Conductor Derating Question

[Eurbin Electric]

When installing more than 3 current carrying THHN conductors in a conduit they must be de-rated. Can you use the ampacity from the 90 degree column of table 310.16 as a starting point for the calculation if the breaker you are landing on has a termination value of only 75 degrees?

 

[A/A Fuel GTX]

Yes, but look at 310.15(B) for the clarification. The table you are looking for is 310.15(B)(16).

 

[Bang]

When installing more than 3 current carrying THHN conductors in a conduit they must be de-rated. Can you use the ampacity from the 90 degree column of table 310.16 as a starting point for the calculation if the breaker you are landing on has a termination value of only 75 degrees?

Just out of curiosity, why would you want to use insulation rated @ 90 degrees as opposed to 75 degrees IF the reason is other than shortage of material on hand?

 

[jumper]

Just out of curiosity, why would you want to use insulation rated @ 90 degrees as opposed to 75 degrees IF the reason is other than shortage of material on hand?

For derating and correction factors.

Ever hear of a 20A 3P "full boat"?

 

[sameguy]

THHN

 

[Bang]

No, I haven't heard of it....Enlighten me.


Looking at the question now I understand.....I was tied up around the breaker termination being rated for 75 degrees.....

 

[charlie b]

The phrase "full boat" is a common "trade slang," and is specifically intended to apply to a multi-wire branch. It refers to a set of five wires: Phases A, B, and C, the neutral, and the equipment ground (although if you use the conduit to serve as an EGC, you don't need the fifth wire). If you look at all the relevant NEC articles (I think that three come into play here), you will see that you can put three "full boats" into the same conduit, if you use THHN or another conductor type that is rated for 90C, and still use #12 wire and 20 amp 3-pole circuit breakers. If you try to put four full boats into the same conduit, and want to use 20 amp breakers, you need to upsize to at least #10 wire.

 

[resistance]

Must be common in commercial industrial. Because I?ve never heard the term: ?Full Boat"

 

[jumper]

Must be common in commercial industrial. Because I?ve never heard the term: ?Full Boat"

Yes, it is a commercial/industrial term. Not used in residential.

 

[John120/240]

Yes, it is a commercial/industrial term. Not used in residential.

Full Boat, Full House, Round House... I'm sure there are other acroymons for a full boat

 

[Bang]

Thanks for enlightening me!!!! I'm taking everything coming my way!!!

 

[Smart $]

Full Boat, Full House, Round House... I'm sure there are other acroymons for a full boat

Hmm... not acronyms... just slang [trade] terminology.

One electrician I used to work with used the terms "edisons". A three-wire or partial edison would be two hots and a neutral (usually w/grd) on a wye system.

 

[Smart $]

... The table you are looking for is 310.15(B)(16).

Only in the 2011 edition. Previously Table 310.16.

 

[charlie b]

I have also heard this called a "network." I don't remember the context.