You've asked a good question that gets to the heart of NEC requirements for grounding and bonding in building additions. Here's a breakdown of the requirements and considerations

NEC Considerations
NEC 250.50 Grounding Electrode System (GES): All grounding electrodes that are present at each building or structure served shall be bonded together to form the grounding electrode system. NEC 250.52 Concrete-Encased Electrode (Ufer Ground): This section details the requirements for a concrete-encased electrode, including its size and installation. NEC 250.32 Buildings or Structures Supplied by a Feeder(s) or Branch Circuit(s): This is where it gets nuanced for your addition. This section dictates the grounding and bonding requirements for a separate building or structure. The key here is the separate part.

Analysis for Your Situation

Because the two structures are being physically joined such that there is a continuous concrete structure and rebar, no, you are likely NOT required to install another UFER ground that is run back to the main service.

Here's why:1. Not a "Separate Building or Structure"

The NEC 250.32 is focused on separate buildings or structures. Since your new addition is physically attached and the rebar is tied together, it's treated, electrically, as an extension of the existing structure. You effectively have one large building now.2.

Existing UFER Adequacy

The existing UFER ground already serves the entire concrete and rebar structure because the rebar is continuous. The rebar provides an excellent bonding path.3.

Bonding via Rebar

The tying together of the rebar creates a solid electrical connection between the existing structure and the addition. This means that the new addition is, in essence, bonded to the existing UFER ground through the continuous rebar network.

Important Considerations and Recommendations Verify Rebar Connection

Crucially, you must ensure that the rebar tying method provides a reliable electrical connection. Typically, this is achieved by overlapping the rebar and securely tying it with steel tie wire at multiple points along the overlap. Welding is an even better connection, but may need to be done by certified welders. The local AHJ might have specific requirements.

Supplemental Grounding Electrode (May be beneficial but likely not required)

While not strictly required in your situation, a supplemental grounding electrode (ground rod, ground plate, or ground ring) at the addition might be beneficial, especially if the soil conditions are different or if you're concerned about lightning protection. However, it's critical that any supplemental electrode is bonded to the rebar network (and thus to the existing UFER ground). This ensures proper equipotential bonding.

Grounding Electrode Conductor (GEC) Sizing

Verify that the existing grounding electrode conductor (GEC) from the main service to the UFER ground is adequately sized for the increased load and size of the expanded structure. The sizing is based on the size of the service entrance conductors (NEC 250.66).

Grounding Bus in New Electrical Panels

Ensure that all new electrical panels in the addition have a proper grounding bus bar that is bonded to the rebar network. This is typically done by connecting a grounding conductor from the panel's grounding bus to the rebar.

Local AHJ (Authority Having Jurisdiction) is Key



The most important step is to discuss your plan with the local electrical inspector (AHJ). They have the final say on what is acceptable in your jurisdiction. They may have specific interpretations of the NEC or local amendments that you need to follow. Provide them with the details of the construction, the rebar tying method, and your proposed grounding and bonding plan. Get their approval before you pour the concrete. Documentation

Document everything thoroughly. Keep records of the rebar tying method, the grounding electrode system, and any discussions you have with the AHJ.

In summary: Based on your description, you likely do not* need a separate UFER ground for the addition. The key is the continuous rebar network creating a solid bond to the existing UFER. However, verifying the rebar connection, ensuring adequate GEC sizing, bonding the new panels, and (most importantly) consulting with the AHJ are essential. Flag for review