You've hit on a crucial and potentially dangerous point with your corner-grounded delta system. Here's a breakdown of why what you're doing is likely incorrect and what the NEC requires.

The Problem with Tying EGCs and GEC at the Unit Under Test (UUT)

You're essentially creating a direct parallel path for neutral current (or in this case, fault current) to flow through the equipment grounding conductors (EGCs). This is exactly what you're trying to avoid in a properly grounded electrical system. Here's why it's bad:

Increased Risk of Shock

Even under normal (non-fault) conditions, there can be small voltage differences between different points in a grounding system. By forcing fault current through the EGCs, you elevate the voltage potential on the enclosures and chassis of equipment connected to those EGCs. This increases the risk of electric shock to anyone touching the equipment.

Increased Risk of Fire

EGCs are sized for fault currents. Continuously carrying current (even small amounts) can cause them to overheat, particularly at connections.

Compromised Equipment Protection

The purpose of EGCs is to provide a low-impedance path back to the source during a fault, allowing overcurrent protection devices (circuit breakers or fuses) to quickly trip and clear the fault. If the EGC is already carrying significant current, it compromises this function and slows down the response time.

Why You're Doing It (Probably) & Why It's Wrong

The likely reason you're doing this is to try and create a "reference" for the sensitive electronics in your power distribution units. The devices are "dinging" because they're seeing voltage fluctuations relative to their internal ground. However, the solution isn't to create a dangerous grounding scheme.

The Correct Way to Implement a Corner-Grounded Delta System (Based on NEC)

Here's the approach based on the NEC and common best practices:1.

Corner Grounding at the Source (Transformer)

This is absolutely crucial. One phase of the delta is intentionally connected to the grounding electrode conductor (GEC) system at the transformer serving the delta. This GEC goes to a ground rod or other suitable grounding electrode system as defined in NEC Article 250.2.

Grounding Electrode System (GES)

The GEC connects the grounded phase to a robust grounding electrode system, which is defined in NEC Article 250. This includes ground rods, building steel (if properly connected), and other methods described in the code.
3.

Equipment Grounding Conductors (EGCs)

From the source, run separate EGCs along with the circuit conductors to each receptacle or piece of equipment you're powering. These EGCs are bonded to the metal enclosures of equipment, conduit, and other non-current-carrying metallic parts.4.

EGC Termination

The EGCs from each branch circuit

terminate at the service equipment of the building and are bonded to the service neutral (in this case grounded phase).5. Neutral-Ground Bond (Your Main Disconnect)

The main neutral-ground bond occurs

only at the service entrance (the first point of disconnect for the building). This is where the neutral (grounded phase) is bonded to the grounding electrode system (GEC).

Diagram AnalysisDiagram 1 (Likely Incorrect)

Tying the EGCs and GEC at the UUT receptacle is creating a parallel neutral/fault current path. This is incorrect and dangerous. You are also creating a grounding loop which can introduce noise into the system.

Diagram 2 (Likely Correct)

Corner ground the delta with the GEC which is bonded to the EGCs at the first means of disconnect in the facility. The GEC is tied to the corner grounded phase (neutral in this case), and all of the EGCs lead back to the first means of disconnect and are terminated in the appropriate bussing or terminations in that equipment. This keeps the neutral/fault current off of the EGCs.

Recommendations


Immediate Action

Disconnect the bond between the EGC and the GEC at your UUT as it exists in your lab. This is a potentially dangerous condition.2.

Verify Corner Grounding at the Source

Make absolutely sure that one phase of the delta is properly connected to the GEC at the transformer or service equipment that supplies it. This is the foundation of the entire system. Have a qualified electrician confirm this. If this doesn't exist, you need to implement it correctly.3.

Separate EGCs

Ensure that the EGCs are run with the circuit conductors and connected to the metal enclosures of all equipment, all the way back to the service equipment.4.

One Neutral-Ground Bond

Only one point in the entire system should have a bond between the grounded phase (neutral) and the grounding system, and that's at the service entrance.5.

Address the Eaton PDU Sensitivity

Once you have the grounding system corrected, you may still have issues with the Eaton PDUs. Investigate if there is a way to adjust the sensitivity of the fault detection in the Eaton PDUs. Consult Eaton's documentation and technical support. They may have recommendations for corner-grounded delta systems. Another option is to use isolation transformers at the input of the PDUs. Isolation transformers create a new, isolated neutral/ground reference for the PDU.6.

Professional Inspection

Have a qualified and licensed electrician thoroughly inspect your entire electrical system, especially the corner-grounded delta portion, to ensure it meets NEC requirements and is safe.

Moving to the New Facility

This is the perfect* time to correct any grounding issues. Before you even hook up your equipment, ensure the grounding system in the new facility is compliant with the NEC. Engage a qualified electrician early in the process.

Legal Disclaimer:

This information is for general understanding only and should not be used to make decisions about your electrical system. Always consult with a qualified and licensed electrician for all electrical work. Failure to do so can result in serious injury, death, or property damage. Flag for review