⚡Question Of The Week⚡
Question:
A 24A continuous load is supplied by copper THHN conductors in EMT. The conductors terminate on equipment rated 75°C only.
The installation is in an ambient temperature of 40°C, and there are 6 current-carrying conductors in the same raceway.
The overcurrent device must be selected from standard breaker sizes only.
What is the minimum conductor size required?
Please Comment & Discuss Below.
Note: A little brain-buster for the weekend!
Disclaimer: As always with my questions, there may be errors or mistakes: feel free to call them out!
⚡ I hope you all have a great weekend! We are always learning!
⚡ Credit: TRADEHOG.NET ⚡
Table 310.15(C) (1) 5-6 conductors =80%
Table 310.15(B)(1) @ 40 degree C on 90 degrees column = 0.91( THHN insulation)
24/0.8=30/0.91=32.967
@ 75degree table 310.16 #10 good for 35A but 30A OCPD we don’t know the load type(motor, AC etc)
Franklin De los santos now remember the rules in 210.19(A)(1) and (A)(2). The question is about conductor size, the OCPD in the question is the distraction.
Lets focus on 210.19(A)(1) and 210.19(A)(2) on this question. Remember, the conductor is the larger of the results of (A)(1) vs (A)(2). Hope that tip helps.
Paul Abernathy, always appreciate the tips! Thank you!
my answer was #8 and i got it from
24A × 1.25 = 30A (NEC 210.19(A)(1)
Terminations are 75C only (NEC 110.14(C)(1)(a)
6 current-carrying conductors in the raceway 80%
(NEC 310.15(C)(1)
40C ambient, using the 75C rating 0.88
Table 310.15(B)(1)
(Table 310.16, Cu, 75C)
#8 Cu = 50A
50 × 0.80 = 40
40 × 0.88 = 35.2A
My pick: Minimum conductor size is #8 Cu THHN.
Josh A. Agreed. Others should have reviewed my tips...;)