NM-B Sheathing Maximum Projection Into Panel/Cabinet?

Status
Not open for further replies.
C

CuriousHomeInspector

Member
Location
Little Rock, AR, USA
Is there a stated maximum distance that NM-B sheathing can extend into a panel/enclosure. I often see NEC 341.17(C) (outdated/moved I believe)cited as giving a minimum of 1/4" (although I thought this was for conduit and boxes, not panels). I have never seen a maximum listed in the NEC but I've had many claim that it is a 1/4" minimum, and anywhere from 1/2" to 1" maximum

Even the textbook references for home inspector education states that the sheathing should be cut far back to prevent adding fuel to a panel fire and to prevent build-up of heat in the wires (which I think is bunk).

Any insight to an actual maximum (within the realms of maintaining workability) and why with reference?
 
There is no NEC maximum limit or length. In a breaker panel, I have seen a few inches of sheathing or jacket entering the panel, usually with field applied markings on that portion. I would consider that a maximum workable limit. And junction boxes, about three quarters of an inch is all I would want.

The code minimum as you wrote is a quarter inch. I would presume this is so that any clamps will clamp the jacket and not wires.
 
CuriousHomeInspector said:
Is there a stated maximum distance that NM-B sheathing can extend into a panel/enclosure. I often see NEC 341.17(C) (outdated/moved I believe)cited as giving a minimum of 1/4" (although I thought this was for conduit and boxes, not panels). I have never seen a maximum listed in the NEC but I've had many claim that it is a 1/4" minimum, and anywhere from 1/2" to 1" maximum
Click to expand...

Where is the 1/4" minimum on the NEC? There is no maximum.
 
Thank you for the replies.

I agree whole heartedly that 314.17(C) that is often quoted for this is improper for cabinets as that section is for Conductors Entering Boxes, Conduit Bodies, or Fittings. However this is cited (I believe erroneously) in "Code Check" books as giving a minimum projection of sheathing into a panel as 1/4" and the maximum of 1"

To me the appropriate section is 312.5(C) which is Cables entering cabinets, cutout boxes, and meter socket enclosures.

Really what (C) says is Cables. Where cable is used, each cable shall be secured to the cabinet, cutout box, or meter socket enclosure.

To me this means that the NM-B connector needs to be on the CABLE, not on the conductor insulation. Without a minimum, without a maximum.

There is an exception below which I think confuses many people that cables with nonmetallic sheaths can enter the top of a surface-mounted enclsoure through one or more nonflexible raceways not less than 18" and not more than 10 ft in length provided many conditions are met, including that the cable sheath is continuous through the raceway and extends into the enclosure beyond the fitting not less than 6mm (1/4).

The 1/4" only applies in the case using the exception in my opinion.

I am not an electrical engineer, nor an electrician. However the arguments I hear on this are fire fuel, wires overheating, etc. I think all of this is bunk due to the higher rating of the conductors themselves in NM-B cable (which I realize cannot be stripped out and used individually as higher temp conductor due to lack of marking) which is derated as a cable and the fact that the required flame retardant qualities of NM-B cable. But I digress as I am not an electrical engineer and not practicing electrical engineering.

What irks me is that there is a respected electrician and books out there that are misinforming home inspectors who are parroting this information and are probably rightly pissing off electricians.

Now one of the electricians has come back and said the sheathing projection shall be 1/4" - 1/2" into panel as per 110.3(B) Manufacturer's instructions. I've never seen that in manufacturer instructions. Has anyone else????
 
There is no NEC requirement to extend the insulation 1/4" or any other distance past the connector in a panel.

CuriousHomeInspector said:


Now one of the electricians has come back and said the sheathing projection shall be 1/4" - 1/2" into panel as per 110.3(B) Manufacturer's instructions. I've never seen that in manufacturer instructions. Has anyone else????
Click to expand...


No and even it you could find one it only apply to that manufacturers connector.
 
no maximum length

no maximum length

CuriousHomeInspector said:
Thank you for the replies.

I agree whole heartedly that 314.17(C) that is often quoted for this is improper for cabinets as that section is for Conductors Entering Boxes, Conduit Bodies, or Fittings. However this is cited (I believe erroneously) in "Code Check" books as giving a minimum projection of sheathing into a panel as 1/4" and the maximum of 1"
Click to expand...


314.17.C states 1/4" but there is no maximum length listed in the code. If an inspector calls you on this ask him/ her to show you where. In my state the inspector is required to cite the code when writing up a problem. I leave my coverings on and write what the cable feeds on the jacket with a fine point sharpie.
 
Status
Not open for further replies.
Top