250.4 clearly states that electrical systems that are grounded shall be connected to earth in a manner that will limit the voltage imposed by lightning... It then goes on to talk about grounding and bonding of electrical equipment and other conductive materials that are "likely to become energized". At what point are the grounding and bonding requirements required to deal with lightning protection and not just ground faults within the electrical system?? For example, would a metal chimney extending up above the highest point of the structure require bonding?? Why or why not?? If so, how do you determine the size of the bonding conductor? Let's say the metal fireplace has a fan. #14 AWG circuit with equipment ground. Is that sufficient to withstand a lightning strike? Just curious how others view the wording of 250.
Don, I am well aware of 780, nevertheless, those words ARE in the NEC, have been for YEARS. What do they really mean? Do they apply only to lightning voltages coming from the utility or source of supply?
Re: "...likely to become energized..."#8139608/07/0210:37 PM
In my opinion, the NEC in 250.4(A)(1) is talking about limiting the voltages on the electrical system that result from outside influences such as lightning. Note that it does use the word system in this section. The other parts of this section use the word "equipment" and for the most part also uses the words "fault clearing path". I don't see anything that requires lightning protection of the electrical equipment or other conductive equipment in the NEC. Don