GROUNDING IN THE 1987 CODE

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TOMMY BASHLOR

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I AM REQUESTING AN INTERPRETATION OF THE 1987 CODE SECTION 250-81,250-83 AND 250-84
CAN THE 250-84 REQUIREMENT "WHEN A SINGLE ELECTRODE CONSISTING OF A ROD , PIPE,OR PLATE WHICH DOES NOT HAVE A RESISTANCE TO GROUND OF 25 OHMS OR LESS SHALL BE AUGMENTED BY ONE ADDITIONAL ELECTRODE"BE MET BY THE ADDITION OF A COLD WATER PIPE MORE THAN TEN FEET AWAY AND MORE THAN TEN FEET IN LENGTH BURIED IN THE EARTH?
FOR YOUR INFORMATION
THE RESISTANCE OF THE ROD IS 280 OHMS,THE COLD WATER PIPE HAS A RESISTANCE OF 192 OHMS,THE ENTIRE SYSTEM HAS A RESISTANCE OF 2.8 OHMS. DOES IT EVEN MATTER WHAT THE RESISTANCE IS AS LONG AS YOU HAVE THE GROUND ROD SUPPLEMENTED BY THE COLD WATER PIPE?
 
Re: GROUNDING IN THE 1987 CODE

Tommy, welcome to the forum. Please avoid using Caps Lock, we see it as shouting. :)

The ground rod is supplementing the water pipe, so the water pipe cannot be the second electrode installed to supplement the ground rod. :D

If the ground rod has over 25 ohms, you need another one. ;)
 
Re: GROUNDING IN THE 1987 CODE

Ditto.

If we ever get a "frequently asked questions forum", I think the second ground rod question qualifies ;)

Steve
 
Re: GROUNDING IN THE 1987 CODE

This was inadvertently posted as a ?New Thread.? I have moved it here, so as to permit the discussions to continue.
Originally posted by TOMMY BASHLOR:
George and Steve,
So your telling me that if i had a commercial service that i installed and it had a continous grounding electrode conductor from the main disconnecting means to a ground rod and then to cold water pipe,meeting the ten foot in length rule,buried in the earth and there are no other grounds avaiable that it would be a code violation.?

Does it matter if i have a resistance of 25 ohms or less as long as i have two electrodes?
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Re: GROUNDING IN THE 1987 CODE

What you describe may or may not be a code violation. In order to tell, we would have to know the ground resistance of the rod (not the pipe). And let us be clear: The resistance of the metal (in the rod or in the pipe) is not what we need to measure. Rather, we measure the resistance between two points: (1) The point at which the grounding electrode conductor (GEC) is attached to the grounding electrode, and (2) Planet Earth.

Using the water pipe as a grounding electrode is a separate requirement from the 25 ohm thing. If all you have is the water pipe, then you have to install a supplemental electrode. If you chose to use a ground rod as the supplemental electrode, then it has to have a resistance to ground of 25 ohms or less. Most electrical contractors do not have the equipment or the time necessary to make the applicable measurements. Instead, they take advantage of 250.56 (2002 version), which says that if you install a second rod (this is to augment the first rod, and is not related to the water pipe), then you can quit there. You don?t have to measure anything.

[ April 15, 2005, 01:07 PM: Message edited by: charlie b ]
 
Re: GROUNDING IN THE 1987 CODE

1987 NEC Chapter 250 H. Grounding Electrode System

250-84. Resistance of Made Electrodes. A single electrode consisting of a rod, pipe, or plate which does not have a resistance to ground of 25 ohms or less shall be augmented by one additional electrode (my emphasis - Al) of any of the types specified in Section 250-81 or 250-83. Where multiple rode, pipe, or plate electrodes are installed to meet the requirements of this section, they shall be not less than 6 feet (1.83 m) apart.

(FPN): The paralleling efficiency of rods longer than 8 feet (2.44 m) is improved by spacing greater than 6 feet (1.83 m).
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It occurs to me to wonder, since your original question describes this as a "commercial" installation. . .were there specifications from an engineer or architect that were part of the original plans?
 
Re: GROUNDING IN THE 1987 CODE

I take it that this service was built back when 1987 rules were in effect, am I correct?

One problem with some water services is that some water companies deliberately insert a dielectric coupling between the water service pipe and the water main. This keeps the water main from acting as a ground bus so that water main workers are less likely to be shocked if there is an electrical service with an open neutral.
 
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