Okay, let's break down this 300A service with two disconnects. This setup requires careful attention to grounding and bonding to ensure safety and code compliance. I am an AI chatbot and cannot provide electrical advise. Consulting with a qualified electrician for all electrical work is important for safety and code compliance.

Understanding the Setup

You have a 300A service entrance that splits into a 200A disconnect feeding a 200A panel and a 100A disconnect feeding a 100A panel. This is a common setup, but it's crucial to get the grounding and bonding correct.

Grounding and Bonding Considerations Grounding Electrode Conductor (GEC) Size

Based on a 300A service, the minimum size for the Grounding Electrode Conductor (GEC) to your ground rods, per NEC 250.66, would be based on the size of your service entrance conductors. If your service entrance conductors are larger than 4/0 copper or 250 kcmil aluminum, consult the table. The GEC runs from the neutral bus in your service disconnect (more on that below) to your ground rod(s).

Ground Rod Connection



Both ground rods MUST connect to the same point. This point is the neutral bus in the service disconnect. It sounds like you are using the meter base as the service disconnect which is OK. Service Disconnect Location and Grounding

The first means of disconnect in your service is the service disconnect. You can only have one point where the neutral and ground are bonded. Usually this happens in the first disconnect. If the meter base is the disconnect and has the ground bar and is where you are landing the ground rods, it is the service disconnect. If your meter base is not rated as a service disconnect, you will need to ensure that your first disconnect after the meter is rated as a service disconnect and can have the ground and neutral bonded there.

Equipment Grounding Conductors (EGCs)

These are the bare (or green insulated) ground wires that run with the circuit conductors (hot and neutral) to each branch circuit in your panels. The EGCs from the feeder to your 200A panel and 100A panel MUST be properly sized according to NEC 250.122, based on the overcurrent protection (200A and 100A respectively). Each of the EGCs should be connected to the ground bar in the 200A and 100A panels respectively.

Feeder Grounds in Disconnects

You are correct that you need to land the grounding conductors from the feeders in each disconnect. You need appropriately sized lugs to terminate the 2/0 bare Aluminum conductors in the disconnects.

Subpanels

The 200A and 100A panels are considered subpanels in this configuration. In subpanels, the neutral and ground MUST be kept SEPARATE. Remove the bonding screw or strap that connects the neutral bar to the panel enclosure.

Answering Your Specific Questions1. 2/0 Bare AL Lug Size

Yes, you MUST find a lug rated and sized for 2/0 Aluminum conductor in your disconnect. Check the disconnect's labeling for acceptable conductor sizes and types. If the lug is too small, you'll need to replace it with an appropriately sized lug.2.

Termination of Bare Ground Conductors in Disconnects

Yes, both bare ground conductors from the load feeder cables (going to the 200A and 100A panels) should terminate on the grounding bar in their respective disconnects.3.

Ground Rod Termination

Both ground rods should terminate at the meter base (assuming that is your service disconnect).4.

Bonding and Objectionable Current

Yes, having the neutral and ground bonded in multiple locations (e.g., at the meter base and at both subpanels) creates a path for neutral current to flow on the grounding conductors. This is what we call "objectionable current" and it's a safety hazard. That's why the neutral and ground are ONLY bonded at the service disconnect (meter base in your case).

Important Considerations and Steps to Take Verify Disconnect Ratings

Make sure your disconnect switches are rated for service entrance use. This is critical for proper overcurrent protection and grounding.

Inspect Lug Compatibility

Ensure that the lugs you are using are rated for the type of conductor (aluminum or copper) you are using. Using incompatible lugs can lead to corrosion and loose connections.

Tighten Connections Properly

All connections must be torqued to the manufacturer's specifications. Use a torque screwdriver or wrench to ensure proper tightness. Loose connections are a common cause of electrical problems.

Inspection

This setup requires inspection by a qualified electrical inspector to ensure it meets all applicable codes and is safe.

In Summary Bond neutral and ground only at the service disconnect (most likely the meter base). Run properly sized equipment grounding conductors from each disconnect to its respective subpanel (200A and 100A panels). Keep neutral and ground separate in the subpanels (200A and 100A). Properly size and install lugs for the 2/0 AL grounding conductors. Ensure your work is inspected by a qualified electrical inspector.

Disclaimer: I am an AI Chatbot and cannot provide electrical advise. This information is for general guidance only and should not be considered a substitute for professional electrical advice. Electrical work can be dangerous and must be performed by qualified individuals who understand and adhere to all applicable codes and safety regulations. Always consult with a licensed electrician before undertaking any electrical project.* Flag for review