Okay, this is a common situation that arises when dealing with older buildings and SER cable. Let's break down the code requirements and best practices for grounding in this situation.

Understanding the Problem SER Cable without a Ground

Older SER (Service Entrance Rated) aluminum cable often only had two hots and a neutral, without a dedicated grounding conductor. This was acceptable under older codes, but it's problematic by today's standards.

Subpanel Grounding Requirements

Modern electrical codes (NEC in the US) are very specific about the need for a proper equipment grounding conductor (EGC) to be run with the circuit conductors feeding a subpanel. The EGC provides a low-impedance path back to the source (the main panel) for fault currents, allowing the breaker to trip quickly and safely.

Ufer Ground (Concrete-Encased Electrode)

A properly installed Ufer ground is excellent for system grounding (connecting to the neutral at the service). However, it cannot substitute for the required equipment grounding conductor back to the main panel in a subpanel feed. The Ufer is for grounding the system and the electrical service itself, not for fault current return.

Code Requirements and Analysis

Based on the information you provided, here's how the NEC would likely apply: NEC 250.32 (Grounding Requirements for Separate Buildings or Structures)

While condos aren't technically separate buildings, the principle is similar. This section requires an equipment grounding conductor to be run with the feeder to ensure a low-impedance fault current path.

NEC 250.130(C) (Grounding Electrode Conductor for a Separately Derived System)

This section is relevant when dealing with a separately derived system. In the context of a subpanel fed from the main panel, the key point is that the grounding electrode conductor (GEC) connected to the Ufer cannot be the sole equipment grounding conductor for the subpanel.

Why the Existing Setup is Likely Non-Compliant1. Lack of Equipment Grounding Conductor

The 1/3 SER cable lacks a dedicated equipment grounding conductor.2.

Ufer Ground is Not a Substitute

The #10 bare copper conductor connected to the Ufer cannot serve as the required equipment grounding conductor for the subpanel feed. It's connected to the earth and doesn't provide the low-impedance path back to the main panel necessary for proper fault current clearing.

What You Should Have Done Run a New #8 Ground

You are correct; running a new #8 copper equipment grounding conductor from the main panel to each subpanel along with the existing SER cable would have been the most appropriate solution. The size is determined by NEC Table 250.122, which specifies the minimum size EGC based on the overcurrent protective device (100A breaker in your case).

What You Need to Do Now (Recommendations)

This is a serious safety concern and needs to be addressed. Here's a course of action:1. Document Everything

Thoroughly document the existing conditions: Photograph the wiring at the subpanels and main panel, clearly showing the absence of a grounding conductor in the SER cable and how the Ufer is connected. Note the sizes of the breakers, cable, and grounding conductor.2.

Notify Your Employer (in Writing)

Immediately inform your employer (preferably in writing via email or a formal letter) about the non-compliant grounding situation. Explain the safety risks and the code violations. Keep a copy of this communication for your records. This protects you if something goes wrong.3.

Advise Your Employer to Contact the Electrical Inspector

The best course of action is to have your employer contact the local electrical inspector to review the installation and provide guidance on the correct remediation. The inspector's word is final in these matters.4.

Proposed Solutions (Discuss with Inspector)

Here are some options to discuss with the electrical inspector:

Install a Supplemental Grounding Conductor

This is the preferred option. Run a #8 copper equipment grounding conductor from the main panel to each subpanel. This can be run inside conduit, secured to the building structure, or even run alongside the existing SER cable. Properly bond it to the main panel's grounding bus and to the subpanel's grounding bus.

Replace the SER Cable

This is the most expensive option, but it's the best way to ensure compliance with modern codes. Replace the 1/3 SER cable with a 2/2/2/8 SER cable (two hots, a neutral, and a #8 ground).

Exception (Highly Unlikely)

It might be possible to argue that the metal conduit (if applicable) is the grounding conductor. However, this requires absolute certainty that the conduit is electrically continuous and properly bonded at all points. This is rarely the case in older buildings, and relying on conduit as the sole EGC is generally discouraged. Consult with the electrical inspector before considering this option.
Important Considerations Safety First

Do not work on energized electrical equipment unless you are properly trained and equipped. This situation is potentially dangerous.

Liability

You and your employer could be held liable if a safety incident occurs due to the improper grounding.

Future Main Panel Upgrade

The fact that the main panels will be upgraded in the future is irrelevant to the current grounding deficiency. The subpanels must be properly grounded now, regardless of future plans.

In Summary

The situation as described is a code violation and a safety hazard. The existing Ufer ground cannot substitute for the required equipment grounding conductor. A #8 copper grounding conductor should have been run with the subpanel feeds. Notify your employer immediately, contact the electrical inspector, and develop a plan to correct the grounding deficiencies. Flag for review