Bending diameter.

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cudahlr68

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A coworker came to me and asked about the bending radius of romex and how to calculate it. 334.24 says it should not be less than five times the diameter
of the cable. On flat cables such as 14-2, 12-2 would you measure the overall width accross the cable as the diameter? or is there another method?
 
Yes. I would consider the largest dimension of the flat cable to be the diameter. Many installers will bend cables to nearly a 90? angle around corners or when deflecting the cable from a vertical to horizontal run. While this looks very neat and workmanlike, it is likely a violation. A typical 14/2 thru 10/2 NM cable needs an approx. 2.5 in radius curve in order to comply with this section.
 
I agree with Bryan

I suggest picturing a keyless (or keyed porcelain) lamp holder if the bend of cable follows the curve it is probably OK. Also I have viewed RX horizontal through a bored hole in studs and bent at a sharp angle to change elevation. The stuff is not pipe. I suggest that you need to atleast get your hand between the stud and the cable.

just a thought
 
just bend it. ever see how bent in half even the old clothe wiring gets in these ole boxes and will still out live us.

merely a guide line.


I think the best is paralled conductors... eg. to be the same length.. I remember 28 some years ago, cut in some paralled 500's, one group was a bit longer (because I made them the same length), I felt it looked good and was right. My boss at the time had me cut them back to look the same, cut back on both ends took about 3 feet off. Whats up with that.... I try to keep them the same length but it seems no one else does so .....


bent wires,shorter parrelled conductors, lions and tigers and bears,,oh my.

r
 
How many other code requirements do you feel are "merely guidelines"?

"No one else cares, so why should I"... This is the attitude that is perpetually damaging our industry generation to generation. It's not a bad thing to care and take the higher road, even though it is also the harder road. Sticking to a set of principles is rewarding in the long run...
 
My apologies on the "merely a guidline" crack.

I do have alot of respect and pride in what I do .


Thank you for reminding me.
 
bphgravity said:
...Many installers will bend cables to nearly a 90? angle around corners or when deflecting the cable from a vertical to horizontal run. While this looks very neat and workmanlike, it is likely a violation....
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Bryan, when you write this up for multiple violations on the same inspection, do you say the bending radii has been exceeded like I do?
It always makes me smile when I use the word "radii". :D
 
Should the assumption be made that the reason for the bending radius limitation is so the conductors are not severely bent causing stress and potential damage to them? ................Or is it so the electrons can flow more freely through a less resistive sweeping bend? <JOKE>
 
ritelec said:
just bend it...merely a guide line...I felt... Whats up with that...seems no one else does so ...bent wires...oh my.
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Wouldn't it be nice if there was a remote control that we could use to rewind some of the stuff we say and change it??? Hmm. That would make a good movie!:grin:
 
cudahlr68 said:
A coworker came to me and asked about the bending radius of romex and how to calculate it. 334.24 says it should not be less than five times the diameter
of the cable. On flat cables such as 14-2, 12-2 would you measure the overall width accross the cable as the diameter? or is there another method?
Click to expand...

I guess that would depend on which way you were bending the wire. On the flat or on the edge. :)
 
racerdave3 said:
Should the assumption be made that the reason for the bending radius limitation is so the conductors are not severely bent causing stress and potential damage to them?
Click to expand...

No, I don't think so.

The reason I say that is because for conductors under 600 volt there is no minimum bending radius (or radii as the case may be ;)) You can put a sharp 90 turn in a single 500 kcmil. Its only cable assemblies that are limited'

IMO this minimum bending requirement has more to do with damaging the cables outer sheath. I am guessing that requirement went into the code along time ago when NM was much more fragile. I don't regularly bend sharp 90s in NM but I have also not seen damage from the actual bend if I do it.


................Or is it so the electrons can flow more freely through a less resistive sweeping bend? <JOKE>
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No thats not it, if the turn is to sharp the electrons fall off the wire. ;)


BTW, with some types of grounding sharp corners are prohibited as they can lead to problems.
 
I don't really use this "NM" stuff, but why would you use the long side as the diameter if you are bending the flat side?
Don
 
No thats not it, if the turn is to sharp the electrons fall off the wire.
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That actually happens with lighting protection system conductors. Too sharp of bend may result in a "side strike"...the lighting jumps off the conductor to another grounded object.
Don
 
don_resqcapt19 said:
That actually happens with lighting protection system conductors. Too sharp of bend may result in a "side strike"...the lighting jumps off the conductor to another grounded object.
Don
Click to expand...

It is also an issue to the manufacturers of TVSS units.
 
don_resqcapt19 said:
I don't really use this "NM" stuff, but why would you use the long side as the diameter if you are bending the flat side?
Don
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I agree with you Don.

Take a section of 10/3 UF cable, that is about 1/2" thick by 1 1/2" wide.

If I am bending it on the flat (Like I have a choice ;)) why would I care it is 1 1/2" wide. This is not the same as figuring cable size for pipe fill.

Using the overall diameter would mean that a flat 10/3 UF would have a bending radius of 7.5 inches. That is IMO ridiculously excessive.
 
Never in my 25 years of wiring has an inspector said anything about my 90's.Here in FL many homes are block with 3/4 inch strips of wood to fasten drywall.Given that limited space we must make sharp bends in outside corners.Only other way is to make 2 90's as if it was emt.Has there been any problems over this ?
 
racerdave3 said:
Should the assumption be made that the reason for the bending radius limitation is so the conductors are not severely bent causing stress and potential damage to them? ................Or is it so the electrons can flow more freely through a less resistive sweeping bend? <JOKE>
Click to expand...

I know its a joke but I think the down conductors on lighting rods are required to have no bends.....so electrons can flow freely or something...heck i don't know.
 
Jim W in Tampa said:
Here in FL many homes are block with 3/4 inch strips of wood to fasten drywall.
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Jim how do you protect the NM from nails or screws and meet the required 11/4 in of article 300.4(A)(1)
 
iwire said:
If I am bending it on the flat (Like I have a choice ;)) why would I care it is 1 1/2" wide. This is not the same as figuring cable size for pipe fill.
Click to expand...

I think that's exactly what's happening - people are dragging the rule for determining the diameter for pipe fill (Note 9 to Tables, in Chapter 9) to the section requiring the "five-times" bending rule in 334.24.

There really isn't substantiation for that idea, IMO. I'd never really thought about it until just now. :cool:
 
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