1. Grounding electrode system
For a 200A disconnect, the NEC specifies that you must establish a grounding electrode system, as outlined in Article 250.50. This system typically uses one or more grounding electrodes, such as ground rods, a metal water pipe, or concrete-encased rebar (often called a Ufer ground). Using multiple types of electrodes can improve grounding reliability, especially when dealing with varied soil conditions.
2. Sizing the grounding electrode conductor
The NEC provides strict guidelines on grounding electrode conductor size based on the service entrance conductor size. For a 200A service disconnect, most installations use 2/0 copper or 4/0 aluminum for service conductors. As a result, the grounding electrode conductor size will typically be 4 AWG copper or 2 AWG aluminum, based on NEC Table 250.66. Of course, there are exceptions and smaller conductors are allowed in certain situations. For example, 6 AWG copper can be used for rod, pipe, or plate electrodes and 4 AWG copper for concrete-encased electrodes. These requirements ensure that the grounding system can handle potential fault currents safely, reducing risk to both equipment and personnel.
3. Bonding requirements
Bonding is a critical element of grounding, ensuring that all metal parts within the installation are securely connected to the grounding electrode system. This requirement means that the disconnect enclosure itself must be bonded, as well as any metal conduit or other metal components. By bonding these components, you prevent potential differences in voltage that could pose shock hazards. While NEC 250.50 pertains to rules for grounding electrode systems, requirements for the bonding of service equipment enclosures, other enclosures, and piping systems can be found in NEC 250.90, 250.92, 250.96, and 250.104.
4. Additional electrodes
If a single ground rod doesn’t provide sufficient grounding resistance (less than 25 ohms), NEC 250.53(A)(2) requires the addition of a second rod, spaced at least 6 feet away from the first. This helps to ensure adequate grounding in areas with soil that has high resistance, like sandy or rocky locations. This practice not only aligns with code requirements but also enhances overall safety and reliability.
5. Connection to water pipes
Where available, an underground metal water pipe can also serve as a grounding electrode. However, the NEC mandates that if a water pipe is used, it must be supplemented with an additional electrode, such as a ground rod or concrete-encased rebar, to maintain grounding integrity. This requirement helps ensure a robust system, even if the water piping is updated or replaced with non-conductive materials over time.
6. Neutral and ground separation
A key distinction here is whether your 200A disconnect serves as the main service disconnect or a downstream disconnect. For a main service disconnect, the NEC requires bonding the neutral to the ground. However, for a downstream disconnect, the neutral and ground must remain separate, which helps prevent ground loops and other electrical issues.