Conflicting Info Regarding Ampacity of Wires

[Smatthew 219]

So the first pic is from a text that I have for an apprenticeship and the other is from the NEC 2008 code book. I hope they appear in the post. If not please view under post (I'm new to the site).

The text shows that it's "OK" to run 300 amps through 2/O wire, 405 through 4/O, etc. without specifying what type wire it is. But as far as I can tell from the NEC code that is way off, no matter the type.

NEC says that only 260 through the most tolerant type 4/O and 190 through 2/0 wire. :?

Can anyone explain this discrepancy and/or if this is a common occurrence....the NEC and other sources being so out of sync with one another?

Many Thanks for any Answer.

Smatthew

 

[JFletcher]

The first cable is Type SC, which gets such high ampacities by using High strand count wire, and insulation that is rated to 105* C. I had to look it up, apparently is used for temporary installations for things like stage lighting. As far as I can tell, it is not an NEC approved chapter 3 wire type, so it cannot be used in permanent installations.

Picture number 2 from the 2008 NEC is for approved wiring types like xhhw. Although they can be de-rated from the 90 degree C column, they must be used at an ampacity lesser than or equal to what is listed in the 75-degree column.

Welcome to The Forum

 

[ramsy]

So the first pic is from a text that I have ..The text shows that it's "OK" to run 300 amps through 2/O wire..

The first pic was taken from Table 310.15(B)(17) (formerly Table 310.17) and should only apply to conductors in free air.

Your text book failed to identify the source of this table, and should not apply it to SC type feeders anywhere except in Free Air.

 

[Smatthew 219]

Found in NEC 2008' Table 405. (B)

Found in NEC 2008' Table 405. (B)

The first cable is Type SC, which gets such high ampacities by using High strand count wire, and insulation that is rated to 105* C. I had to look it up, apparently is used for temporary installations for things like stage lighting. As far as I can tell, it is not an NEC approved chapter 3 wire type, so it cannot be used in permanent installations.

Picture number 2 from the 2008 NEC is for approved wiring types like xhhw. Although they can be de-rated from the 90 degree C column, they must be used at an ampacity lesser than or equal to what is listed in the 75-degree column.

Welcome to The Forum

Thanks for the Reply.

I actually took a photo of one of the wires we use (for entertainment) and it was labeled with the table ref to 405B. You were right about the high-strand count and insulation rendering that particular wire being used for things like "stage lighting. That's actually what I do. Now I can finally sleep

Thanks Again,
Smatthew

 

[Smatthew 219]

Found Answer on the Wire at Work....and you were correct

Found Answer on the Wire at Work....and you were correct

The first pic was taken from Table 310.15(B)(17) (formerly Table 310.17) and should only apply to conductors in free air.

Your text book failed to identify the source of this table, and should not apply it to SC type feeders anywhere except in Free Air.[/QUOTE

HI Ramsy,

Stamped on all of the cable at work today I found the reference to NEC 400.5B and it is, indeed, allowable to run 405 amps through 4/O, 300 through 2/O, etc.
I work in the entertainment field and not in permanent installations so I was looking in the wrong part of the NEC. The book did not identify a source, like you said, which is kind of an error on the publishing co.'s part, I suppose. So the book did NOT identify the source but I found it on the cable and got some more info from another response regarding the high strand-count and insulation.

Thanks Much.
Smatthew:ashamed: