Example 1 from NEC Handbook Section 220.40
Given:
Feeder Circuit with following parameters.
3 phase 4 wire feeder full size
Neutral 125 ampere noncontinuous load 200 ampere continuous load 75
Degree C terminal temperature rating Type THHN insulated conductors (THWN
was given in the original problem, but was changed to THHN in the solution)
Four current carrying copper conductors in a raceway Majority of load is
nonlinear Solution : 600 kcmil conductors
protected by a 400 ampere overcurrent protective device (OCPD)
Example 2 from NEC Handbook Section 210.20(A)
Given:
Branch Circuit with following parameters.
25 ampere continuous load 60
Degree C terminal temperature rating Type THWN insulated conductors
Four current carrying copper conductors in a raceway Majority of load is
nonlinear Solution: No. 8 AWG conductors
protected by a 35 ampere overcurrent protective device (OCPD)
Example 3 from Mike Holt online examples
Given:
Branch Circuit with following parameters.
53 ampere continuous load 75
Degree C terminal temperature rating Type THHN insulated conductors
Four current carrying copper conductors in a raceway Majority of load is
nonlinear Solution : No. 4 AWG conductors
protected by a 70 ampere overcurrent protective device (OCPD)
Example 4 from Mike Holt online Examples
Given:
Feeder Circuit with following parameters.
3 phase 4 wire feeder full size
Neutral 184 ampere continuous load 75
Degree C terminal temperature rating Type THHN insulated conductors
Four current carrying copper conductors in a raceway Solution: 250 kcmil conductors
protected by a 250 ampere overcurrent protective device (OCPD)
Example 5 from McGrawHill's NEC
Handbook
Given:
Branch Circuit with following parameters.
100 ampere continuous load 75
Degree C terminal temperature rating Type THHN and THW insulated conductors
Four current carrying copper conductors in a raceway Majority of load is
nonlinear Solution :
No. 1 AWG THHN or No. 1/0 AWG THW conductors
protected by a 125 ampere overcurrent protective device (OCPD)
Example 6 Nonmetallic Cable
Given:
Branch Circuit with following parameters.
16 ampere continuous load Four each 2conductor w/ground NM cables in a 36 inch long raceway used for firestopping.
Conductors are copper Analysis:
Per Section 334.80
The ampacity of Types NM, NMC, and NMS
cable shall be determined in accordance with 310.15.
The ampacity shall be in
accordance with the 60°C conductor temperature rating. The 90°C
rating shall be permitted to be used for ampacity derating purposes,
provided the final derated ampacity does not exceed that for a 60°C rated
conductor. To apply these
rules select the conductor as "NM Cable  90 C" and the terminal temperature
as "NM  60 C." There are 8 current carrying conductors.
Solution : No.
12 conductors
protected by a 20 ampere overcurrent protective device (OCPD)
