DIYbanter - View Single Post

Tom Horne, Electrician

George E. Cawthon wrote:
wrote:

Why would sharp bends do anything? As long as the wire is continuous
the electrons will flow whatever shape the wire is.

I had someone tell me that making sharp bends in romex was bad too.
Thats bull****. Electricity follows the copper. Bends dont matter.
When I wire something I always like to make it look neat bu bending
the wires around corners and keeping the bends tight to the structure.

you create future fail spots, the bend stresses the metal and has a
good chance of it cracking or similiar in the future. cracked wires
overheat and cause fires

I agree you shouldn't bend it to tight like a near perfect 90 degrees
but you don't need to bend it that much to get good looks. Bending
copper work harden it and further bending operations can make it break,
but exactly how many bends before it breaks. When you wrap a 12 gauge
wire around a post, tighten down the screw, and bend the tail to make it
break off, how many bends (back and forth motions) do you make? For me
it is at least four each way at a very sharp angle. But when you
install romex, you bend it and then how much additional bending do you
do, and how sharp are the bends compared to a single stripped wire? My
guess is that you would have to do a lot of very sharp bending to get
the wires work hardened enough to crack.

When the acceptance testing was done on type NM cable by Underwriters
Laboratories; low these many years ago; the incidents of conductor
insulation damage went up sharply at bend radii of 3 cable diameters.
The US NEC requires bends of five cable diameter in radius as a safety
margin. The problem isn't conductor fracture but rather that the
insulation will fail over time if it is bent too sharply. Since there
is a bare EGC run inside the jacket of type NM cable the possibility of
arcing which can cause a fire is real.
--
Tom Horne

"This alternating current stuff is just a fad. It is much too dangerous
for general use." Thomas Alva Edison