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deko 09-08-2010 01:02 AM

How much conductor inside J-box?
This is probably a tired topic for some people, but I've heard different things and hoping to settle this.

As far as I know, NEC code states 6 to 8" of conductor in a J-Box. But measured from where? From where the sheathing ends inside the box? Measuring 0.25 to 0.5 inches of sheathing inside the box is easy enough, but do I measure the 6 to 8" of conductor from where the sheathing ends? Or from the edge of the box? For example, if the box is 3" deep, and I want to leave 7" of conductor, does that mean I have a TOTAL of 10" of conductor (7" extending beyond the edge of the box), or just 7" measured from where the sheathing ends inside the box?

Thanks in advance.

Just Bill 09-08-2010 05:56 AM

As a rough guide, I measure from the tip of the index finger to the wrist, 8-9".

AllanJ 09-08-2010 07:12 AM

The edge of the sheathing must be visible in the box and any clamping must firmly hit the sheathing. The minimum 6 inches is measured from the edge of the sheathing. If the box is deep you would want to leave more.

deko 09-08-2010 11:14 AM


The minimum 6 inches is measured from the edge of the sheathing.
That's what I thought. But now, after wiring a couple of boxes, I have another electrician telling me to measure from the outer edge of the box. With a 3" deep box, that makes my conductor leads 3" too short--enough to fail inspection!

Can anyone else confirm that conductor length in a J box is measured from the edge of the sheathing?

Jim Port 09-08-2010 12:43 PM

From the NEC.

300.14 Length of Free Conductors at Outlets, Junctions,
and Switch Points.
At least 150 mm (6 in.) of free
conductor, measured from the point in the box where it
emerges from its raceway or cable sheath, shall be left at
each outlet, junction, and switch point for splices or the
connection of luminaires (
fixtures) or devices. Where the
opening to an outlet, junction, or switch point is less than
200 mm (8 in.) in any dimension, each conductor shall be

long enough to extend at least 75 mm (3 in.) outside the opening.

deko 09-08-2010 01:09 PM

Thanks Jim.

To restate this in layman's terms:

A minimum of 6" of conductor inside the box, measured from where the sheath ends, with the caveat that the conductor extends a minimum of 3" beyond the outer edge of the box.

Jim Port 09-08-2010 02:06 PM

You got it as long as no dimension of the box is greater than 8".

deko 09-08-2010 02:34 PM

The boxes I'm working with are all standard residential stuff. Some are 3" deep. I started off stripping 7" of conductor but will go with 8" for rest of them.

Thanks for the help.

Scuba_Dave 09-08-2010 05:18 PM

I always use the deep boxes
So even with 6" it seems short
So I started doing 8"

frenchelectrican 09-08-2010 10:26 PM

mine SOP useally anywhere from 8 to 12 inches due the box size and how it will be confreaged espcally with ground wire I have to leave them little longer so I can able fold it neat.

Smaller box a little shorter but not any less than NEC code call for.

You do not want it super short otherwise you will cuss later when you try to change the devices I been there many time more than I care to count so please leave it at least 3 inches out or longer but NOT super long !


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