You're right to be asking about this! Proper grounding and bonding of equipment racks is crucial for safety (reducing shock hazards) and proper operation of sensitive electronic equipment. Here's a breakdown of the requirements and how it's typically achieved, focusing on the NEC (National Electrical Code) which is the primary standard in the US

Key Concepts: Grounding vs. Bonding
Grounding

Connecting electrical equipment to the earth (ground) to provide a low-impedance path for fault currents. This helps trip overcurrent protection devices (circuit breakers, fuses) quickly in the event of a fault.

Bonding

Connecting metallic parts of electrical equipment together to create an electrically conductive path. This reduces the potential voltage difference between those parts, minimizing shock hazards and creating a low-impedance path for fault current return.

NEC Sections That Apply (and where to look for updates)



Article 110. General Requirements for Electrical Installations

This article covers general requirements applicable to all electrical installations, including the need for safety and proper installation.

Article 250. Grounding and Bonding

This is the MAIN article. It's extensive, but essential. Pay close attention to:

Part III, System Grounding

Discusses grounding of electrical systems (not directly equipment racks, but foundational).

Part IV, Enclosure, Raceway, and Service Cable Grounding

Addresses grounding metal enclosures, raceways, and service cables that might be connected to the equipment rack or nearby.

Part V, Bonding



This is critical. It covers bonding methods and requirements for various types of equipment. 250.92 Bonding of Services

If your rack is near the service entrance, this section might have indirect relevance.

250.96 Bonding Other Enclosures and Raceways

This section will govern bonding of raceways that contain power to the equipment within the rack.

Part VII, Methods of Equipment Grounding

Discusses various methods used to connect equipment grounds.

Article 645. Information Technology Equipment



CRUCIAL FOR IT RACKS. This article specifically addresses the unique requirements for IT equipment, including: 645.16 Connecting Hardware and Interconnecting Cables

Describes the requirements for the connecting hardware and the data cables that interconnect the information technology equipment.

645.11 Uninterruptible Power Supplies (UPS)

Specifies the grounding requirements for UPS systems.

645.5 Supply Circuits and Interconnecting Cables

Covers power and communication cables within the IT equipment area.

Article 408. Switchboards, Switchgear, and Panelboards

If the equipment rack houses a power distribution panel, this article is relevant.

Article 400. Flexible Cords and Cables

If you're using flexible cords and cables to power equipment within the rack, be sure they are listed and approved for the application and have a grounding conductor.

Article 314. Outlet, Device, Pull, and Junction Boxes; Conduit Bodies; Fittings; and Handhole Enclosures

This covers the grounding of metallic boxes that contain electrical connections for equipment in the rack.

Specific Requirements for Equipment Racks (Derived from the NEC)


Metal Rack Structure Bonding

The metal structure of the equipment rack must be bonded together and to the electrical system ground. This provides a low-impedance path for fault currents and minimizes voltage differences between different parts of the rack. This bonding can be achieved in several ways:

Grounding Electrode Conductor (GEC)

Ideally, the rack should be bonded back to the electrical system's Grounding Electrode Conductor. The size of the GEC must be appropriate for the service size.

Equipment Grounding Conductor (EGC)

Connect the rack to the equipment grounding conductor of the branch circuit that supplies power to the rack's power distribution unit (PDU) or power strips. This is commonly done using a dedicated grounding wire or lug bolted to the rack's frame. The EGC must be sized according to NEC Table 250.122, based on the rating of the overcurrent protection device (breaker or fuse) protecting the circuit.

Metal Conduit/Raceway

If metal conduit or raceway is used to supply power to the rack, the conduit/raceway itself acts as the equipment grounding conductor, provided it is properly connected to the equipment and the electrical panel.2.

Bonding to Power Strips/PDUs

Each power strip or PDU within the rack must have its metal enclosure bonded to the rack's frame. This is usually achieved via the power strip's or PDU's grounding conductor connection and its physical mounting to the rack.3.

Grounding of Connected Equipment

Each piece of equipment (UPS, servers, switches, etc.) must have its chassis grounded. This is usually achieved through the equipment's power cord, which includes a grounding conductor. However, ensure that the grounding conductor is properly connected and that the equipment is not relying on a poor or missing ground connection.4.

