Code Quiz

Aug. 26, 2010
With respect to interconnected electric power production sources (Art. 705), is it required to automatically disconnect a 3-phase primary power source from all ungrounded conductors when one of the phases opens to create a loss of power on one or more phases?

With respect to interconnected electric power production sources (Art. 705), is it required to automatically disconnect a 3-phase primary power source from all ungrounded conductors when one of the phases opens to create a loss of power on one or more phases? For this example, exclude emergency or legally required standby systems — and exclude the exception for this rule.

  1. Yes, as per Sec. 705.42.
  2. No. This applies to single-phase systems only.
  3. No. This applies to 2-phase, 5-wire systems only.
  4. No. There is no such requirement in the 2008 NEC. This is considered a "best practice" suggestion.

Answer: A

Excluding emergency or legally required standby systems — and the exception noted in 705.42 — you are required to design and install the system to automatically disconnect a 3-phase primary power source from all ungrounded conductors when one of the phases of that 3-phase primary source opens to create a loss of power on one or more phases.

Owen is the owner and president of National Code Seminars and the holder of master electrician certifications in 46 states. He can be reached at [email protected].

About the Author

Steven Owen

Voice your opinion!

To join the conversation, and become an exclusive member of EC&M, create an account today!

Sponsored Recommendations

Electrical Conduit Comparison Chart

CHAMPION FIBERGLASS electrical conduit is a lightweight, durable option that provides lasting savings when compared to other materials. Compare electrical conduit types including...

Fiberglass Electrical Conduit Chemical Resistance Chart

This information is provided solely as a guide since it is impossible to anticipate all individual site conditions. For specific applications which are not covered in this guide...

Considerations for Direct Burial Conduit

Installation type plays a key role in the type of conduit selected for electrical systems in industrial construction projects. Above ground, below ground, direct buried, encased...

How to Calculate Labor Costs

Most important to accurately estimating labor costs is knowing the approximate hours required for project completion. Learn how to calculate electrical labor cost.