Mike Dolt Enterprises
Mike Dolt Enterprises
User: ggunn, Location: Austin, TX, USA
Asked on: Thursday, March 27, 2025 at 12:22 pm EDT
Answered on: Thursday, March 27, 2025 at 12:22 pm EDT
Question: Scenario:A client requested assistance from a consulting engineer on a project connecting 480/277V inverters to a 208/120V service. The engineer recommended using a 208V delta to 480/277V wye transformer. The client instead bought and installed a 208/120V wye to 480V delta transformer. The client is lucky because he is using SE inverters which can connect to a 480V delta service, and he does not want to replace the (large, expensive, and probably not returnable) transformer with the recommended one.The client installed the transformer with the neutral connected back to the service from the transformer primary. The engineer advised the client to remove the neutral connection to the service, making the transformer essentially delta-delta. The client did so, but in the process the engineer saw that the client had also bonded the transformer primary neutral to ground, connecting the neutral and ground conductors between the service and the transformer in parallel, which is a clear code violation.The question:The client has removed the neutral connection between the service and the transformer primary, but the otherwise floating primary neutral is still connected to ground; is this a problem?Aside:The system was inspected and green tagged by the POCO, despite that the transformer is not the same as the one on the sealed planset, there are numerous discrepancies in wiring, and the code violation.
Yes, the fact that the otherwise floating primary neutral of the 208/120V wye to 480V delta transformer is still connected to ground is a problem, and a potentially dangerous one. Here's why: Creates a Ground Loop
Connecting the neutral to ground at the transformer primary creates a parallel path for neutral current to flow back to the service. Neutral current will divide itself between the neutral conductor and the ground conductor, potentially overloading the ground conductor, or creating elevated neutral voltage on the ground conductor.
Potential for Dangerous Voltage on Ground
This situation can cause objectionable current to flow through the grounding system, and even create dangerous voltage potential on equipment grounding conductors. Anyone touching grounded equipment could be exposed to voltage from the neutral, creating a shock hazard.
Code Violation (NEC)
As previously stated, this configuration violates the National Electrical Code (NEC). Specifically, it violates sections prohibiting parallel paths for neutral current and requiring only one point of connection for the neutral to ground, at the service entrance.
Increased Risk of Ground Faults
The dual path for neutral current can mask ground faults and make it difficult for overcurrent protective devices to properly clear faults. It may also lead to nuisance tripping of ground fault protection.
In summary, even though the neutral wire between the service and transformer primary has been disconnected, the grounded primary neutral still creates a dangerous situation. The connection between the primary neutral and ground must be removed.Recommendations for the Engineer
Document the Issue Clearly
The engineer needs to thoroughly document the incorrect installation and the associated risks, in writing, to the client. This protects the engineer from liability should problems arise later.2.
Strongly Advise Correction
The engineer should strongly advise the client to correct the grounding issue immediately. The engineer may need to escalate the concern and have a frank conversation with the client about liability issues.3.
Consider Refusing to Certify the System (If Applicable)
If the engineer is responsible for certifying the system, they should refuse to do so until the grounding issue is resolved.4.
Suggest Consulting Another Expert
It might be wise to bring in another experienced electrical engineer or consultant to review the entire system, given the numerous discrepancies observed. This provides an independent check and can help identify any other potential problems.5.
Encourage Re-inspection
While the system passed the POCO inspection, that doesn't necessarily mean it's safe or code-compliant. Encourage the client to request a re-inspection by a qualified inspector, or contact the POCO to notify them of the potential hazard.6.
Verify Inverter Compatibility: Double-check the inverter manufacturer's specifications to ensure the SE inverters are truly compatible with a 480V delta service. While the client thinks they are compatible, it's important to verify independently.The POCO's "green tag" is concerning, but it does not relieve the client or the engineer of their responsibility to ensure a safe and code-compliant installation. It's possible the inspector missed the issue, or misunderstood the configuration. It's better to be safe than sorry when it comes to electrical safety. Flag for review