# Thread: Correct conduit size calculation?

1. Senior Member
Join Date
Sep 2006
Location
Riverside, California
Posts
114

## Correct conduit size calculation?

I'm trying to figure out if I can use a 1 1/2" EMT instead of a 2" EMT for 4 #1/0 and 1 #6 ground based on these calculations. Instead of using NEC 2008 "Table C.1" I have calculated the maximum capacity of the1 1-1/2" conduit based on "Table 4". This table shows the maximum allowable percent fill on that particular conduit size. The following are my calculations. Please confirm if I am doing this correctly.
"Table C.1 Maximum Number of Conductors or Fixture Wires in Electrical Metallic Tubing (EMT)" on page #70-705 for THHN conductors it allows to install (4)#1/0 in a 1-1/2" or (7)#1/0 in a 2" conduit. Now refer to "Table 4 Dimensions and Percent Area of Conduit and Tubing (Areas of Conduit or Tubing for the Combinations of Wires Permitted in Table 1, Chapter 9)" on page #70-672. "Table 1" states that you are allowed up to 40% of the cross section of conduit and tubing for more than 2 conductors. Now referring back to "Table 4", for trade size 1-1/2" conduit we are allowed up to 0.814 square inch of fill in EMT. "Table 5 Dimensions of Insulated Conductors and Fixture Wires" on page #70-678 lists the approximate area of #1/0 THHN as 0.1885 square inch and #6 THHN as 0.0507 square inch. Using these approximate areas, we get the total approximate area of the #1/0 as 0.742 square inch for four conductors. The total approximate area of the #1/0 THHN plus the approximate area of the #6 THHN equals 0.7927 square inch. This total is below the 0.814 square inch as listed in "Table 4". Based on this calculation, am I still within code and can use 1 1/2" EMT instead of 2" EMT?
The reason why I ask if that I have stacked electrical rooms with very limited space and by using 1 1/2" EMT it should be easier to work with bends, etc.

2. Senior Member
Join Date
Jan 2007
Location
Yakima, Wash.
Posts
102
Your numbers, calculations and reasoning appear correct

3. Junior Member
Join Date
Apr 2009
Posts
1

## A littel guidens

AN EXISTING 3/4 TRADE SIZE RMC NIPPEL HAS 4 THHN CONDUCTORS AND ONE AWG 10 BARE GROUNDING WIRE HOW MANY ADDITIONAL AWG 10 THHN CONDUCTORS CAN BE INSTALLED? OKAY HERE IS MY QUESTION HOW DO I FIGUARE OUT HOW MANY COULD BE INSTALLED I KNOW HOW TO SIZE THE CONDUIT I UNDERSTAND THE PERCENT IS 60% FILL BECAUSE ITS A NIPPEL HOW DO I FIGURE HOW MANY MORE WIRES COULD BE INSTALLED WHAT THE STEP I WILL BE SO APPRICATE THE LITTEL GUIDENS:confused::confused:

4. Originally Posted by GERM80A
AN EXISTING 3/4 TRADE SIZE RMC NIPPEL HAS 4 THHN CONDUCTORS AND ONE AWG 10 BARE GROUNDING WIRE HOW MANY ADDITIONAL AWG 10 THHN CONDUCTORS CAN BE INSTALLED? OKAY HERE IS MY QUESTION HOW DO I FIGUARE OUT HOW MANY COULD BE INSTALLED I KNOW HOW TO SIZE THE CONDUIT I UNDERSTAND THE PERCENT IS 60% FILL BECAUSE ITS A NIPPEL HOW DO I FIGURE HOW MANY MORE WIRES COULD BE INSTALLED WHAT THE STEP I WILL BE SO APPRICATE THE LITTEL GUIDENS:confused::confused:
You should start another thread but here goes--- Go to the back of the NEC (Chapter 9-- Table 4) and look for the info on RMC conduit. Look up the sq. inches of the 3/4" size conduit at the 60% column. Now go to Table 5 and look up the area of #10 thhn. Now divide the area of the conduit by the area of the 10 THHN. This will tell you the total number of wires that would be legal at 60%.

5. Senior Member
Join Date
Jan 2008
Location
Northeastern PA
Posts
284
What size are the existing 4 THHN conductors?

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