Condit fill calculations

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crtemp

crtemp

Senior Member
Location
Wa state
I'm confused on the tables and annex c part of the nec.

Say I have the following....

All THHN in a schedule 80 pvc
#12 x10
#10 x5
#8 x3

Since I have over 2 wires in one conduit do I calculate the cross sectional area of the conduit at 40% and then add up cross sectional area of each wire and add them up and see what size the Will fit into?
 
First start on Table 5 ch9
find THHN row and use Approximate area square inches.
then add the total of all of the conductors of your example.

Then go to raceway properties Table 4 of ch9
Find rigid PVC conduit
scroll down the 40% column until you find a number that is higher than the total area that you calculated.
then look to the left of that row you will see what conduit is needed.

Added: Based on my calculation you need a 1.25" conduit
 
That's pretty much what I was thinking. Thank you for the clarification. Does the annex c take the 40% into consideration when it states the maximum number of conductors in any given raceway?
 
crtemp said:
That's pretty much what I was thinking. Thank you for the clarification. Does the annex c take the 40% into consideration when it states the maximum number of conductors in any given raceway?
Click to expand...
A

Annex C is only used when all the conductors are the same size with the same insulation. It is based on the table for 1 wire (53%), 2 wires(31%) or over 2 wires (60%)
 
Dennis Alwon said:
A

Annex C is only used when all the conductors are the same size with the same insulation. It is based on the table for 1 wire (53%), 2 wires(31%) or over 2 wires (40%)
Click to expand...

Corrected.

Essentially, it represents about 70% of the conduit diameter filled with cable, if you were to pack the cables as tightly as possible. Since two circles have a lousy packing factor in a circle, the area fill percentage is significantly less for 2 wires. 1 circle obviously has a 100% packing factor in a circle, so its area fill percentage is high. Then when you look at 3+ circles in a circle, the packing factor takes off to a steady cruising value between 80% & 90%.
 
crtemp said:
Wire totals to .2014 in sq and 3/4'' EMT is .213 in sq at 40%

Just want to make sure I'm not missing something.
Click to expand...

You are correct. It is less than 40%, but not by much, 37.79%
Personally it would depend on the length and number of bends, but I would go with 1".
 
tkb said:
You are correct. It is less than 40%, but not by much, 37.79%
Personally it would depend on the length and number of bends, but I would go with 1".
Click to expand...

Ya for sure. It was super tight when I physically looked at the pipe and wire. After all the parts to do it in EMT I said forget it and just ran 1-1/4" pvc. Much easier.
 
crtemp said:
I'm confused on the tables and annex c part of the nec.

Say I have the following....

All THHN in a schedule 80 pvc
#12 x10
#10 x5
#8 x3

Since I have over 2 wires in one conduit do I calculate the cross sectional area of the conduit at 40% and then add up cross sectional area of each wire and add them up and see what size the Will fit into?
Click to expand...

there's an app for that.....

fill.jpg
 
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