How Far Do Electrodes Extend?

Mar 1, 1998 12:00 PM, Frederic P. Hartwell

Do grounding electrodes end at the building wall, or do they continue on into the building? How does that affect the application of other Code rules?

Code rules cover attaching a grounding electrode conductor to a grounding electrode, and also restrict the use of splices in grounding electrode conductors. To apply these rules consistently, you need to know where the electrode ends and where a grounding electrode conductor begins.

For example, what happens when a concrete-encased electrode in the form of a No. 4 or larger conductor extends out of the concrete without joint, or you have a ground ring conductor long enough to extend well into a building? What about a water pipe extending far into the building? How about building steel at great heights within a high-rise building?

The EC&M Panel's response In general, and absent any Code rule to the contrary, we think the term "grounding electrode" (undefined in the Code) is the object in contact with the earth as prescribed by the Code, whatever its size and however far it extends into the building. In other words, the electrode continues until there is a physical discontinuity. You have to look at this electrode by electrode, however.

Building steel. This is the easiest case, so we'll start here. We think effectively grounded building steel is an electrode however far it extends into the building, even to the top of a high-rise building. The key here is the express language in Sec. 250-81(b) describing this electrode as the "metal frame of the building;" obviously this is something that extends all the way up.

Water piping. We think that, in principle, this electrode also extends into the building an undefined distance. Sec. 250-112 provides in part:

Where necessary to ensure [a permanent and effective ground] for a metal piping system used as a grounding electrode, effective bonding shall be provided around insulated joints and sections and around any equipment that is likely to be disconnected for repairs or replacement.

This would make no sense if the interior water piping system weren't eligible for consideration as a grounding electrode. However, due to documented instances where other trades have interfered with the continuity of the piping system, the Code does limit the usability of this electrode within buildings in Sec. 250-81. You can't use this piping system for that purpose beyond 5 ft of the building entrance, unless you're in a industrial or commercial building with qualified maintenance and supervision, and unless the entire length of the piping system you'll be relying on to maintain grounding continuity is exposed.

This last condition may require some field interpretation, since piping systems are rarely exposed over their entire length. For example, a pipe passing through fire-stopping in a partition isn't literally exposed at that point. Most inspectors will allow this, but be sure. Fortunately, location above a suspended ceiling isn't a problem; the wording of the exception was changed in the adoption process from "visible" to "exposed." Per Art. 100, that includes a location behind removable panels.

Concrete-encased electrodes and ground rings If these are conductors and go all the way to the service equipment, do they become grounding electrode conductors at any point? Suppose you cut one short, and need to extend it to a panel; can you use a conventional split-bolt connector for this?

We think that where the conductor emerges from the wall, it's still part of the electrode, just as the other electrodes in Sec. 250-81 enter buildings. We think the Code allows for one conventional mechanical connection, just as for connections to other electrodes , even (in this case) at some distance from the building entrance. If you need more than that (thereby increasing the risk), use the better connections (the irreversible compression or exothermic welding provisions covered in Sec. 250-92(a) Ex. 3) for the additional splices. Naturally, this doesn't prevent you from either avoiding joints at all (the best idea) or using the better connections throughout.

Want to use this article? Click here for options!

Acceptable Use Policy

blog comments powered by Disqus

in this issue

product spotlight

EV charger tester

May 25, 2012 8:26 AM

The Electrician is portable tester that verifies critical power and safety requirements of electric vehicle (EV) chargers...

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.