yesterlectric
Senior Member
- Location
- PA
- Occupation
- Electrician
Reviewing article 547. So far, the only farm premises I have worked on have been smaller applications. I worked on one premises with an outdoor equipment rack that housed the main service disconnect and had feeders going to barn, house, other outbuilding. I've seen one installation where there were two separate services. I don't have specific experience with seeing an outdoor, site isolation device that is not considered service equipment, but reading the article, I wonder if it would require some revision.
First, 547.1 says the entire article shall apply to buildings or that portion of buildings that are similar in nature to those described in 547.1 A&B. Then, it goes on to describe that a distribution point like described in 547.9 is allowed. Many installations may have only a few of the several buildings with the hazards described in 547.1 A&B, but this is describing something more general to agricultural buildings regardless of dust/corrosion risks.
Perhaps the scope of the article should change, the there should be a part II added to cover specific wiring methods and protections for those portions of a agricultural premises exposed to dust/corrosion hazards.
Second thing that trips me up a little is 547.9(B)(3)-1. It requires the equipment grounding conductor between the site isolation device and the service disconnecting mean(s) be not smaller than the largest supply conductor. I would think that the reason for this requirement is that this conductor is being relied upon to handle fault current that would run all the way back to the site isolating device before completing the circuit through the neutral, and there is concern about it being undersized and not being able to enable the over-current device to operate upon a fault condition. The issue is that it says if the EGC is of different material, then it shall be sized per the equivalent size of table 250.122. If the goal is to ensure the ampacity (or resistance) of the EGC is at least as good at the ungrounded conductors, then it would seem that it should either just require it to have the same ampacity, or that it should reference the equivalent size table of that of article 310.
Does anyone agree on this?
Here's one reference:
http://www.adamselectric.coop/wp-content/uploads/2015/02/Agricultural-Buildings.pdf
First, 547.1 says the entire article shall apply to buildings or that portion of buildings that are similar in nature to those described in 547.1 A&B. Then, it goes on to describe that a distribution point like described in 547.9 is allowed. Many installations may have only a few of the several buildings with the hazards described in 547.1 A&B, but this is describing something more general to agricultural buildings regardless of dust/corrosion risks.
Perhaps the scope of the article should change, the there should be a part II added to cover specific wiring methods and protections for those portions of a agricultural premises exposed to dust/corrosion hazards.
Second thing that trips me up a little is 547.9(B)(3)-1. It requires the equipment grounding conductor between the site isolation device and the service disconnecting mean(s) be not smaller than the largest supply conductor. I would think that the reason for this requirement is that this conductor is being relied upon to handle fault current that would run all the way back to the site isolating device before completing the circuit through the neutral, and there is concern about it being undersized and not being able to enable the over-current device to operate upon a fault condition. The issue is that it says if the EGC is of different material, then it shall be sized per the equivalent size of table 250.122. If the goal is to ensure the ampacity (or resistance) of the EGC is at least as good at the ungrounded conductors, then it would seem that it should either just require it to have the same ampacity, or that it should reference the equivalent size table of that of article 310.
Does anyone agree on this?
Here's one reference:
http://www.adamselectric.coop/wp-content/uploads/2015/02/Agricultural-Buildings.pdf