ECM Buyers' Guide
  

Code Quiz

What is/are the appropriate electrode(s) required to ground a 112.5kVA transformer installed as a separately derived system? The transformer is located 500 feet from the service equipment in a separate electrical room. Metallic water piping runs throughout the structure. The framework of the building is structural steel, and there's neither a ground ring nor access to rebar installed in the footings. The building electrical system is grounded in accordance with all the applicable rules of Art. 250 of the 2005 NEC.

A) A grounding electrode conductor connection to the metal water piping system in the area of the separately derived system only.
B) A grounding electrode conductor connection to the structural steel in the area of the separately derived system only.
C) Either one of the electrodes in A or B by itself is acceptable.
D) Either one of the electrodes in A or B is acceptable as the grounding electrode only if the other electrode is also connected (bonded) to the same point of the separately derived system where the grounding electrode conductor connection of the system is also made.

Answer: D)

Explanation: Sec. 250.30(A)(7) Grounding Electrode intends that the grounding electrode shall be as near as practicable to and preferably in the same area as the grounding electrode conductor connection to the system. It’s clear that the nearest electrode to the separately derived system shall be used. There’s no rule that doesn’t permit the use of both electrodes (metal water piping system or structural metal), but the use of only one of the electrodes is acceptable.

Per a 2005 NEC change, 250.104(D)(1) requires that both the structural steel and the metallic water piping in the area of the separately derived system (if both are in the area of the separately derived system) be bonded to the same point on the separately derived system where the grounding electrode conductor connection to the system is made.

In-other-words, use the electrode of your choice (closest to the separately derived system), but don't forget to bond the metal grounding electrode, and the metal water pipe electrode in the area of the separately system to your separately derived system at the same point as the connection of the grounding electrode conductor.

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 necexpert@aol.com.


Want to use this article? Click here for options!





Acceptable Use Policy
blog comments powered by Disqus

what's wrong here?

What's Wrong Here?

Feb 2, 2012 7:54 PM

What's Wrong Here?

Jan 19, 2012 4:06 PM

What's Wrong Here?

Jan 5, 2012 11:53 AM

View all What's Wrong Here?

product spotlight

Emergency lighting controls

Feb 9, 2012 8:40 AM

Emergency lighting controls

The UL924 emergency lighting control relay (ERC) mounts in the ceiling and features an automatic diagnostic feature ...

View all 2012 Product Spotlights

Free Product Info

Our Product Information site is the ultimate online resource for products and services offered by Advertisers featured in our Magazine. This service is provided as a quick and easy way to request Product Information online. Get FREE product information now.

Recent Comments

More...


Social Media

More ways to stay informed...

follow us on twitter

Find us on Facebook

EC&M TV

Arlington CP9000

Arlington's new 9" diameter ceiling cover plate is the neatest way to cover unused "high hat" cans. With no tools needed, installation couldn't be faster!...

Arlington Gangable Boxes

Designed for new or retrofit applications, these snap-together gangable plastic boxes eliminate the need to construct a multiple-gang steel box out of several individual ones...

Understanding NEC Requirements for Solar Photovoltaic Systems
During this session, Mike Holt will address possible conflicts or confusing NEC requirements, provide tips on proper electrical installation techniques, and discuss the dangers related to improper installations. View this On Demand Webinar!



resources

product info icon

product info

tradeshow icon

tradeshow

research icon

research

industry links

industry links

rss icon

rss

Browse Back Issues

Browse Back Issues