expansion fitting. The expansion fitting needs to be able to slide back and forth.

Conflict = Failure

Tight strapping negates the purpose of the expansion fitting. The conduit will push/pull against the straps instead of moving into/out of the fitting, potentially causing problems.

Your Approach (Upsized Straps)

Using slightly oversized straps is a

good idea in principle as a way to achieve the following: Allowing Movement

The slight extra space in the strap should allow the conduit to slide through the strap as it expands and contracts.

Secure Support

You still want the conduit to be supported, preventing sagging or other issues.

Important Considerations and Best Practices



Saddle Straps

These are generally preferred for PVC conduit because they provide a wider bearing surface and distribute the weight of the conduit more evenly. Avoid one-hole straps unless absolutely necessary.

One-Hole Straps

You can put a space between the conduit and the structure, but this causes the conduit to sag

Finger Tight Only

The strap should be snug enough to hold the conduit in place but loose enough to allow it to move. You should be able to easily rotate the conduit within the strap. "Finger tight" is a good guideline.

Don't Overtighten Screws

Be careful not to overtighten the screws holding the strap in place, as this can deform the conduit.

Expansion Coupling Placement

Follow manufacturer's instructions for the proper placement of expansion fittings. This usually involves calculating the expected temperature range and installing the fitting with the correct amount of travel exposed.

Strap Spacing

The NEC (National Electrical Code) and local codes dictate the maximum spacing between conduit supports. Follow these guidelines, but remember that the goal is support, not rigid fixing.

Check for Free Movement

After installing a section of conduit with an expansion fitting and straps, manually check to ensure the conduit can slide freely through the straps near the fitting.

Consider Specialized Straps

Some manufacturers offer straps specifically designed for PVC conduit that allow for thermal movement. These often have a slightly larger inner diameter or a flexible element.*

Code Compliance

Ensure your strapping method complies with local electrical codes. Some jurisdictions may have specific requirements for supporting PVC conduit.

In summary: Using slightly larger straps that allow for movement is a better approach than using tightly cinched straps. However, it's important to do it correctly: don't go overboard with the size, ensure the conduit is still adequately supported, and verify free movement. Always prioritize code compliance and best practices. Flag for review