You're right to question the blanket statement about SSBJs. Let's break down the situation and see if they are actually required in your specific setup.

Your Setup

Utility Supply -> Customer-Owned Transformer (480/277V Wye) -> Parallel PVC Conduits -> Service Entrance Rated Switchboard Each parallel conduit contains phase conductors and a neutral.

Why SSBJs are Typically Used on Customer-Owned Transformers

The main reason for using SSBJs on customer-owned transformers is to ensure a low-impedance ground fault current path back to the source (the transformer's neutral point). This allows overcurrent protection devices (OCPDs, like breakers) to quickly clear ground faults, minimizing damage and improving safety. This is especially important when the transformer serves a service entrance.

Analyzing Your Specific Situation



Service Entrance

Your switchboard is explicitly "service entrance rated." This is a critical point. The NEC (National Electrical Code) has specific requirements for service entrances.

Parallel Conductors with Neutrals

The fact that you're running multiple parallel conductors, each containing a neutral, significantly impacts the situation. This is key.

PVC Conduit

PVC is non-conductive. It does not provide a ground fault current path. All grounding must occur within the wiring itself.

NEC Considerations & Why You Probably Don't Need SSBJs

Here's why SSBJs likely aren't necessary, assuming proper installation according to the NEC:1.

Parallel Neutrals Function as Grounding Conductors

Because each raceway contains a full-size neutral conductor, each neutral acts as its own grounding conductor, providing a low impedance path back to the transformer neutral. SSBJs are effectively achieved by your installation method in this specific case. 250.30(A)(6) Exception No. 2 specifically addresses this.
2.

Solidly Grounded Wye System

Since you have a 480/277V Wye system that is solidly grounded, the available ground fault current should be high enough to clear the OCPDs.3.

NEC 250.30(A)(6) Exception No. 2

This is the crucial section of the NEC. It states that with multiple services, a grounding electrode connection isn't necessary at the transformer if each service has its own grounding electrode system. Your parallel conductors with individual neutrals effectively create this condition. The code expects the impedance of the neutral to be sufficiently low enough to act as the grounding conductor.

Why You NEED To Carefully Consider the Following



Neutral Sizing

Ensure your neutral conductors are appropriately sized to carry the maximum unbalanced load and the expected ground fault current. Under sizing the neutrals will render this design invalid.

Bonding

You absolutely must ensure proper bonding at both the transformer and the switchboard.

Transformer

Bond the transformer's neutral to the transformer's case and to the grounding electrode conductor system. This is your main grounding connection.

Switchboard

Bond the switchboard's neutral bus to the switchboard's enclosure.

Grounding Electrode System

Make sure you have an adequate grounding electrode system at the transformer. This typically consists of a ground rod, ground ring, concrete-encased electrode (ufer), or other approved electrode. You must comply with NEC 250.50 and 250.
52.

Overcurrent Protection Coordination

Verify that your OCPDs (breakers or fuses) are properly sized and coordinated to clear ground faults quickly and effectively. A short circuit study may be required.

Local Codes and AHJ (Authority Having Jurisdiction)

This is the most important point. Always consult with your local electrical inspector (AHJ) to confirm that your design meets their specific requirements. They have the final say. Some AHJs may prefer SSBJs even if the NEC doesn't strictly require them.

In Summary

In your scenario, with parallel conductors each containing a full-size neutral, the NEC likely does not require SSBJs between the transformer and the switchboard assuming you properly size the neutral conductors, ensure adequate bonding at both ends, and have a proper grounding electrode system. The parallel neutrals act as the grounding conductors. However, it's crucial to get approval from your local AHJ before proceeding.

Recommendation


Consult with the AHJ

Discuss your design with the electrical inspector and get their approval.2.

Perform a Short Circuit and Coordination Study

This will verify that your OCPDs will clear ground faults quickly and safely.3.

Document Everything: Keep detailed records of your calculations, design decisions, and AHJ approval.Good luck with your installation! Flag for review