How many #12 THHN allowed in 3/4" conduit

Ran across 3/4" with 14 #12 THHN in 3/4 " conduit.

I believe 18 I dont have the book near right now

OK, Thanks, it just looked like a lot, and I cant remember.

Jeff using the link below I was incorrect. 16

Might be how many will fit in the conduit itself…which is probably from the table in the back of the NEC. However, when we stuff a conduit we need to take another important thing into consideration…A few other adjustments could be needed but I am sure someone more knowledgeable than me will elaborate.

Paul, nice to see you here and helping.
Hope you are doing well.
I wish I could say I am more knowledgeable than you, but that is not going to happen in the electrical field for me buddy. ha. ha.

Thanks for coming over.

Marcel :):smiley:

Terry, great link, thanks, it’s a keeper.

It seems to me there could be some consideration for deration…but that’s just a guess.

I can’t find what I was looking for on this board, but “bundling” was discussed several months ago.

Bundling is a collection of wires that pass through a conduit together, such as described in this thread. Heat dissipation is difficult when many (I don’t remember how many) wires are bundled. Over-heated wires have a lower ampacity (I have a chart for that somewhere, but I can’t find it my library for some reason), which can affect electrical service in a residence.

I hope somebody who knows this about stuff can produce the needed charts to help us discuss this.

While many people simply run to the chart in the back of the NEC for how many wires can be in a conduit. They forget the other factors that dictate the real world senerio. In deed you would need to take into account the situation of current carry conductors and ampacity adjustments and so on as well as possibly ambient temperature changes that can effect the ampacity ratings as well.

It is simply not an issue of looking at a chart and being a cure all, it may assist in the capacity fill arena but we have to consider many factors when pulling conductors within a conduit or tubing.

(2) Adjustment Factors.
(a) More Than Three Current-Carrying Conductors in
a Raceway or Cable. Where the number of current-carrying
conductors in a raceway or cable exceeds three, or where
single conductors or multiconductor cables are stacked or
bundled longer than 600 mm (24 in.) without maintaining
spacing and are not installed in raceways, the allowable
ampacity of each conductor shall be reduced as shown in
Table 310.15(B)(2)(a). Each current-carrying conductor of
a paralleled set of conductors shall be counted as a currentcarrying

[FONT=Times-Bold][size=1]Table 310.15(B)(2)(a) Adjustment Factors for More Than
Three Current-Carrying Conductors in a Raceway or Cable
Number of Current-Carrying Conductors Percent of Values in Tables
310.16 through 310.19 as Adjusted for Ambient
Temperature if Necessary
4–6 80%
7–9 70%
10–20 50%
21–30 45%
31–40 40%
41 and above 35%

Now we also have to look at temperature adjustments…if needed…using Table 310.16 Ambient Factors Adjustments called Correction Factors.

Anyway…it is not always just using the tables at the back of the book to CRAM a raceway…we gotta know the MATH involved.

Of course we are then reminded of the following statements…

**(D) Small Conductors. **Unless specifically permitted in
240.4(E) or 240.4(G), the overcurrent protection shall not
exceed 15 amperes for 14 AWG, 20 amperes for 12 AWG,
and 30 amperes for 10 AWG copper; or 15 amperes for
12 AWG and 25 amperes for 10 AWG aluminum and
copper-clad aluminum after any correction factors for
ambient temperature and number of conductors have
been applied.


Paul, Thanks, This was a apartment building with u-grades, all small load micro wave, dishwasher, lighting, the only 2- I may have a concern would be the 2- A/C outlets,

Tell me something…

Why is it that excessive bundling of conductors is not allowed by NEC, but they will allow an excessive amount of conductors stuffed inside a conduit?

Branch wiring will conduct heat either way.

They Dont…read my post…It refers to CCC in a conduit or tubing as well as the bundling issue.

The table is for Conduit Fill…Not Adjustments I posted

When I come across excessive bundling, I refer to a licensed electrician–with the caviat the buyer have the electrician sign-off on his letterhead, signature, and his license number.

Of course, I explain to the buyer what may or may not occur…