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Just a quick note to thank you for the fine work you and your staff are doing in providing accurate technical information to field personnel. I am a Senior Service Technician with the Department of Transportation, and part of my duties pertains to illumination of our interchange locations across our state.
After reviewing our lighting standards and current installation practices, it was apparent that these standards did not conform to NEC, and they needed to be changed. The problem was that we only provided two conductors out to our 480V tower lights. We did not provide a low impedance path with the capacity to safely carry the maximum ground-fault current likely to be imposed on it [110.10]. But we did drive ground rods next to each of the metal light poles.
Needless to say, this system would not
clear a ground-fault and not open the circuit overcurrent protective device. These were
changes that needed made not just for code compliance, but the real life issues of maintaining
a safe 480V system in a wet location.
Mike's Comment: I'm pleased to see that my effort regarding the difference between bonding and grounding is actually making a difference, and maybe it will save a life or two. There are way too many unnecessary deaths caused by people contacting energized metal parts that have been grounded to a ground rod, but not bonded to an effective ground-fault path [250.2 and 250.4(A)(5)].
Much of this confusion between grounding and bonding lies with the NEC's definition and use of the term 'ground,' when in fact the application is bonding to an effective ground-fault current path [250.2(A)(3)]. For example, the NEC in 250.86 requires all metal raceways and enclosures to be grounded. Naturally the NEC does not want us to ground the metal parts to the earth to clear a fault.
Note: The NEC's definition of ground is "the connection to the earth, or some body that serves the place of earth" (I wonder what that means).
2008 NEC: A task group appointed by the NEC correlating committee is reviewing the NEC's use of the term ground and grounding, when the intent is bond or bonding to an effective ground-fault current path. I pray that this committee will propose some changes for the 2008 NEC to clarify the required practice.
However, many industry 'old timers'
are against changing of the term grounding to bonding. They say, "it's been that
way for over 100 years, not need to change now. "My thoughts? Just because it's been
wrong for over 100 years, there is no need to subject the next generation of electrical
professionals to this confusion.
Example: A 25 ohm resistance ground rod will only carry 4.8A at a 120V ground fault (I = 120V/25 ohms).
For the past 12 years I have been preaching that we must bond metal parts to an effective ground-fault current path [250.2] in accordance with 250.4(A)(3), not ground them to the earth to clear a fault.
Note: The above comments are in reference to 120V, 120/208V, 120/240V, 277/480V, and 347/600V solidly-grounded systems.
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