Isolated Ground Receptacles (Optional, but common in IT environments)

Sometimes, "isolated ground" receptacles are used within the rack. These receptacles have their grounding conductor isolated from the conduit or box they are mounted in. The grounding conductor runs directly back to the main panel's grounding bus, minimizing noise on the ground. If used, they must be installed correctly according to NEC 250.146(D). These are typically marked with an orange triangle.

Important

Isolated ground receptacles do not eliminate the need for bonding the rack itself. The rack still needs to be bonded as described above.5.

Supplemental Bonding (Common Practice, Highly Recommended)

Even when equipment is grounded through its power cord, it's often good practice to run supplemental bonding conductors between the chassis of key equipment and the rack frame. This can help to further minimize voltage differences and improve the overall grounding system.

How it's Usually Achieved (Practical Steps)


Identify the Main Panel Grounding Bus

Locate the grounding busbar in the electrical panel that supplies power to the rack.2.

Dedicated Grounding Conductor (Recommended)

Run a dedicated grounding conductor (typically green insulated wire) from the rack to the main panel grounding busbar. The size of this conductor should be based on the size of the branch circuit serving the rack, according to NEC Table 250.122.
3.

Bonding to Rack Frame

Connect the grounding conductor to a grounding lug or terminal block on the rack frame. Ensure that the connection is clean, tight, and free of corrosion.4.

Power Strip/PDU Grounding

Ensure that each power strip or PDU is properly grounded through its power cord and its mounting to the rack. If necessary, add supplemental bonding conductors between the power strip/PDU enclosure and the rack frame.5.

Equipment Grounding

Verify that all equipment connected to the rack has a proper grounding conductor in its power cord. If not, replace the power cord with one that does.6.

Supplemental Bonding (Optional)

Run supplemental bonding conductors between the chassis of key equipment and the rack frame.7.

Verify Continuity

Use a multimeter to verify the continuity of the grounding system. Ensure that there is a low-impedance path between all parts of the rack, the power strips/PDUs, the equipment chassis, and the main panel grounding bus.8.

Documentation

Document the grounding system, including the size and routing of grounding conductors, the location of grounding connections, and the results of continuity tests.

Important Considerations



Clean Connections

Ensure all connections are clean, tight, and free from corrosion. Use anti-oxidant compound on aluminum connections.

Proper Sizing

Properly size the grounding conductors according to the NEC tables.

Conduit vs. Flexible Metal Conduit

Use rigid metal conduit or electrical metallic tubing (EMT) where possible. If flexible metal conduit (FMC) is used, ensure that it is listed for grounding purposes and that it is properly connected. Liquidtight Flexible Metal Conduit (LFMC) is okay, but often requires a separate grounding conductor to be run inside the conduit.

Overlapping Requirements

There may be requirements from other standards or regulations, such as local building codes or industry-specific guidelines. Always consult with a qualified electrical engineer or electrician to ensure that the grounding system meets all applicable requirements.

Changes and Modifications

Any changes or modifications to the grounding system must be performed by a qualified electrician and must comply with all applicable codes and regulations.

Don't rely solely on paint for connectivity

Remove paint under grounding lugs for a good metal-to-metal connection.

Grounding Busbars

Consider using grounding busbars within the rack to provide a convenient point for connecting multiple grounding conductors.

Consider an IT Grounding Audit. Many electrical contractors perform a full IT grounding audit to identify and resolve issues.

Example Scenario

Imagine a server rack with a PDU supplying power to multiple servers.1.

GEC/EGC Connection

A #6 AWG green wire is run from the rack frame to the building's electrical panel grounding bus. This acts as the primary grounding conductor for the rack.2.

PDU Grounding

The PDU is plugged into a standard 20A receptacle. Its power cord contains a green grounding wire that connects the PDU's metal enclosure to the receptacle's grounding terminal.3.

Server Grounding

Each server is plugged into the PDU. The server's power cord contains a green grounding wire that connects the server's chassis to the PDU's grounding terminal.4.

Supplemental Bonding

To further improve grounding, a short length of #10 AWG green wire is run between each server's chassis and the rack frame.5.

Rack door is connected to rack frame via a bonding strap.Safety First!

Working with electrical systems can be dangerous. If you are not qualified to work with electricity, hire a licensed electrician to perform the work. Always de-energize the circuit before working on any electrical equipment.Disclaimer: This information is for educational purposes only and should not be considered a substitute for professional electrical advice. Always consult with a qualified electrical engineer or electrician to ensure that your grounding system meets all applicable codes and regulations. Flag for review