You can use metallic conduit (rigid metal conduit - RMC, intermediate metal conduit - IMC, and electrical metallic tubing - EMT) as a grounding conductor. In fact, it's one of the primary methods for grounding electrical systems.

The common misconception arises because:1. It's not the only acceptable method, and it must be installed correctly.2. It's not always the best method in all situations, and there are specific rules about using it as a grounding conductor.3. There are situations where relying solely on the conduit as a grounding conductor is problematic and may require supplemental grounding.4. The type of fitting used matters greatly.

Here's a breakdown

Why Metallic Conduit CAN be Used as a Grounding Conductor:
Continuity

When properly installed with listed fittings, metallic conduit creates a continuous, low-impedance path back to the source (service equipment). This path is essential for effectively clearing ground faults. This low impedance allows a sufficiently high fault current to flow, tripping the overcurrent protective device (breaker or fuse) quickly, thus preventing dangerous voltage on metal enclosures.

NEC Recognition

The National Electrical Code (NEC) specifically recognizes RMC, IMC, and EMT as acceptable equipment grounding conductors. See NEC Article 250, particularly 250.118.

Protection

Metallic conduit also provides physical protection for the wiring contained within.

Conditions & Requirements for Using Metallic Conduit as Grounding



Listed Fittings



This is absolutely critical. The fittings used to connect conduit sections and connect the conduit to enclosures must be listed for grounding. This means they have been tested and approved to maintain electrical continuity under fault conditions. Using non-listed fittings can create high impedance connections, negating the grounding capability of the conduit. This is a frequent violation. Tightening

Fittings must be properly tightened to ensure a good electrical connection. Loose fittings create resistance.

Material Compatibility

Consider galvanic corrosion between dissimilar metals. Use compatible fittings and consider using anti-oxidation compound.

Adequate Size

The conduit itself must be sized appropriately for the circuit's overcurrent protection. While it's often adequate, you can't assume a small EMT is sufficient for a very large service. NEC 250.122 provides guidelines for the minimum size of equipment grounding conductors.

Integrity

The conduit must be structurally sound and free from damage. Severe corrosion or damage can compromise its ability to conduct fault current.

Concentric Knockouts

Care should be taken when breaking out concentric knockouts. Sharp edges can damage the grounding contact area and reduce effective grounding. Using grounding bushings can help ensure a good connection.

Isolation

While the conduit is the grounding conductor, equipment that is double insulated, for example, may not use the metallic conduit for grounding. Follow manufacturers installation instructions to avoid any missteps in this area.

Situations Where Supplemental Grounding May Be Required or Preferred



Long Runs

For very long conduit runs, the impedance of the conduit itself can become significant, potentially slowing down fault clearing. Adding a supplemental equipment grounding conductor (EGC) inside the conduit can help reduce impedance.

Critical Equipment

For sensitive electronic equipment, a dedicated low-impedance grounding path is often preferred. A supplemental EGC can provide this.

Noisy Environments

In areas with high electrical noise, a dedicated EGC can help reduce noise on the grounding system.

Specific Equipment Requirements

Some equipment manufacturers may require a dedicated EGC in addition to the conduit for grounding.

Isolated Ground Receptacles

For isolated ground (IG) receptacles, a separate insulated grounding conductor must be run back to the service equipment. The conduit cannot be used as the sole grounding conductor for IG receptacles.

Why the Confusion? (Recap)



Misinterpretation of Code

The NEC doesn't prohibit using metallic conduit as a grounding conductor, but it does specify the conditions under which it's acceptable.

Importance of Listed Fittings

The biggest problem is the use of incorrect or poorly installed fittings. These create high-resistance connections, defeating the purpose of the grounding system.

Misunderstanding the Role of Supplemental Grounding

Supplemental grounding doesn't mean the conduit can't be used for grounding; it means that in certain circumstances, it's beneficial to add an additional grounding conductor.

Emphasis on Safety

Electrical codes are constantly evolving to improve safety. While conduit is generally a good grounding conductor, it's essential to understand the limitations and take precautions to ensure a safe installation.

In Summary

Metallic conduit (RMC, IMC, and EMT), when properly installed with listed fittings*, is a code-recognized and effective equipment grounding conductor. However, always consider the length of the run, the sensitivity of the equipment being served, and the potential for noise or other issues that might warrant a supplemental equipment grounding conductor.

Always consult the NEC and local electrical codes for specific requirements in your area. When in doubt, consult with a qualified electrician. Flag for review