Okay, let's break down the use of Erickson couplings (also known as conduit unions) with rigid galvanized steel (RGS) conduit 90-degree bends outdoors.

Understanding Erickson Couplings/Conduit Unions Purpose

Erickson couplings are primarily used to join sections of rigid conduit when you cannot easily rotate either conduit section. This typically happens when one or both ends are fixed, preventing you from threading a coupling or elbow onto them. They provide a mechanical and electrical connection without requiring rotation.

Construction

They consist of two halves that clamp together, typically with a threaded ring that tightens to secure the connection.

When are Erickson Couplings Needed for RGS 90s Outdoors? Not Always Required

They are not automatically required for every 90-degree bend in RGS conduit.

The Key Factor: Rotational Access

The determining factor is whether you can freely rotate either the conduit section or the 90-degree elbow itself to thread them together.

Why You Sometimes Can't "Spin On" an Elbow Fixed Conduit

As you experienced, if the conduit run is fixed on both ends or is otherwise secured in a way that prevents rotation, you cannot thread an elbow onto the end of the conduit. This is the most common reason for needing an Erickson.

Obstructions

Obstacles near the conduit run (walls, equipment, etc.) might physically prevent you from rotating the elbow enough to fully thread it on.

Tight Spaces

Working in confined areas can make it difficult to get the necessary leverage to rotate either the conduit or the elbow.

Length of run

if it is a long run the pipe can become slightly bowed between the points it is secured to a structure.

What Determines When You Can Spin On an Elbow? Free Rotation

If you have enough slack in the conduit run or if the conduit is only supported on one end, you can usually rotate either the conduit or the elbow sufficiently to thread them together.

Accessibility

If there are no obstructions preventing rotation.

Proper Planning

Sometimes, you can plan your conduit run to ensure you have a free end to work with at the 90-degree bend.

Example Scenario

Imagine running conduit along a wall, and then you need a 90 to go up a different wall. If the conduit is securely attached to the first wall, you likely cannot spin the elbow onto the end of the conduit. In this case, you would:1. Cut the conduit at the desired 90-degree location.
2. Thread a short nipple into the 90-degree elbow.3. Use an Erickson coupling to connect the conduit running along the wall to the nipple on the elbow.

At Every 90 You Can't Spin On? Generally Yes, if you can't spin on an elbow, an Erickson (or another type of conduit union) is required to join the sections. There might be rare exceptions where you could disassemble a large section of conduit, make the connection, and then reassemble, but that's usually far more work than using an Erickson.

Important Considerations NEC (National Electrical Code)

Ensure your installation complies with the NEC. The NEC generally allows the use of conduit unions like Ericksons. However, pay attention to grounding requirements when using them (make sure they provide a reliable ground path).

Grounding

It is very important to make sure the Erickson coupling is installed properly to ensure the conduit system is properly grounded.*

Corrosion

When using Ericksons outdoors, use ones that are rated for outdoor use and made of compatible materials (e.g., galvanized steel) to prevent corrosion.

In summary: Ericksons are valuable when you cannot thread an elbow onto a fixed section of rigid conduit. Assess each situation based on whether you have rotational access. Proper planning and understanding these principles will make your conduit installations much smoother. Flag for review