You've described a common and frustrating situation! Let's break down the problem and explore some solutions. You're dealing with three key challenges:1. Securing the LB

The transition from buried PVC to rigid at the LB, complicated by the expansion coupling and siding/foundation interface.2.

Supporting the Rigid Nipple

Ensuring the rigid nipple passing through the rim joist is properly secured, especially considering the FMC transition inside offers no support.3.

Finding the Right Clamp

The quest for a clamp designed for rigid conduit passing perpendicularly through dimensional lumber.Here's a multi-pronged approach to tackle these issues:

1. Securing the LB and PVC Transition



Foundation Attachment (Strongest Option)

If your foundation extends slightly above grade, consider attaching directly to the concrete. Use concrete anchors (Tapcons or similar) and a

strut channel (Unistrut) vertically. This provides a rigid backbone. Clamp the LB to the strut using a standard conduit clamp and strut channel hardware. You can even notch the siding slightly, if needed, to allow the strut to sit flush against the foundation. This is the most secure solution. Siding Attachment (With Caution)

If attaching to siding, find a stud or framing member behind the siding. Use long screws that penetrate through the siding and into the framing. Again, a strut channel behind the LB is ideal for distributing the load and providing multiple attachment points. You may need to use shims to compensate for the siding profile and keep the LB level.

Avoid over-tightening screws into siding, as this can crush it and lead to water intrusion. A backing plate or a thick washer under the screw head can help prevent this. Ground Rod/Earth Support (Supplemental)

Drive a ground rod a foot or two away from the LB and use a conduit clamp (specifically a ground rod clamp, which is heavier duty than a regular conduit clamp) to the PVC below the expansion coupling, and the LB to secure them. This doesn't substitute for the foundation or framing attachment, but provides extra stability against movement, especially when pulling wire.

Consider Liquidtight Flexible Metal Conduit (LFMC) outside

As an alternative to rigid for the short section through the wall, consider using LFMC. This would allow more flexibility and reduce the need for such rigid support. It still needs to be properly supported but is more forgiving than rigid. You would then transition to EMT inside.

Expansion Coupling Placement

Ensure the expansion coupling is properly installed and has enough room to function. It's there to protect the conduit from ground movement, so make sure it's not constricted.

2. Supporting the Rigid Nipple Inside the Rim Joist

This is where finding the right clamp is key. You're right, there isn't a readily available "off the shelf" clamp specifically for rigid perpendicular to lumber. Here's how to approach it:

Modified Conduit Clamps

The closest option is to modify standard conduit clamps. You'll need to get creative.

Two-Hole Straps

Take standard two-hole straps for rigid conduit. Bend one of the "ears" on each strap to a 90-degree angle. This creates a "foot" that can be screwed to the rim joist. You'll need two of these, one on each side of the nipple. You might need to use a vice and hammer to get a clean, strong bend. Ensure you use screws long enough to bite well into the rim joist.

One-Hole Straps with Blocks

Use one-hole straps for rigid conduit. Cut two small blocks of wood (e.g., 2x4 scraps). Place a block of wood on each side of the nipple against the rim joist. Secure the blocks to the rim joist with screws. Then, use the one-hole straps to clamp the rigid nipple to the blocks. This provides a larger surface area for support.

Custom Brackets (Fabrication)

If you're handy with metalworking, you could fabricate a custom bracket from steel or aluminum. A simple L-shaped bracket with a hole for the conduit and flanges for screwing to the rim joist could work well.

Conduit Hangers

Use an adjustable pipe clamp. (aka clevis hanger) Clevis Hangers are typically used for supporting pipe from the ceiling, but could be modified by bolting to a wooden cleat to the rim joist.

Minis (Cable Support)

Use "Mini" supports. The minis can be mounted to the rim joist and will support the conduit.

Through-Bolting (Extreme Case)

If all else fails, consider a through-bolt. Drill a hole through the rim joist slightly larger than the rigid nipple. Use large washers and locknuts on both sides of the rim joist to secure the nipple. This is a more drastic measure and requires careful consideration of the rim joist's structural integrity.

Consider a Chase Nipple Instead

If the nipple is less than 12 inches long you can use a chase nipple on each side of the wall/rim joist. This will require cutting threads on the end of your conduit.

3. FMC and EMT Transition



Minimize FMC Length

As you mentioned, the FMC provides minimal support. Keep it as short as possible (ideally under 12 inches).

Support the EMT

Ensure the EMT conduit run after the FMC is properly supported with appropriate EMT straps at intervals specified by code (typically every 10 feet, and within 3 feet of boxes/fittings).

Support the transition

The transition from rigid to FMC needs to be supported. You can use a clamp around the outside of the rigid conduit to the rim joist and then strap the FMC to the same clamp.

Important Considerations



Local Codes

Always consult and adhere to your local electrical codes. The above suggestions are general guidelines, and specific requirements may vary.

Inspection

When in doubt, consult with a licensed electrician. They can assess the situation and provide specific recommendations that meet code and ensure safety. This is especially important for buried conduit and electrical work.

Grounding

Ensure proper grounding throughout the entire conduit system. This is critical for safety.*

Waterproofing

Pay close attention to waterproofing the penetration through the siding and rim joist. Use sealant (e.g., silicone caulk) to prevent water from entering the house.

In summary, the best solution will likely involve a combination of techniques: Strong support at the LB (preferably to the foundation), a creative clamp solution for the rigid nipple inside, and a short, well-supported FMC/EMT transition. Good luck! Flag for review