Arc-fault breaker use in in subpanels.
Joe Sullivan
| Posted in Energy, Heating & Insulation on
I am about to run electrical service to a subpanel in a farm building from a larger subpanel in another farm building. Everything is very well grounded at both panels (4 8′ rods each with #4 wire and cadwelds). The question is, it I use one of the new arc-fault breakers at the first subpanel, will it be effective for all the branch circuits at the second panel, or do I need to use them IN the second panel to be effective.
Before anyone points this out, yes,I am not a licensed electrician, and yes, I do know that electricity is tricky and risky. That is why I am asking…
J
Replies
I'm curious on why you would even want arc faults in a barn.
The dang things on my job site trip with almost every tool I have & forget about runnin the smallest of plasma cutters.
Interesting. I didn't know they did that.The reason I am considering them is that it is a cedar horse barn with an oak and pine frame and arcs and flames scare me. Arc fault breakers seemed like a good idea. I am all ears for problems with them, though.J
Joe,
I understand you are not an electrician but you should read NEC Article 547 particularly since you are feeding this panel from another farm building.
There is some controversy regarding the equipotential plane but I believe you should make yourself familiar with the requirements.
It is believed that improper grounding can cause decreased milk production, and even some harm to cows. Other problems have been detected in horses. Will there be a concrete floor?
You can read the NEC online at http://www.nfpa.org/itemDetail.asp?categoryID=860&itemID=21227&URL=Publications/necdigest/Review%20the%20NEC¯%20online
You can read about the controversy at
http://www.mikeholt.com/newsletters.php?action=display&letterID=211
An AFCI will only protect the branch circuit that it feeds.
Now you can get two pole AFCI's that could, in therory, be used for a feeder to protect whole sub-panels including their branch circuits.
However, a quick look showed that they are limited to 15 and 20 amp devices.
OK, I stayed up longer than planned to read the sections about the equipotential plane. Can't claim to understand it all, but it appears to be a problem mostly with reinforced concrete structures. Is this correct? In my case, the stall flooring is expanded EVA (ethyl vinyl acitate) matting over earth. There is concrete on the other side of the barn, underlying the feed storage area and the tack room which are wooden, built on a floating slab. The barn itself is wooden.Shold I still be concerned, and if so, what's the solution?J
I redirect this to dutchblue.Really have not studied up on equipotential plane.
Joe, you will be fine. Sorry to get you all worked up, with the flooring you describe there will be no problems.
Well, that's good.
This whole business of the floor in effect becoming an electrode with a differential that causes current to flow is both interesting and disturbing, though. I wonder the implicatins for floating slab homes?
Edited 7/22/2006 1:37 pm ET by Joe Sullivan
There have been cases where that difference in potential coursing thru some champion racehorses have rendered them sterile.
Oh, dear.
Of course, many in the horse world have moved away from concrete stall floors for other reasons entirely (joint and feet, mostly -- think about how you feel working all day on concrete). Where concrete is used it normally has rubber or EVA over it, and shavings over that. Nevertheless, stall floors are wet places with lots of salts...
Actually, there never has been an especially good answer to floors for holding several hundred pounds of animal that produces many gallons of urine a day. Mats seem to be the best answer, but you have to pull them and dry out the floors once a year or so. We are doing that right now. It is a real joy, let me tell you.
I am thinking about having the earth dug out and replaced with a crushed limestone screening to underlie the mats. Someday. Not this year.