Minimun bending radius 600MCM THHN 480V

[mariocent]

The only NEC reference I've found for "Conductor Bending Radius" is only for 1000V (600V in earlier versions) or greater. (Part II. Requirements for over 1000 Volts, Nominal - 300.34 -Conductor Bending Radius.) I found a THHN spec from the site listed below, but the spec for the Mfg. of wire they're using only states:

"3.1.4 Minimum Bend Radius: Bends in Type THHN shall be made so that the cable will not be damaged." - https://www.southwire.com/support/THHNGuideSpecifications.htm

I found another Mfg. that states:

"3.1.3 Minimum Bend Radius: The minimum bending radius of THHN when training into final position (with no tension on the cable) should be 4 times the cable diameter for 14 AWG - 500MCM and 5 times the cable diameter for 600–750 MCM. When pulling through conduit (under tension) the minimum bending radius should be increased to 8 times the cable diameter for 14 AWG – 500 MCM and 10 times the cable diameter for 600-750 MCM."
http://www.cerrowire.com/files/file/THHN Spec Sheet.pdf

Is there such a specification that is concrete such as a UL rating specification for THHN? I am going to reject this 480V-800A switchboard install because the minimum bending radius of most of these conductors is probably less that 2-3x Max the diameter of the conductor. I would just like a more solid reference to justify my rejection.

 

[roger]

I don't see a problem in the picture and by Cerrowire's statement using the word "should" seems to be a non issue, if they were serious they would have used the word "shall".

Roger

 

[jeremysterling]

I have no objection to the pictured install. I would prefer the bends to be just a tad tighter to maintain the neat bundle.

I've never understood the prejudice against bending building wire. After all, its stranded and insulated with flexible material.

 

[JFletcher]

I also don't have a problem with the pictured install. If the wires are bent to the point where it is distorting the jacket / insulation, then it's probably too tight.

There are probably billions of switch boxes and receptacles with 12 and 14 gauge wire practically folded in half that last for 40 50 60 plus years with no problems. Not that I would run 600 MCM that tight...

Eta : the OD of 600 MCM is a little more than an inch...5x that would be 5.1" radius, or about 10.25" diameter. If you are going to fail the installation based on the conductors being bent too much, I'd suggest you carry a plastic protractor with you to extrapolate the bends.

10" is roughly the size of a dinner plate.

and based on what is pictured, if you were to fail that, it should take somebody about 2 minutes to straighten the wires out enough to no longer be over bent

 

[infinity]

There is nothing wrong with the bends in the photo.

 

[MasterTheNEC]

The only NEC reference I've found for "Conductor Bending Radius" is only for 1000V (600V in earlier versions) or greater. (Part II. Requirements for over 1000 Volts, Nominal - 300.34 -Conductor Bending Radius.) I found a THHN spec from the site listed below, but the spec for the Mfg. of wire they're using only states:

"3.1.4 Minimum Bend Radius: Bends in Type THHN shall be made so that the cable will not be damaged." - https://www.southwire.com/support/THHNGuideSpecifications.htm

I found another Mfg. that states:

"3.1.3 Minimum Bend Radius: The minimum bending radius of THHN when training into final position (with no tension on the cable) should be 4 times the cable diameter for 14 AWG - 500MCM and 5 times the cable diameter for 600–750 MCM. When pulling through conduit (under tension) the minimum bending radius should be increased to 8 times the cable diameter for 14 AWG – 500 MCM and 10 times the cable diameter for 600-750 MCM."
http://www.cerrowire.com/files/file/THHN Spec Sheet.pdf

Is there such a specification that is concrete such as a UL rating specification for THHN? I am going to reject this 480V-800A switchboard install because the minimum bending radius of most of these conductors is probably less that 2-3x Max the diameter of the conductor. I would just like a more solid reference to justify my rejection.

There is no minimum maintained bending radii for individual conductors when they are 1000V or less, except at terminations as expressed in 312.6(A) and (B), where applicable. Once you get over 1000V then you have some guidance in section 300.34 in regards to the NEC®. When it comes to 1000V or less then as stated already by the manufacturer, use the values they provide for you from their codes and standards teams. They are better equipped to tell you the specific details about their products.

If the insulation is not noticeably damaged then why would you have a concern? I can promise you that bending larger conductors excessively would result in insulation damage well before potential conductive media damage. However, if you did have a concern it would be acceptable to ask them to reach out to the manufactures for additional information if you deem that needed. However, based on the information you provided I would say there is no issue where as these bends are simple deflection bends and would not pose an issue to the conductors conductive material or the protective insulation.

You have to ask yourself, if you can't justify it then you shouldn't be failing it.

Just my thoughts on the subject.

 

[Jraef]

Besides, that’s not a “bend”, that’s an “offset”.

There’s nothing that says you can’t bend a conductor at a hard 90, it’s done all the time inside of gear. What you can’t do is damage the insulation or significantly change it’s thickness. The manufacturer recommendations are based on that last point because if you compress the insulation too much, it can reduce the dielectric strength of it and could lead to failure. Everyone’s formula for the PVC they use is a little different, so they will test it and make their recommendations. But it’s only a recommendation, not a rule. If it was installed in a piece of gear then tested and passed, it’s goid to go.

 

[kwired]

... What you can’t do is damage the insulation or significantly change it’s thickness...

And within a cabinet where the conductor is possibly in free space at the point in question - is even less of a concern then when that possibly compromised insulation is laying against a metal wall or partition. Last one I recall seeing that was factory assembled is a Milbank meter socket with main breaker and loadcenter. The factory installed conductors between meter and main breaker were bent pretty sharply - insulation integrity maybe a little questionable - but was also located where if there were no insulation on it at all it really wouldn't matter much.