What about the 60% maximum fill rule?

I use straws in the class room but any round objects will work.
I have the students grab a hand full of straws and tighten up their grip close to the end.
Looking at the group of straws one can see the space between the straws.

On motor control centers I have filled nipples as full as I could possibly get them and do the math and it wouldn’t be close.

38 #12THW conductors fill an 1 1/2 inch EMT to 40%
97 would be 60% but I would bet it couldn’t be done or let me say I couldn’t get then in there

I see your point, you’re speaking from a practical perspective not a code perspective. Given your example you’re saying that most would be unable to physically install an excess of 60% in a nipple not that the requirement would actually permit more than 60% fill.

As with anything it could be over filled if one used a lot of large conductors mixed with small conductors but it would be hard to do and impossible in a residential setting


I wrote a Conduit Fill Calculator that allows mixing as many as 30 different conductor sizes and types. The total number of conductors is not limited. The calculator will give the total fill as a percentage for 30 common conduit types.

The calculator is free to my students and to InterNACHI members. Feel free to use it and give it to your students if you are interested.

I do appreciate this and have searched your site to no avail. Could you please help me to find it with a link

The question wasn’t asked of me. But I always thought that panels were not to be used as raceways. In rereading the article, I guess it’s the “unless adequate space for this purpose is provided” that makes it OK. I guess we would have to see inside to know if it was OK as-is.

Please splain me if I am mistaken.

With 312.8 you cannot possibly exceed the 75% fill for taps and splices even if you tried. :slight_smile:

Scroll down.


Just an observation: It seems that the verbiage chosen for that article is a bit inconsistent. All of the other references to the 40 or 75% fill I looked at are in the context of what IS permitted. The article might just as well state that they MAY be used for… as long as adequate space for this purpose is provided. The conductors shall not fill the wiring space at any cross section to more than 40 percent of the cross-sectional area of the space, and the conductors, splices, and taps shall not fill the wiring space at any cross section to more than 75 percent of the cross-sectional area of that space.

Their use of the phrase “shall not be used” seems inconsistent when they really MAY be used for those purposes, provided they meet certain criteria.

Shall not “unless”

Notice “unless” is also used


Thanks for posting the link. Use this one instead: http://www.bestinspectors.net/NACHIGL/free.htm

It has a few more things on it. The Conduit Fill Calculator is near the bottom. As with all my electrical calculators, it is intended to be used for training purposes.

I thank you and I will take the liberty of saying thank you for the many that will use it.