Fill Table Anomaly

[dkidd]

We ran across this yesterday.

From Chapter 9 Table 1, allowable fill for 2 wires is 31%.
From Chapter 9 Table 4, allowable fill for 1-1/2" is 0.631 square inches.

Given 2 4/0 THHN

From Chapter 9 Table 5, area of one conductor is 0.3237
Two conductors would be 0.6474

Therefore, two 4/0 would require a 2" EMT.

Annex C Table C.1 says that two 4/0 can fit in 1-1/2".

The amount of fill would be 31.8%.

Throw in a 6AWG THHN ground, the allowable fill is 40%, and a 1-1/2" works, with 34.3% fill.

 

[Dennis Alwon]

I have to run but I believe Annex C is based on 60% fill

 

[infinity]

We ran across this yesterday.

From Chapter 9 Table 1, allowable fill for 2 wires is 31%.
From Chapter 9 Table 4, allowable fill for 1-1/2" is 0.631 square inches.

Given 2 4/0 THHN

From Chapter 9 Table 5, area of one conductor is 0.3237
Two conductors would be 0.6474

Therefore, two 4/0 would require a 2" EMT.

Annex C Table C.1 says that two 4/0 can fit in 1-1/2".

The amount of fill would be 31.8%.

Throw in a 6AWG THHN ground, the allowable fill is 40%, and a 1-1/2" works, with 34.3% fill.

It's just the way the math works with 31% and 40% fill.

I think that Dennis meant 40% for Annex C.

 

[Dennis Alwon]

It's just the way the math works with 31% and 40% fill.

I think that Dennis meant 40% for Annex C.

Thank you-- I told you I was running out---LOL 40% is correct

 

[wwhitney]

We ran across this yesterday.

From Chapter 9 Table 1, allowable fill for 2 wires is 31%.
From Chapter 9 Table 4, allowable fill for 1-1/2" is 0.631 square inches.

Given 2 4/0 THHN

From Chapter 9 Table 5, area of one conductor is 0.3237
Two conductors would be 0.6474

Seems like Chapter 9, Table 1, Note 7 would apply: 0.631 / 0.3237 = 1.949, round up to 2.

Cheers, Wayne

 

[dkidd]

Thanks, that was the missing factor in my spreadsheet. I've got that incorporated now.

 

[Dennis Alwon]

You would think I remembered this since I made the new tables with corrections etc. I check my spreadsheet and yes it covers all situations. I spent a long time on that info and my brain forgot it all.... I'll blame it on old age and drugs.. not the drugs you are thinking about..LOL