Mike Holt's "Conductor Sizing and Protection" Error in the text?

Status
Not open for further replies.
J

jsanchezuf

New member
On pg 152 of "Mike Holts guide to Conductor Sizing and Protection: calculations 2008 edition", there seems to be an error: under author's comment, it states that an "8 THHN insulated conductor has a 90 degree celcius ampacity of 50 A in dry location", yet I can't see that on Table 310.16, on page 151. Is this an error? I'm confused.

Thanks
 
barbeer

barbeer

Senior Member
Location
Pinellas County, FL
I do not have the publication but...........
310.8 tells you what insulation type goes where, thhn is under (B) dry and damp and table 310.13 and 310.16 should give you the rest of the story.
 
Dennis Alwon

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
jsanchezuf said:
On pg 152 of "Mike Holts guide to Conductor Sizing and Protection: calculations 2008 edition", there seems to be an error: under author's comment, it states that an "8 THHN insulated conductor has a 90 degree celcius ampacity of 50 A in dry location", yet I can't see that on Table 310.16, on page 151. Is this an error? I'm confused.

Thanks
Click to expand...

Not sure of the problem but you cannot terminate at 90C unless the terminals are rated 90C. I have never seen a 90 C termination but I do know almost all breakers are 75C. Maybe this is why you must use the 50 amps. You may use 55 amps for derating.
 
M

mike@mikeholt.com

Moderator
I don't have a book titled "Mike Holts guide to Conductor Sizing and Protection: calculations 2008 edition". But the ampacity of 8 THHN is 55A as per Table 310.16. However this has nothing to do with conductor sizing for terminals 110.14(C).

Conductors are 'sized' to terminal temperature rating, but conductor 'ampacity' is based on Table 310.16 based on conductor insulation temperature rating. Conductor ampacity is adjusted based on 'conductor ampacity.'

To fully understand this issue, see Example D3(a) Industrial Feeders in a Common Raceway in the 2008 NEC.
Extracted Text: A 90?C 2/0 AWG conductor has a Table 310.16 ampacity of 195 amperes. Adjusting for the conditions of use (35?C ambient temperature, 8 current-carrying conductors in the common raceway),
195 amperes ? 0.96 ? 0.7 = 131 A
 
zappy

zappy

Senior Member
Location
CA.
wow i never seen mike holt respond before!

wow i never seen mike holt respond before!

Awsome!I wish he would respond more!
 
J

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
electricalperson said:
heres a 90 degree c lug http://ebusiness.ilsco.com/webapp/wcs/stores/servlet/CategoryDisplay?storeId=10001&langId=-1&catalogId=1&categoryId=192
i dont know about lugs on breakers, so the ampacity has to still be adjusted for 75 degrees if im not mistaken. if its not marked with tempature then its 60 degree
Click to expand...

110.14(C) deals with the termination not the lug. There are no UL listed molded case circuit breakers or disconnect switches rated for wire sized above 75?C.
 
Smart $

Smart $

Esteemed Member
Location
Ohio
jim dungar said:
110.14(C) deals with the termination not the lug. There are no UL listed molded case circuit breakers or disconnect switches rated for wire sized above 75?C.
Click to expand...
Yes... but everyone seems to be so quick to point out 110.14(C)(1) that they completely forget about 110.14(C)(2) and the FPN.

For example, busbar "jumpers" may qualify as 90?C terminations under 110.14(C)(2) when using say THHN and 90?C-rated compression lugs.
 
Status
Not open for further replies.
Top