You've hit the nail on the head with your understanding of the "why" behind requiring RGS elbows. Let's break down the scenario and answer your question

Understanding the Specification

The specification calling for "elbows to be RGS conduit" for underground PVC installations is, as you suspect, primarily concerned with: Mechanical Protection

PVC, while durable, can be more susceptible to crushing, punctures, and damage, especially when buried and subjected to soil pressure, shifting ground, or potential digging. RGS (Rigid Galvanized Steel) conduit provides a significantly stronger and more robust physical barrier.

Pulling Tension

Large or long wire pulls generate considerable tension. PVC elbows, especially those with tight bends, can deform or even crack under high pulling forces, leading to costly repairs and re-pulling. RGS elbows are much better suited to withstand those forces.

Rodding & Future Maintenance

RGS elbows are more durable when using fish tape or cable rodding equipment for future maintenance or cable replacement.

Answering Your QuestionIs it necessary to provide these RGS elbows for 90's that remain underground (horizontal bend) and if not why?Generally, yes, it is prudent and likely necessary to follow the specification unless you have a documented reason to deviate and approval to do so.

Here's why, even for horizontal bends underground, RGS is often preferred: Specification Compliance

The specification likely doesn't explicitly differentiate between vertical and horizontal bends. "Elbows to be RGS conduit" typically means all elbows within the underground PVC system. Failing to comply would be a violation of the project documents.

Soil Pressure & Ground Movement

Even a horizontal bend is subjected to soil pressure. Over time, settling and ground movement can put stress on a PVC elbow, potentially causing it to deform or crack. RGS offers superior resistance.

Accidental Damage

While less likely than with a vertical sweep, there's still a chance of accidental damage from digging or excavation activities above the horizontal run. RGS provides better protection in such a scenario.

Pulling Considerations

Even a horizontal bend can experience significant pulling forces, particularly if the run is long or has multiple bends.

When Could Deviations Be Considered (and what you need to do)



Exceptionally Short Runs

If the run is extremely short (e.g., only a few feet) with minimal pulling tension, a PVC elbow might be acceptable if you can provide sufficient protection and if the specification allows for exceptions.

Specific Soil Conditions

If the soil is exceptionally stable and free of rocks or debris, and the trench is carefully prepared and backfilled with clean material, the risk to PVC might be reduced. However, even in these scenarios, the specification typically trumps these considerations.

Important Considerations Before Deviating



Get Clarification

Always seek clarification from the engineer, architect, or project manager responsible for the specifications in writing. Do not assume an exception is acceptable.

Provide Justification

If you believe a PVC elbow is acceptable in a particular situation, clearly document your reasoning, including details about the soil conditions, run length, pulling tension calculations, and proposed protective measures.

Obtain Approval

Do not proceed with using PVC elbows without written approval from the appropriate authority. Doing so could result in rejection of the work and costly replacement.

Consult Applicable Codes

Ensure that any deviation from the specification complies with all applicable electrical codes and regulations.

Consider Alternatives

Consider using long-radius PVC elbows if the bending radius is a concern for pulling. Although they will not address concerns regarding physical protection

In Summary:

While there might be rare situations where a PVC elbow could be acceptable for a horizontal bend in an underground PVC system, it's generally prudent to follow the specification and use RGS elbows. Deviating from the specification without proper authorization can lead to significant problems and costs. Always seek clarification, provide justification, and obtain approval before making any changes. Flag for review