Okay, I understand your situation. You're dealing with an existing installation in an apartment building with underground feeders to the individual apartments, and the apartment subpanels are currently wired with no equipment grounding conductor from the main distribution panel, but do have a GEC from the water meter to the panel. This is a common scenario in older buildings and creates a potentially dangerous situation.Here's how to think about this and what's generally required, understanding that I can't give definitive advice without a full code book (which you'll absolutely need to finalize your plans) and a complete understanding of the entire system.

Key Considerations & Potential Hazards



Lack of Equipment Grounding Conductor (EGC) on Feeders

This is the most critical issue. Without an EGC (ground wire) running with the feeder conductors from the main distribution panel to each apartment subpanel, you lack a low-impedance fault current path back to the source. In the event of a fault (e.g., a hot wire touching a metal appliance chassis), the fault current will attempt to return through other paths, often the water piping system, which is not designed for this purpose. This can lead to elevated voltages on metal parts of appliances and plumbing, creating a shock hazard.

Water Pipe as Fault Current Path

The #6 GEC to the water meter is intended to bond the water piping system to ground, which helps to equalize potential and reduce shock hazards in normal conditions. However, it is not a suitable substitute for an EGC as a fault current path. It may not be adequately sized to carry high fault currents and could itself become energized.

Separating Neutrals and Grounds

This is the correct approach for a subpanel situation, provided there is a proper EGC.
What to do (Generally)


Prioritize Establishing a Proper EGC

This is the most important step. You must establish a dedicated equipment grounding conductor from the main distribution panel to each apartment subpanel. Consider the following:

Retrofitting a Ground Wire

The ideal solution is to run a new cable or conduit that includes an EGC along with the existing feeder conductors. This may be challenging or impossible depending on the existing raceway and building structure. Consider the NEC rules allowing for retrofitting a separate EGC, especially Article 250 and 300.

Deriving a Ground

This is generally not permitted unless you have another suitable and compliant method, such as a properly sized and installed equipment grounding conductor run separately from the circuit conductors, or where you can utilize an existing metallic raceway system as the EGC (check for continuity and proper connections).

DO NOT rely on the building steel unless it's specifically designed and approved as an EGC. Exception? Double check the exceptions and language in the NEC. There may be a rare exception for existing installations that allows for other methods with certain restrictions, but this would require very careful analysis and likely wouldn't be ideal.2. Separate Neutrals and Grounds at the Subpanel

Once you have a proper EGC, this is crucial.

Isolate the Neutral Bus

Ensure the neutral bus bar in each apartment subpanel is isolated from the panel enclosure. The neutral bus should only be connected to the incoming neutral conductor from the feeder.

Connect EGC to Grounding Bus

Connect the newly installed EGC to a separate grounding bus bar that is bonded to the panel enclosure.

Connect the Water Pipe GEC to the Grounding Bus

The #6 GEC from the water meter also connects to this grounding bus bar.

Verify Bonding

Ensure the grounding bus bar is properly bonded to the metal enclosure of the subpanel.3.

Review Bonding and Grounding System at Main Distribution Panel

Make sure the grounding and bonding system at the main distribution panel is properly installed and up to code. This includes proper bonding of the neutral to ground at the service entrance and appropriate sizing of the main grounding electrode conductor.

Code References (Consult the latest NEC)



Article 250 (Grounding and Bonding)

This is the most important article. Pay close attention to:

250.24 (Grounding Service-Supplied Alternating-Current Systems)



250.30 (Grounding Separately Derived AC Systems)

Might be relevant if the building uses a transformer system.

250.32 (Grounding Requirements for Separate Buildings or Structures)

Not directly applicable since it's not a separate structure, but contains relevant concepts.

250.50 (Grounding Electrode System)



250.92 (Bonding Metal Piping and Metal Exposed Structural Metal)



250.130 (Equipment Grounding Conductor Connections)



250.134 (Equipment Fastened to Metal Surfaces)



250.146 (Use of Grounded Circuit Conductor for Grounding Equipment)



Article 300 (Wiring Methods)

Especially for retrofitting.

Article 310 (Conductors for General Wiring)

Conductor sizing for EGCs.

Article 408 (Switchboards and Panelboards)

Specific requirements for panelboard wiring.

Important Cautions



This is NOT a DIY Project

This type of electrical work is complex and potentially dangerous. It MUST be performed by a qualified, licensed electrician who is familiar with the NEC.

Inspection is Essential

Contact your local electrical inspector before starting any work. They can provide guidance and ensure the installation meets local codes.

Document Everything

Keep detailed records of the work performed, including conductor sizes, grounding electrode connections, and inspection approvals.

Safety First

Always de-energize circuits before working on them and use appropriate safety equipment.*

Load Calculations

Before adding new circuits or modifying existing ones, verify that the service and feeders have sufficient capacity to handle the load.

In summary: Your primary goal is to establish a proper equipment grounding system for the apartment subpanels. Without a dedicated EGC, the risk of electrical shock and fire hazards is significantly increased. Carefully evaluate your options for installing an EGC, separate the neutrals and grounds in the subpanels, and consult with a qualified electrician and electrical inspector to ensure a safe and code-compliant installation. Good luck, and stay safe out there! Flag for review