Ampacity question


  #1  
Old 08-12-08, 10:52 AM
S
Member
Thread Starter
Join Date: Dec 2006
Location: orange county
Posts: 268
Upvotes: 0
Received 0 Upvotes on 0 Posts
Question Ampacity question

Can 2 current carrying conductors ( 12awg with ground ,thwn ,120v, from 20 amp c/b ) be run in the same raceway (emt) with two current carrying conductors (240 v, 8awg thwn from 40 amp c/b?) The distance is approximately 50 feet. Thanks
 
  #2  
Old 08-12-08, 11:00 AM
I
Member
Join Date: Jul 2008
Posts: 68
Upvotes: 0
Received 0 Upvotes on 0 Posts
Im no electrician but Im going to take a stab at this one. I think the max conductors before you have to derate is 3, so, you have to derate by 80% if you want to put all 4 together. I would say that you may have to limit the new circuit to no more than 15 amp but hey, I could be wrong. I stand corrected if I give out erroneous info!
 
  #3  
Old 08-12-08, 11:23 AM
M
Banned. Rule And/Or Policy Violation
Join Date: Dec 2007
Location: Chicago
Posts: 904
Upvotes: 0
Received 0 Upvotes on 0 Posts
Cerrowire conduit fill calculator: Conduit fill calculator
 
  #4  
Old 08-12-08, 11:25 AM
I
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 9,785
Upvotes: 0
Received 45 Upvotes on 43 Posts
That is okay. For 4-6 conductors the derating factor is 80% (table 310.15b2a), so we'll have to derate both the #12 and the #8. Derating always starts from the 90°C column of table 310.16, so the initial ampacities of #12 and #8 are 30A and 55A respectively. Apply the 80% factor to each and you're left with 24A and 44A which are greater than the values of the breakers so you're okay.
 
  #5  
Old 08-12-08, 08:09 PM
S
Member
Thread Starter
Join Date: Dec 2006
Location: orange county
Posts: 268
Upvotes: 0
Received 0 Upvotes on 0 Posts
Smile

Thanx fellas for your time. Thanx ibpooks for the detailed response. I have to learn how to do this myself. I love to study but hate charts (lol). It all began with the psychometric and mollier charts in A/C school 32 years ago, ugh.
 
  #6  
Old 08-12-08, 08:46 PM
F
Member
Join Date: Mar 2006
Location: NE Wis / Paris France{ In France for now }
Posts: 4,364
Upvotes: 0
Received 2 Upvotes on 2 Posts
Sidecutter that set up will work fine without issue but it depending on what size conduit you are using any chance you are useing the ½ inch it may be ok depending on the type of conductor itself.

otherwise ¾ inch will work better this way.

and yeah Ibpooks did expain very clear on the derating there.

Merci,Marc
 
  #7  
Old 08-13-08, 01:56 AM
S
Member
Join Date: Jul 2008
Posts: 45
Upvotes: 0
Received 0 Upvotes on 0 Posts
I agree with everyone's responses and am impressed by ibpooks detailed and clear response. My old boss would read those tables concerning what can fit in a pipe. Sure, the tablesays so.If there is any question at all, don't hesitate to increase the size of pipe. You will be much happier if you use common sense and not rely on the table. I have personally paid the price for that table to save money for the company. Not worth the grief
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: