Okay, let's break down each scenario and analyze it against the NEC (National Electrical Code). Remember that the NEC is not a law, but a model code adopted by many jurisdictions. Your local codes might have amendments. This analysis is based on the 2023 NEC. Always consult with your local electrical inspector for final approval.Scenario 1: GEC partially run with SE Conductors (1) 600 MCM Cu per phase and neutral with (1) 1/0 Cu GEC in a 4" conduit from the SEB to a 400A service switch. Then, a separate 1/0 Cu GEC runs from the 400A service switch to the grounding collector bus. Question: Would it be a violation to run the 1/0 Cu GEC in the same conduit as the service conductors? Analysis

No, this is not necessarily a violation, provided the 1/0 Cu GEC is properly sized for the service conductors and serves as the sole GEC from the service equipment to the grounding electrode. The NEC encourages running the GEC with the service conductors.

NEC 250.64(E) Installation to Electrode(s). _The grounding electrode conductor shall be installed in one continuous length without a splice or joint, unless spliced only by irreversible compression-type connectors listed as grounding and bonding equipment or by the exothermic welding process. _ Exception: This permits splitting the GEC only for connection to multiple grounding electrodes. NEC 250.64(F) Installation of the Grounding Electrode Conductor. If exposed, a grounding electrode conductor or its enclosure shall be securely fastened to the surface on which it is carried... Important Considerations



GEC Sizing

The 1/0 Cu GEC must be sized correctly based on the size of the service entrance conductors (600 MCM Cu). You'll need to refer to NEC Table 250.66. For 600 MCM Cu, a 1/0 Cu GEC is likely adequate, but

always verify using the table. Continuous Length

The key here is that the 1/0 Cu GEC is effectively acting as a single GEC system from the service equipment (SEB) to the grounding electrode. The section from the SEB to the service switch and the section from the service switch to the grounding collector bus must add up to be a single GEC path.

Electrode Connection

The grounding collector bus must be connected to the grounding electrode(s) per NEC 250.50.

Scenario 2: 400A Service Tapped from 4000A Switchboard with No Separate GEC 4000A service switchboard. A 3/0 Cu GEC to the grounding collector bus. A tap section feeds a 400A service switch using (1) 600 MCM Cu per phase and neutral with a 1/0 Cu GEC in a 4" conduit. The 1/0 Cu GEC is connected to the ground bus inside the 4000A switchboard. There is no additional GEC from the 400A service switch to the grounding collector bus. Question: Is this setup acceptable per code? Analysis

This is likely a code violation. Here's why:

250.24(A)(5) Load-Side Equipment. Equipment grounding conductors shall be installed with circuit conductors run from the service equipment to all separate buildings or structures. Where a service is installed in a separate building or structure, the equipment grounding conductor shall comply with 250.
32. This section specifies how we deal with separately derived systems. While the wording doesn't exactly fit this situation, the intent is that the downstream structure has to be grounded appropriately. Indirect Connection

You're relying on the path through the ground bus inside the 4000A switchboard to the 3/0 Cu GEC as the sole grounding path for the 400A service. While the NEC allows for equipment grounding conductors to be connected to the ground bus in a panelboard, that ground bus itself needs to be properly grounded. The path from the 400A service switch's ground bus back to the 3/0 GEC is not explicitly listed to be adequate to handle the grounding of the service.

Sizing Considerations

Even if this was conceptually allowed, the 3/0 Cu GEC might not be adequate for both the 4000A service and the 400A service tapped from it.

Therefore, the GEC needs to be run directly from the service equipment to the grounding electrode.Scenario 3: 400A Service Tapped from 4000A Switchboard WITH a Separate GEC Same scenario as Question 2, but with an additional 1/0 Cu GEC run from the 400A service switch to the grounding collector bus. Question: Would this be code-compliant as well? Analysis

This is generally code-compliant,

provided the 1/0 Cu GEC is properly sized (as determined in Scenario 1) based on the service entrance conductors (600 MCM). Direct Connection

By running a separate 1/0 Cu GEC from the 400A service switch directly to the grounding collector bus, you're providing a dedicated grounding path for that service. This ensures that the 400A service is properly grounded, independent of the grounding of the 4000A switchboard.

250.24(A)(1) requires that the neutral conductor be connected to a grounding electrode at each service, and that connection is to be of sufficient size per 250.66 In this case, you will also need to size the service GEC from the 4000A panel to ensure that it is able to ground the entire service. If the service is significantly larger than the 400A subfeed, you may need to upsize the 3/0 Cu GEC going to the grounding electrode.

Key Takeaways and Recommendations



Consult Local Inspector

Always, always consult with your local electrical inspector before implementing any of these scenarios. They have the final authority on code compliance in your jurisdiction.

GEC Sizing is Critical

Pay close attention to NEC Table 250.66 to ensure the GEC is sized correctly for the service entrance conductors. Undersized GECs are a common violation.

Continuous Length

Emphasize a single, continuous GEC path from the service equipment to the grounding electrode, minimizing splices and joints.

Separate GEC for Subfeeds

When tapping services like in scenarios 2 and 3, it's generally best practice to run a separate GEC for the subfeed to ensure proper grounding. It is also best practice to keep the service conductors away from other conductors.

Disclaimer: This information is for educational purposes only and should not be substituted for the guidance of a qualified electrician or electrical engineer. Always consult with qualified professionals before undertaking any electrical work. Flag for review