The National Electrical Code (NEC) generally requires a grounding electrode system at each service.Here's a breakdown of the requirements and common practices

NEC Requirements:
250.24(A)(1) Grounding Electrode System Required. A grounding electrode system as described in Part III of Article 250 shall be installed at each service. 250.53(A)(2) Supplemental Electrode Required. A single rod, pipe, or plate electrode shall be supplemented by an additional electrode of a type specified in 250.52(A)(2) through 250.52(A)(8), unless that single rod, pipe, or plate electrode has a resistance to earth of 25 ohms or less. In short, 2 ground rods are typically required.

Specific Answer to your question

Yes, typically you will need a

minimum of two ground rods for each service in a duplex with separate meters and service disconnects.

Important Considerations and Clarifications



Resistance to Ground

The NEC allows for a single rod, pipe, or plate electrode if you can demonstrate that its resistance to ground is 25 ohms or less. This is usually tested with a ground resistance meter. Testing to 25 ohms or less is rarely done in residential and you will see 2 ground rods more commonly.

Other Electrodes (250.52(A)(2) through 250.52(A)(8))

You might be able to use other types of grounding electrodes as part of your grounding electrode system. These include: Metal Water Pipe (with specific requirements) Metal Frame of the Building Concrete-Encased Electrode (Ufer Ground) Ground RingIf you have one of these electrodes available, you may not need two ground rods. For example, if you have a metal water pipe that meets the NEC requirements for use as a grounding electrode, you may only need a single supplemental ground rod.

Local Codes

Always check with your local electrical inspector or building department. Local codes can amend or add to the NEC. They may have specific requirements regarding grounding electrode systems.

In summary:

Unless you can prove a single rod has a resistance to ground of 25 ohms or less (which is unlikely without testing) or have another acceptable grounding electrode available, you will need at least two ground rods for each meter/service disconnect in your duplex. Confirm this with your local AHJ (Authority Having Jurisdiction). Flag for review