You're right to be concerned. The installation you describe doesn't sound like a proper implementation of NEMA 3R and certainly deviates from your specification. Let's break down NEMA 3R and why your approach with Myers hubs is generally the preferred method.

What Makes a NEMA 3R Enclosure "R"?

NEMA 3R enclosures are designed for outdoor use and provide protection against the following: Rain

This is the key differentiator. The "R" in 3R specifically addresses rain ingress.

Sleet

Protection against sleet (ice) damage and operation.

External Ice Formation

The enclosure is designed to not be damaged by the formation of ice on its exterior.

Windblown Dust and Dirt

Some level of protection against dust and dirt, though not as robust as other NEMA ratings.

Key Characteristics and Requirements for NEMA 3R



Drip Shield/Overhangs

NEMA 3R enclosures typically have drip shields or overhangs above doors, seams, and other openings to prevent rainwater from directly entering.

Gaskets

Gaskets are used around doors and covers to create a tight seal.

Drainage

They often have drainage provisions (small holes) to allow any water that does enter to escape, preventing buildup and corrosion.

Knockouts

This is where your concern lies. Knockouts are inherent points of weakness in the enclosure's weatherproof integrity. NEMA 3R enclosures are tested to meet the rain test with all unused holes and fittings properly closed.

Why Myers Hubs Are Preferred (and Often Required)

Myers hubs (or similar sealing hubs) are designed to maintain the NEMA 3R rating when conduits enter the enclosure. Here's why:

Complete Seal

They create a watertight seal around the conduit entry point. The sealing washer or O-ring on the outside of the enclosure is key to preventing water from entering.

Corrosion Protection

They prevent water from entering the knockout itself, thus protecting the metal of the enclosure from corrosion.

Compliance

Using proper sealing hubs is the accepted and expected method for maintaining the NEMA 3R rating when making conduit entries.

Problems with Using Only Sealing Locknuts on the Inside



Not Designed for External Sealing

Sealing locknuts are typically designed to seal against the inside of the enclosure. They are not primarily intended to prevent water from entering around the knockout from the outside.

Water Ingress

Rainwater can still penetrate around the knockout and potentially enter the enclosure, especially during heavy rain or wind-driven rain.

Corrosion

Water trapped between the conduit, the knockout, and the enclosure will promote corrosion, as you pointed out.

Compromised Rating

While the sealing locknut might slow water ingress, it does not provide the same level of protection as a properly installed sealing hub. Using only sealing locknuts on the inside is generally

not considered a best practice for maintaining a NEMA 3R rating, and most likely does not meet code.

Finding Installation Instructions and NEMA Standards



NEMA Website

The NEMA (National Electrical Manufacturers Association) website (nema.org) is the definitive source.

Search

Use the search function on the NEMA website for "enclosure standards" or "NEMA 250".

NEMA 250

NEMA 250 is the standard that defines enclosure types and their performance criteria. You'll likely need to purchase this standard for detailed specifications and test procedures.

Manufacturer's Instructions

Always refer to the installation instructions provided by the manufacturer of the specific NEMA 3R enclosure and the Myers hubs you are using.

UL Standards

UL (Underwriters Laboratories) also plays a role in testing and certifying enclosures. Look for UL listings on the enclosure.

AHJ

Your local Authority Having Jurisdiction (AHJ) has the final say on what is acceptable for code compliance.

Why Your Contractor's Installation is Incorrect and What to Do


Violation of Specification

The contractor failed to meet the explicit specification requiring Myers hubs. This is a breach of contract.2.

Compromised NEMA 3R Rating

Using only sealing locknuts on the inside likely compromises the enclosure's NEMA 3R rating.3.

Potential for Corrosion

This installation creates a corrosion risk.

Steps to Take


Document Everything

Take detailed photographs of the incorrect installation.2.

Communicate with the Contractor

Formally notify the contractor in writing that the installation does not meet the specification and is unacceptable. Cite the specification requirement for Myers hubs.3.

Refer to NEMA 250

Reference NEMA 250 in your communication (even if you don't have a copy) to emphasize the importance of proper enclosure integrity.4.

Involve the Engineer of Record (if applicable)

If there was an engineer involved in the project, bring this to their attention.5.

AHJ

If the contractor refuses to correct the installation, contact your local electrical inspector (AHJ). They can enforce code compliance and ensure the installation meets the required NEMA 3R rating.6.

Demand Correction

The contractor should remove the existing conduit fittings and install proper Myers hubs (or equivalent sealing hubs) with the sealing washer or O-ring on the outside* of the enclosure.7.

Consider a Punch Test

You can perform a garden hose test by spraying water on the box and conduit entry point to verify if the installation is weatherproof.

In Summary:

You are correct to be concerned about the improper installation. Sealing locknuts on the inside alone are not a substitute for proper sealing hubs for maintaining a NEMA 3R rating, and it does not meet your project specification. The contractor needs to correct the installation to comply with the specification and ensure the long-term reliability and weather resistance of the electrical system.Remember to always consult with qualified professionals and refer to applicable codes and standards. Flag for review