What is the loop resistance for a 1,000 ft run using 18 AWG copper with unit resistance 7.77 Ω per 1,000 ft?

What is the loop resistance for a 1,000 ft run using 18 AWG copper with unit resistance 7.77 Ω per 1,000 ft?

• A. 7.77 Ω
• B. 15.54 Ω
• C. 23.31 Ω
• D. 31.08 Ω

Answer: (B)

Loop resistance accounts for both directions of current in a circuit. The unit resistance given is for one conductor over 1,000 ft. For a loop, the current travels to the load and back, so the total length is doubled to 2,000 ft. Compute the loop resistance: 7.77 Ω × (2,000 ft / 1,000 ft) = 7.77 Ω × 2 = 15.54 Ω. So the loop resistance is 15.54 Ω. The other numbers would correspond to either a 1,000 ft single conductor (7.77 Ω) or longer loop lengths (about 3,000 ft or 4,000 ft total loop length).

Loop resistance accounts for both directions of current in a circuit. The unit resistance given is for one conductor over 1,000 ft. For a loop, the current travels to the load and back, so the total length is doubled to 2,000 ft.

Compute the loop resistance: 7.77 Ω × (2,000 ft / 1,000 ft) = 7.77 Ω × 2 = 15.54 Ω.

So the loop resistance is 15.54 Ω. The other numbers would correspond to either a 1,000 ft single conductor (7.77 Ω) or longer loop lengths (about 3,000 ft or 4,000 ft total loop length).