Section 90.7 requires the inspector to judge suitability of an installation based upon the listing of the equipment and the installer's adherence to the instructions that accompany a listed product. In other words: instructions must be followed.
Conductors and wiring lugs are listed, and therefore must be installed according to that listing. The instructions will typically require stripping the insulation to a minimum exposed comnductor, sometimes a termination compound and sometimes a torquing range for the connection.
Also, Article 110.14(A) requires "Connection of conductors to terminal parts shall ensure a thoroughly good connection without damaging the conductors..."./
All of which means most inspectors will interpret that all the wire strands need to be under the same lug, as lugs are rated for a particular wire size, not for some of the strands.
but ive heard most current travels on the outer part of the wire so by splitting the wire on the bus would change the current flow and characteristics of the wire(ohms) and actually over heat that percentage of wire. this is my humble opion based on what ive heard and interpting therory. keeping in mind im just throwing my hat in the ring or putting in my two cents. H2o
The ampacity of wire at 60Hz is driven more by the temperature rise the insulation sees. Not skin effect. If you have stranded wire with 7 strands (one in the center, 6 outside) the strand in the middle has no easy way to shed the extra heat, as it's surrounded by the other strands that are also getting hot. So you can't just add up the ampacities of the individual strands ("Looks like 12 guage wire, so that's 20 amps times 7"). It's less than that. But you will see less voltage drop at the rated ampacity then what you'd see if it were valid to add the ampacity of the individual strands.
Skin effect is just gee whiz info at 60hz unless you are in the megawatt arena. It sure has nothing to do with any wire you can pick up a roll of.
I am confused by this statement. I learned that current flows on the outside of wire w/ alternating current (skimming affect) Whether it be solid or sttranded the current will flow on the outside of the wire.
A person asked about spliting the stranded wires and we got a crazy response regarding ampacities and " of wire. Answer should of been put all wire in same lug! When I see electricians who split stranded wire because it doesnt fit, I would like to smack them.
Remember in the code it also states "good workmanship" This is all to often ignored.
Re: all strands under one lug or terminal
#164909 06/13/0710:35 PM06/13/0710:35 PM
Bob answered the question up at note 2. Lugs are listed for acceptable sizes. I was just renforcing what Ghost man was saying. IBM used a lot of 400 hz and some young engineer type guys started spreading the same hooey about how skin effect certainly should be a factor at 400hz and we should be using fine stranded wires for the 400hz cables. They did it under the covers and behind the customer plug but once we started talking to the electricians that same listing problem raised it's ugly head. Regular lugs are not listed for fine strand wire. Then a saner head prevailed in Kingston and ran those same skin effect formulas on 400hz and figured out it would not be a factor for the normal stranding you have in THHN. Anecdotally I can say the fine stranded wire in the IBM cable ran about the same temperature as the THHN. The good side was, when we removed these systems everyone got battery cables for their boats and jummper cables for their cars when we "recycled" those cables