Under what condition is the equipment grounding conductor allowed to be run separately from the circuit conductors?

The condition that allows the equipment grounding conductor to be run separately from the circuit conductors is when a nongrounded-type receptacle is replaced. This is specifically relevant in situations where the electrical system does not have an existing equipment grounding conductor that can be used.

When replacing a nongrounded-type receptacle, it is often necessary to provide a proper equipment ground. Running a separate equipment grounding conductor ensures safety and compliance with the National Electrical Code (NEC). In these cases, the separate grounding conductor can be installed from the receptacle back to the panel or another suitable ground source, facilitating a safe and effective grounding system.

Additionally, this approach assists in reducing potential shock hazards and improves overall electrical safety, which is particularly critical when dealing with equipment that may not have been grounded originally. It reflects a best practice in electrical installations to ensure that all components are adequately grounded, especially when upgrades or replacements are made.