Let's break down this scenario and the relevant NEC (National Electrical Code) requirements to determine the correct answer.

Understanding the Key Concepts EGC (Equipment Grounding Conductor)

The EGC provides a low-impedance fault current path back to the source (transformer) to facilitate the operation of the overcurrent protective device (OCPD, like a circuit breaker) in case of a ground fault. This is critical for safety, preventing dangerous voltage from appearing on equipment enclosures and minimizing shock hazards.

Fault Current

The current that flows during a ground fault. The EGC's purpose is to provide a path for this current back to the source.

NEC 250.134

This section requires that exposed noncurrent-carrying metal parts of fixed equipment, if likely to become energized, must be connected to an equipment grounding conductor.

NEC 250.118

This Section lists acceptable types of EGCs.

NEC 250.122

This Section specifies the minimum size of the EGC based on the rating of the overcurrent protective device.

NEC 300.3(B)

This Section states that all conductors of the same circuit, including the EGC, must be run together in the same raceway.

Flexible Metal Conduit (FMC)

Flexible metal conduit is an approved wiring method and may be used as an EGC if installed in a way that meets certain requirements. (250.118(5)).

Analysis of the Scenario1. The Need for EGCs

The equipment, including the heater flanges and the heavy steel piece, is likely to become energized in a fault condition. Therefore, an EGC is absolutely required for each heating circuit to ensure proper safety.2.

Sizing the EGC

Each heating circuit has a 50A OCPD. Referring to NEC 250.122, a 10 AWG copper EGC is the minimum size required for a 50A OCPD.3.

EGC Placement

NEC 300.3(B) is very important. It states that all conductors of the same circuit, including the EGC, must be run together in the same raceway. This is to minimize impedance and ensure effective fault current flow.4.

FMC as EGC

NEC 250.118(5) and 250.102 provide requirements for using flexible metal conduit as an EGC. When used as an EGC, it must be installed in a manner that ensures electrical continuity and has low enough impedance to handle the likely ground fault current.

Evaluating the Options a. run a seperate 10AWG copper EGC in each of the conduit? This is the MOST correct answer. It ensures each circuit has its own dedicated ground, meeting the sizing requirements and placement rules. This is the safest and most compliant approach. If the FMC is not approved as an EGC this is the only possible solution. b. run a single 10AWG copper EGC in one of the 10 conduits? This is incorrect. It does not provide a proper fault current path for the other nine circuits. It violates NEC 300.3(B) (all conductors of the same circuit must be in the same raceway). Also this is undersized based on the total possible fault current. c. run a single 10AWG copper EGC by itself in its own conduit? This is also incorrect. It violates NEC 300.3(B). The EGC must be run in the same raceway as the circuit conductors it serves. Additionally, a single 10 AWG EGC would be woefully undersized for the combined potential fault current of all ten 50A circuits.

Conclusion

The correct answer is a. run a seperate 10AWG copper EGC in each of the conduit?Important Considerations



Local Codes

Always verify and adhere to any local electrical codes or amendments to the NEC that may be in effect in your jurisdiction.

Engineering Judgement

Complex installations may benefit from an engineering review to ensure optimal safety and code compliance. Factors such as total fault current contribution, impedance, and bonding practices could influence the specific design.

AHJ Approval

When in doubt, consult with your local Authority Having Jurisdiction (AHJ) for clarification and approval of your grounding plan.

FMC Approval: Verify that the FMC is approved as an EGC and installed per the manufacturer's and code requirements. Using a separate EGC is generally the best practice as it provides a dedicated path and does not rely on the integrity of the conduit couplings. Flag for review