I cannot remember what is the maximum of romex insulation allowed in a service panel. I was thinking less than an inch, cannot find anything to support my thinking. A service panel today had 5-7 inches of romex insulation left on the circuits.
The NEC has no maximum length that NM cable can enter a panelboard. The closest thing you might find is Electrical equipment shall be installed in a neat and workmanlike manner which is, IMO unenforceable.
Thanks Robert!
IMO excessive cable sheathing inside a panel it’s a sign of poor workmanship or Harry Homeowner wiring. Red flags go up when I see that.
In all the literature I have read most say no more than one inch
This is considered “best practice,” but there is no requirement that limits the amount.
IC good to know. I have been calling it up, maybe I should’nt be.
No different in the panel than when it is in the wall. You are however required to have 6" of free conductor inside the box.
BTW, the minimum required by the NEC is 1/4" inside the panel or box.
Jim, where are you finding this 1/4" minimum requirement in the NEC for NM cable?
© Nonmetallic Boxes and Conduit Bodies. Nonmetallic
boxes and conduit bodies shall be suitable for the lowest
temperature-rated conductor entering the box. Where nonmetallic
boxes and conduit bodies are used with messengersupported
wiring, open wiring on insulators, or concealed
knob-and-tube wiring, the conductors shall enter the box
through individual holes. Where flexible tubing is used to
enclose the conductors, the tubing shall extend from the last
insulating support to not less than 6 mm (1⁄4 in.) inside the
box and beyond any cable clamp. Where nonmetallicsheathed
cable or multiconductor Type UF cable is used,
the sheath shall extend not less than 6 mm (1⁄4 in.) inside
the box and beyond any cable clamp. In all instances, all
permitted wiring methods shall be secured to the boxes.
Exception: Where nonmetallic-sheathed cable or multiconductor
Type UF cable is used with single gang boxes
not larger than a nominal size 57 mm × 100 mm (21⁄4 in.
× 4 in.) mounted in walls or ceilings, and where the cable
is fastened within 200 mm (8 in.) of the box measured along
the sheath and where the sheath extends through a cable
knockout not less than 6 mm (1⁄4 in.), securing the cable to
the box shall not be required. Multiple cable entries shall
be permitted in a single cable knockout opening.
I’m not seeing how that would apply to NM cables entering a panel.
Cable clamps would be used as the cable enters the box and I would consider the enclosure a box also.
314.17© is only for Nonmetallic Boxes and Conduit Bodies.
I see your point about this only stating NM boxes. I don’t see why it would not apply to metallic boxes or where cable clamps are used on metallic boxes, but don’t know if I could find words to support it. 314.17(B) leaves out NM-B when talking about metallic boxes. IMO the same requirements should apply even tho it is not specified. After all why would it be allowable for the sheath not need to extend past the clamp if a metal box is used but use a non-metallic box and now it must extend 1/4" past the clamp?
After reading that section a few more times IMO it only applies to plastic boxes that are used with messenger-supported wiring, open wiring on insulators, or concealed knob-and-tube wiring. Standard NM installation would not even apply.
See the following:
312.7 Space in Enclosures. Cabinets and cutout boxes shall have sufficient space to accommodate all conductors installed in them without crowding.
Check the blue text I highlighted in (C).
I see your point but I don’t agree that it says that the way that it’s written.
Yes, that is one of installations types (NM cable) permitted to be used when using messenger-supported wiring, *open wiring on insulators, or concealed knob-and-tube wiring. *The way I read it it says:
When using messenger-supported wiring, open wiring on insulators, or concealed knob-and-tube wiring with several different wiring methods:
1-Where **flexible tubing **is used to enclose the conductors, the tubing shall extend from the last insulating support to not less than 6 mm (¼ in.) inside the box and beyond any cable clamp.
2-Where nonmetallic-sheathed cable or multiconductor Type UF cable is used, the sheath shall extend not less than 6 mm (¼ in.) inside the box and beyond any cable clamp.
These three installation methods Flex, NM and UF all revert back to clarify the original installation of messenger-supported wiring, open wiring on insulators, or concealed knob-and-tube wiring.
*
I’m not sure if that is the intent of this section but that’s how it’s written. 
*
I see it as when NM-B is used the condition applies as well as for K&T, messenger supported etc. The difference is that individual holes are not required to be used with NM.