Preparing to pass your electrical exam means preparing to use the wire size equation calculations to answer exam questions. Can you answer the following question with ease?
Question:
What size THW conductor is required to supply a 30 amp load 180 ft. from its’ single-phase 120 v load?
A. #10 gauge
B. #8 gauge
C. #6 gauge
D. #4 gauge
Solution:
D. #4 gauge
Step #1
Use the wire size equation for single phase circuits:
CM = 2 x K x D x I/VD Permitted = 2 x 12.9 x 180 ft. x 30 amps/3.6 volts = 38,700 area circular mils
Table 8 of Chapter 9 indicates that #4 gauge at 41,740 circular mils in the minimum area circular mil size required. Table 310-16 indicates that a #4 THW copper conductor will accommodate up to 85 amps.
Our patient and knowledgeable instructors will help you to understand how to determine the voltage drop permitted as well as the approximate resistance per circular mil foot of conductor in ohms, both of which are required when using this formula.
Careful exam preparation is the key to achieving a passing score on your electrical exam. Click the “Register Now” tab or call 888-919-3926 to start preparing to pass your exam today.