You're right to question that! In most cases, you do not need a separate EGC (Equipment Grounding Conductor) for each circuit when running multiple circuits in the same conduit.Here's the breakdown of why and when you can use a single EGC: The Primary Principle

The purpose of the EGC is to provide a low-impedance path back to the source (the panel) in the event of a ground fault. This allows a high fault current to flow, tripping the overcurrent protective device (circuit breaker or fuse) quickly and safely.

Shared Fault Current Path

If multiple circuits are in the same conduit, a fault on any one circuit will utilize the EGC as the return path. The conduit itself, if properly connected, can also contribute to the fault current path.

NEC Requirements (General Rule)

The NEC (National Electrical Code) generally allows a single EGC to serve multiple circuits within the same raceway (conduit, etc.) if the following conditions are met:

Sized Correctly

The EGC must be sized according to the largest overcurrent protective device protecting any of the circuits within the raceway, as per NEC Table 250.122. You look at the rating of the largest breaker in the conduit, and size the EGC accordingly.

Proper Connections

All connections to the EGC must be made so as to ensure a low-impedance connection.

All Circuits from the Same Source

All circuits in the conduit must originate from the same electrical panel or separately derived system.

Exceptions (When Separate EGCs Might Be Required)



Isolated Ground Receptacles (IG)

If you have circuits feeding isolated ground (IG) receptacles, those circuits do require their own dedicated EGC that is run all the way back to the source without contacting the conduit or any other EGC along the way. These are used in sensitive electronic equipment applications to minimize noise.

Some Types of Flexible Metal Conduit (FMC) and Liquidtight Flexible Metal Conduit (LFMC)

Depending on the length and the overcurrent protection of the circuits, these types of flexible conduit may require a supplemental EGC to be run within them. NEC 250.118 outlines the requirements for using FMC and LFMC as an EGC.

Specific Equipment Instructions

Some equipment instructions may require a dedicated EGC, regardless of other factors. Always follow the manufacturer's instructions.

Derating

While not requiring separate EGC's, a contractor may choose to run a seperate EGC for each circuit when there is a large number of current carrying conductors as the EGC is also considered a current carrying conductor and could require derating of the conductors in the conduit.

In summary

For typical multi-wire branch circuits (MWBCs) or multiple standard circuits in a single conduit, you usually only need one EGC, sized appropriately for the largest breaker. However, always double-check for the exceptions, especially concerning isolated grounds and flexible metal conduit. And, of course, always* consult the NEC and local electrical codes for the final word and guidance.

Important Disclaimer: I am an AI chatbot and cannot provide electrical advice. Electrical work can be dangerous, and mistakes can lead to fire or electrocution. Always consult with a qualified and licensed electrician for any electrical work. They can properly assess your specific situation and ensure that all work is done safely and according to code. Flag for review