Section 17.2.5 of NFPA 921-2004 added the subject of electrical arc surveys without providing much information on what it means and how to interpret it. Below I have written what I believe at first blush are the fundamentals of arc pattern analysis. Please provide any further insight you can give on this topic:

Fundamentals of arc pattern analysis:

1. Electrical arcing can only occur in an energized wire.
2. The severing of an electrical wire by melting either by arcing or from the heat of the fire, de-energizes that branch circuit from the location of the severing, to the load, so no further arcing can occur in that portion of the subject branch circuit.*
3. Because of that, multiple arcs resulting in the severing of the conductors in a particular branch circuit, must occur in the order from the location furthest away from the source of power to the location closest to the source of power.
4. Thus, multiple arcing locations on a single branch circuit with at least one arc severing location, may be used to define the sequence of the arcing incidents and thus, the direction the fire progressed in the area traversed by the particular branch circuit.
5. Electrical arcing (with or without complete conductor severing) may also trip the over-current protection device (or OCPD such as circuit breaker, fuse, etc.) rendering all of that particular circuit de-energized and thus no further arcing can occur anywhere on that branch circuit.
6. Tripping of the over-current protection device de-energizes every circuit power through that same OCPD.

* a rare exception that must be considered is circuits powered from two separate sources

Thanks for your input.

Michael A. Learmonth, B.A.Sc., M.B.A., M.Eng., J.D., LL.B., C.F.E.I., P.Eng.
Senior Associate, Giffin Koerth Forensic Engineering and Science
40 University Avenue, Suite 800
Toronto, Ontario, Canada M5J 1T1
Phone: 416-368-1700 ext. 225
Fax: 416-368-5576