Question Regarding Conduit Fill.

[rickcola813]

I built a simple spreadsheet to help me assess conduit fill. I just ran into a conflict with an engineer. They are asking for us to pull 3 @ #2 AWG THHN conductors into 1" EMT. My spreadsheet shows that 3 @ #2AWG THHN conductors have a combined CMA of .3472 cubic inches. The spreadsheet also shows that the cross sectional area of 1" EMT is .864". When .3472 is divided into .864 I get 40.2%; which is greater than the 40% required. Am I calculating incorrectly or is it acceptable to round the answer up or down to the nearest number therefore making 40.2% acceptable?

 

[infinity]

According to Table C1: 1" EMT is large enough for 3-#2 THHN conductors. Although not an official part of the NEC the tables are fairy accurate for use when sizing raceways.

Welcome to the Forum.

 

[dkidd]

I built a simple spreadsheet to help me assess conduit fill. I just ran into a conflict with an engineer. They are asking for us to pull 3 @ #2 AWG THHN conductors into 1" EMT. My spreadsheet shows that 3 @ #2AWG THHN conductors have a combined CMA of .3472 cubic inches. The spreadsheet also shows that the cross sectional area of 1" EMT is .864". When .3472 is divided into .864 I get 40.2%; which is greater than the 40% required. Am I calculating incorrectly or is it acceptable to round the answer up or down to the nearest number therefore making 40.2% acceptable?

Notes to Tables
(7) When calculating the maximum number of conductors or
cables permitted in a conduit or tubing, all of the same
size (total cross-sectional area including insulation), the
next higher whole number shall be used to determine the
maximum number of conductors permitted when the calculation
results in a decimal greater than or equal to 0.8.
When calculating the size for conduit or tubing permitted
for a single conductor, one conductor shall be permitted
when the calculation results in a decimal greater than or
equal to 0.8.

 

[LarryFine]

According to Table C1: 1" EMT is large enough for 3-#2 THHN conductors.

Here, too: http://www.electrician2.com/rveltrain05/rf_calculator.html

 

[Rock86]

Looking at Annex C, it says 1" EMT. But if you use the information provided in Chapter 9, 1" EMT @40% is 0.346 in^2. (3) #2 THHN conductors is technically just over that number. Would the AHJ refer you to Ch.9 or Annex C?

 

[don_resqcapt19]

Looking at Annex C, it says 1" EMT. But if you use the information provided in Chapter 9, 1" EMT @40% is 0.346 in^2. (3) #2 THHN conductors is technically just over that number. Would the AHJ refer you to Ch.9 or Annex C?

Annex C is not enforceable code, just information.

The rules in Chapter 9 apply.

However the rules in Chapter 9 permit three 2AWG THHN in 1" EMT.

That is a result of applying Note 7 to Table 1 in Chapter 9. That permits the next higher number of conductors of the same size when the fraction is equal to or greater than 0.8. In this case the 40% area of the raceway is 0.333 square inches and the area of the conductor is 0.1158 square inches. When you divide 0.333 by 0.1158 you get 2.87, so Note 7 lets you round up to 3.

NOTE: I was not paying attention when I did this post...just looked at the first table that showed up for the area of the raceway, as that has been EMT in the past, however it is actually ENT and the area I used is not correct, however the area I used results in a good example for the round up provision of Note 7, to Chapter 9, Table 1.

 

[rickcola813]

According to Table C1: 1" EMT is large enough for 3-#2 THHN conductors. Although not an official part of the NEC the tables are fairy accurate for use when sizing raceways.

Welcome to the Forum.

Thanks for welcoming me in Robert. While I understand there are sources such as above and references such as Ugly's and the like, It is not unusual to have different sized conductors in one conduit, hence the need for my spreadsheet. Here is my rephrased question: When I calculate the allowable number of #2AWG THHN conductors in a 1" EMT conduit, my fill percentage came to 40.2%. In my world that is above the 40% allowed. Where am I wrong here? If the fill percentage is over 40% but under 40.5% is that why it is acceptable? Is someone allowed to round to the nearest whole number?

 

[LarryFine]

It is not unusual to have different sized conductors in one conduit, hence the need for my spreadsheet.

Check out the link I posted in post #4.

Here is my rephrased question: When I calculate the allowable number of #2AWG THHN conductors in a 1" EMT conduit, my fill percentage came to 40.2%. In my world that is above the 40% allowed. Where am I wrong here? If the fill percentage is over 40% but under 40.5% is that why it is acceptable? Is someone allowed to round to the nearest whole number?

