#6 Bend Radius

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FionaZuppa

FionaZuppa

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Part Time Electrician (semi retired, old) - EE retired.
anyone see any issue (NEC code or other safety issue) in having four #6 THHN in a 2.25" radius bend (1" plastic conduit). the bend is 180 degrees. its single phase 240v (two pole + neutral + gnd).

the wire seems to bend ok at this radius, but its definitely at the end of min radius.

is this doc generally accepted http://www.usawire-cable.com/pdfs/BENDING RADII AND PULLING TENSIONS.pdf
 
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hmmm, looks like conduit radius is the issue and not really an issue for the wire itself.

what about fittings? i have some 1" liquidtight fittings that are 2" radius (90 degree fittings). does the radius rule apply to fittings??
 
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FionaZuppa said:
hmmm, looks like conduit radius is the issue and not really an issue for the wire itself.

what about fittings? i have some 1" liquidtight fittings that are 2" radius (90 degree fittings). does the radius rule apply to fittings??
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The liquidtight fittings are a listed product and there is no minimum bend radius for them in the NEC. Also for conductors rated at 600 volts or less, I don't think that there is a minimum bend radius in the NEC.
There are rules about the minimum bending space required for a conductor termination, but not about the actual bend radius of the conductor.
 
don_resqcapt19 said:
The liquidtight fittings are a listed product and there is no minimum bend radius for them in the NEC. Also for conductors rated at 600 volts or less, I don't think that there is a minimum bend radius in the NEC.
There are rules about the minimum bending space required for a conductor termination, but not about the actual bend radius of the conductor.
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so oddly, why can a "fitting" be allowed to have 2" radius but a "conduit" cannot? doesnt make sense to me.

and to add, maximum allowable conduit fill is restricted. i shall see what my inspector says. thanks.
 
FionaZuppa said:
anyone see any issue (NEC code or other safety issue) in having four #6 THHN in a 2.25" radius bend (1" plastic conduit). the bend is 180 degrees. its single phase 240v (two pole + neutral + gnd).

the wire seems to bend ok at this radius, but its definitely at the end of min radius.

is this doc generally accepted http://www.usawire-cable.com/pdfs/BENDING RADII AND PULLING TENSIONS.pdf
Click to expand...

Does this fitting have a manufacturer and a part number?

Was this from the plumbing aisle?
 
FionaZuppa said:
so oddly, why can a "fitting" be allowed to have 2" radius but a "conduit" cannot? doesnt make sense to me.

and to add, maximum allowable conduit fill is restricted. i shall see what my inspector says. thanks.
Click to expand...

I think that the expectation is that for the largest single conductor that will fit under the fill rule, the conduit bend rule will take care of the bend radius of that wire or cable.
Obviously some things, like fiber optics, require special treatment under their installation instructions rather than the NEC.
You are allowed use a minimum bend conduit or minimum bend fitting, but there are some things you are not able to put inside it then. :)
 
FionaZuppa said:
so oddly, why can a "fitting" be allowed to have 2" radius but a "conduit" cannot? doesnt make sense to me. ...
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You don't normally pull near as much wire though a LFMC fitting as you would though a bend in a conduit.
The sidewall pressure is what damages the insulation of a conductor when pulled around a bend. The amount of this pressure is a function of both the pulling tension and the radius of the bend. It is expected that the pulling tension when installing a conductor in a flexible conduit fitting would be much less than where the conductors are pulled around a bend in the conduit system.
 
don_resqcapt19 said:
You don't normally pull near as much wire though a LFMC fitting as you would though a bend in a conduit.
The sidewall pressure is what damages the insulation of a conductor when pulled around a bend. The amount of this pressure is a function of both the pulling tension and the radius of the bend. It is expected that the pulling tension when installing a conductor in a flexible conduit fitting would be much less than where the conductors are pulled around a bend in the conduit system.
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the fitting itself is stiff nylon, not exactly as soft as plastic flex conduit.

in my case i am really not pulling wire through, the section of conduit is 10" on each side of the 180 with two 90degree fittings connected together to form the 180. its a very short section connecting a Siemens disco to a Eaton breaker panel, two metal boxes basically ganged together back-to-back. i will be making an assembly not unlike a pre-wired whip where one end is on disco and the other on the breaker box. flex conduit itself wont bend to a 2" radius, thus i need fittings to make the tight turn. i dont see any real safety issue, but codes are codes, etc. i guess an option is to use a conduit body to make the turn.

this is i mounted outside ~18" to bottom edge of lowest box. none of the punchouts align well so i needed a way to make this loop in a flexible manner. each end enters box in the vertical. i could enter the breaker box from the side but it will add much more stress on a 90degree fitting and it will be harder for me to bend wire into the box and then into final terminal location in the box, etc.

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