We Wrote The Book on Grounding and Earthing

Toll Free: 888.367.0888

Ask The Experts Blog

By U.S. code, can I insert a device in the path of the Protective Earth Ground Conductor?

Peter asks us:

By U.S. code, can I insert a device in the Protective Earth Ground conductor at the panel of a lighting branch that has:

1. A  fault current AC voltage drop of less than 2 volts.

2. A peak current capability of 150 amps 3. Effectively has no inductance or capacitance for fault currents.

Hi Peter,

Thank you for your excellent question regarding the Grounding Electrode Conductor.  It is our pleasure to assist you.

First of all, when you say “Protective Earth Ground Conductor” we are assuming you mean the “Grounding Electrode Conductor (GEC)”.  In common terms, the Grounding Electrode Conductor (GEC) is the wire that runs from the ground-bar in the electrical cabinet to the top of the ground rod.  The goal of this conductor is to provide a low-impedance electrically conductive path designed to carry the anticipated ground-fault currents to the earth connection (electrode). Please let us know if this is not what you meant. 

Article 250.64 of the National Electrical Code (NFPA 70) governs the installation of the Grounding Electrode Conductor (GEC).  This particular article is quite extensive, covering two (2) full pages of text.  The primary concerns of the article are with:

1. Proper conductor type (copper or aluminum) and size (#8 to 3/0) so as to be able to handle anticipated faults

2. Protection from physical damage (conduit and routing)

3. That the conductor (GEC) is one continuous piece (no breaks)

4. That the conductor (GEC) is properly bonded to electrodes, building steel, water pipe, conduit, etc.

Article 250.66 and Table 250.66 deal with proper sizing of the Grounding Electrode Conductor (GEC) which is based on the size of the largest incoming power line.

It sounds from your email, that you are wanting to insert a new device in series with the Grounding Electrode Conductor, and that this insertion would ‘break’ the continuous conductor rule.  The National Electrical Code (NEC) does allow splicing of the Grounding Electrode Conductor (Article 250.64 (C)(1)) as long as the splice is made using irreversible compression-type connectors or exothermic welds.

You mention that the device will have a peak current capability of 150-amps.  This is a concern in that the Grounding Electrode Conductor (GEC) must be large enough to handle the short-circuit fault for the panel, for the length of the fault clearing time, and for the X/R ratio of the fault.  Even in your typical home electrical panel rated for only 100 amps, the short-circuit fault current can be 10,000 RMS symmetrical amps or more.  For a typical 3-phase 600 amp electrical panel you may find for a business, the fault current can easily exceed 60,000 RMS symmetrical amps!  If your device is in series with the Grounding Electrode Conductor, it will need to be able to handle the short-circuit current rating of the panel it is installed in.

In regards to the 2-volt drop, we are assuming this is measured using a volt-meter in parallel, across the device from GEC to GEC.  Was this using a 150-amp current level?  If so, this would mean that the device has a 0.013-ohm resistance.  Is this correct?  If so, a 10,000-amp short circuit fault would develop a 130-volt drop.

Now to the root of your question; is it legal to install such a device under US code?  Assuming that your device will be placed in series with the Grounding Electrode Conductor, that it is capable of handling the short-circuit current rating, has irreversible connections, and provides a low-impedance path… You still have an uphill battle.  The bottom line is that the National Electrical Code (NEC) is quite clear, you may not impede the Grounding Electrode Conductor (GEC) connection in anyway.  However, that does not mean it is impossible to get such a device approved.

You would first need to start by gathering as much scientific evidence on your own as is possible.  Then you would approach the Underwriters Laboratory (UL) and work with them on a “UL Fact Finding Report”.  It will be important to have your own data before you start this process, lest they lead you down a very expensive path.  You would also need to get a special “UL Listing” for your device.  Once these are done, you would be free to approach the Plan Checking Departments of individual city’s within the United States and install your product with their approval.  Meanwhile the UL (and your lawyers) would help you get the National Electrical Code amended to allow the use of any product certified under the new UL Listing.  This will take years, and a lot of money.  However, it can be done.

We have some experience in this area, and are of course happy to help you with this process.  If you should have any questions, please do not hesitate to call one of our Engineers  and we will be glad to discuss your issues with you free of charge.

Best regards,

The Engineering Team at E&S Grounding Solutions

Photo credit: http://www.flickr.com/photos/ddfic/456841106/sizes/o/in/photostream/

Leave a Reply