Because you're calculating the quantity of conductors allowed in a given size of conduit, not the size of conduit required for a given quantity of conductors (although that really is what we need to deduce).

As Don pointed out in post #6, it's the quantity of permitted conductors that is allowed to be rounded up, not the size of conduit that may be rounded down.

 

[kwired]

Field experience says if this is short run and maybe only two 90 degree bends max - maybe is ok, especially if wanting to pull through something that is already existing.

Long run and/or up to allowed 360 degrees of bend - probably better to go next size on the raceway.

 

[Rock86]

Thanks for welcoming me in Robert. While I understand there are sources such as above and references such as Ugly's and the like, It is not unusual to have different sized conductors in one conduit, hence the need for my spreadsheet. Here is my rephrased question: When I calculate the allowable number of #2AWG THHN conductors in a 1" EMT conduit, my fill percentage came to 40.2%. In my world that is above the 40% allowed. Where am I wrong here? If the fill percentage is over 40% but under 40.5% is that why it is acceptable? Is someone allowed to round to the nearest whole number?

Following everyone's comment I figured I'd throw up some more math... hopefully a simplified enough..
(Note: Using 2020 NEC)
Table 4: 1" EMT area = 0.349in^2
Table 5: #2 THHN area = 0.1158
Notes to Tables #7: (Area of conduit) / (Area of conductor) = Number of conductors --> 0.349in^2 / 0.1158in^2 = 3.014 --> 3.014 is less than 3.800 therefore you are not allowed to round up and may have only (3) #2 THHN conductors in a 1" EMT conduit.
If you wanted to know about how many #1/0 THHN you could fit --> 0.349 / 0.1855 = 1.881 --> 1.881 is greater than 1.800 therefore you are allowed to round up to (2) #1/0 THHN conductors in 1" EMT conduit.

 

[infinity]

Following everyone's comment I figured I'd throw up some more math... hopefully a simplified enough..
(Note: Using 2020 NEC)
Table 4: 1" EMT area = 0.349in^2
Table 5: #2 THHN area = 0.1158
Notes to Tables #7: (Area of conduit) / (Area of conductor) = Number of conductors --> 0.349in^2 / 0.1158in^2 = 3.014 --> 3.014 is less than 3.800 therefore you are not allowed to round up and may have only (3) #2 THHN conductors in a 1" EMT conduit.
If you wanted to know about how many #1/0 THHN you could fit --> 0.349 / 0.1855 = 1.881 --> 1.881 is greater than 1.800 therefore you are allowed to round up to (2) #1/0 THHN conductors in 1" EMT conduit.

I didn't do the math but according to the table the bold part is incorrect. You're only allowed 1-#1/0 THHN in a 1" EMT, likely because the conduit fill for 2 conductors drops to 31%.

 

[Rock86]

I didn't do the math but according to the table the bold part is incorrect. You're only allowed 1-#1/0 THHN in a 1" EMT, likely because the conduit fill for 2 conductors drops to 31%.

Fair point... I was showing calculations which resulted over the .8.

So yes... after determining the results brings us to 2 wires, we would have to drop to 31% which would mean only (1) 1/0 THHN would be allowed. (Using 31% conditions now knowing only 2 conductors are allowed... .268/.1855 = 1.44 --> 1.44 < 1.80 = (1) 1/0 THHN)

 

[don_resqcapt19]

Following everyone's comment I figured I'd throw up some more math... hopefully a simplified enough..
(Note: Using 2020 NEC)
Table 4: 1" EMT area = 0.349in^2
Table 5: #2 THHN area = 0.1158
Notes to Tables #7: (Area of conduit) / (Area of conductor) = Number of conductors --> 0.349in^2 / 0.1158in^2 = 3.014 --> 3.014 is less than 3.800 therefore you are not allowed to round up and may have only (3) #2 THHN conductors in a 1" EMT conduit.
If you wanted to know about how many #1/0 THHN you could fit --> 0.349 / 0.1855 = 1.881 --> 1.881 is greater than 1.800 therefore you are allowed to round up to (2) #1/0 THHN conductors in 1" EMT conduit.

After I found the correct table, it shows 0.346 for the 40% fill area for 1" EMT in my code book. That will change your numbers. 0.346/0.1158 = 2.988. Still an example of the round up rule in Note 7.