Okay, let's clarify the grounding bushing requirements for your situation.

Understanding the Basics Purpose of Grounding Bushings

Grounding bushings (or grounding wedges/hubs) are used to provide a reliable, low-impedance path to ground for metal raceways (like EMT) that contain circuit conductors. This is crucial for safety:

Fault Current

If a fault occurs (a wire comes loose and touches the metal conduit), the fault current needs a way to return to the source and trip the overcurrent protection (circuit breaker) quickly.

Electromagnetic Interference (EMI)

Grounding the conduit can also help reduce EMI.

Key NEC Sections

The most relevant sections in the National Electrical Code (NEC) are Article 250 (Grounding and Bonding) and Article 300 (Wiring Methods).

Where Grounding Bushings Are Required

The core requirement is to ensure the metal raceway (EMT) is effectively grounded at both ends to create that low-impedance fault current path. Here's a breakdown: Service Equipment

At the service equipment (the 3000A MDP in your case), the EMT must be bonded to the service grounding electrode system. This is typically accomplished through listed grounding locknuts or bushings (with a bonding jumper if necessary), or through the enclosure itself if it's properly listed and designed for grounding.

Separately Derived Systems (Subpanels)

At the subpanels, the EMT must be bonded to the grounding electrode system of that separately derived system. This is done to ensure the fault current has a low impedance path back to the source.

Long Runs

Even in between the service equipment and the subpanels, if the EMT run is very long, intermediate bonding might be needed. This is less common in typical subpanel setups, but it's something to consider for extremely long runs.

Specific Answer to Your Question: Bushings on Both Ends?Yes, grounding bushings are generally required on BOTH ends of the 2" EMT runs connecting the 3000A MDP to the three 200A subpanels.Here's why


Effective Grounding Path

You want to ensure the EMT is grounded at both the source (3000A MDP) and the destination (200A subpanels). This provides a reliable, low-impedance path for fault current regardless of where the fault occurs within the EMT system.2.

NEC 250.96 (Bonding Other Enclosures)

This section generally requires metal raceways (like EMT) to be bonded to enclosures. Grounding bushings or suitable alternatives accomplish this.3.

NEC 250.92(B) (Methods of Bonding at the Service)

While this specifically refers to service equipment, the principle applies. Effective bonding is crucial at all points in the grounding system.

How to Properly Ground/Bond the EMT

Here's how to ensure proper grounding and bonding in your situation:1. At the 3000A MDP



Grounding Locknuts/Bushings

Use listed grounding locknuts or grounding bushings where the EMT connects to the MDP enclosure. These have a setscrew to tighten onto the EMT, providing a secure mechanical and electrical connection.

Bonding Jumper (if necessary)

If the enclosure is not designed for grounding, you may need to use a grounding bushing with a bonding jumper connected to the MDP's grounding busbar. Check the MDP's labeling and instructions to see what's required.2.

At the 200A Subpanels



Grounding Bushings

Use listed grounding bushings on the EMT where it enters the subpanel enclosure.

Bonding Jumper

Attach a bonding jumper from the grounding bushing to the subpanel's ground bar (where all the equipment grounding conductors terminate). The size of this jumper is determined by NEC Table 250.102(C)(1) (or 250.66 if it's part of the service).

Check Subpanel Instructions

Consult the subpanel's instructions. Some panels might have specific requirements or pre-tapped holes for grounding connections.

Important Considerations and Best Practices Listed Equipment

Use only UL-listed grounding bushings, locknuts, and connectors.

Tight Connections

Ensure all connections are tight and free of corrosion.

Clean Surfaces

Make sure the EMT and enclosure surfaces are clean and free of paint or coatings where the grounding connections are made. This ensures good electrical contact.

Inspection

Have your work inspected by a qualified electrical inspector to ensure compliance with the NEC and local codes.

Local Amendments

Be aware that local jurisdictions can amend the NEC. Always check with your local authority having jurisdiction (AHJ) to confirm specific requirements in your area.

Concentric Knockouts

When using concentric or eccentric knockouts, you must use a grounding bushing, a listed grounding locknut, or similar device to ensure a solid ground connection. Do not rely on the knockout rings alone for grounding.*

PVC Coating: If you are using Rigid Metal Conduit (RMC) that is PVC coated, ensure that you are using a PVC coated grounding bushing at both ends.

In summary, while you might get by in some situations with only grounding the EMT at one end, it's best practice and generally required by code to ground BOTH ends to ensure a safe and reliable electrical system. Flag for review