|
How to determine the length of a cable using a ohmmeter
Short-circuit one end of the phone wire pair and measure the resistance between the two wires at the other end.
Multiply the resistance by 20 to find the length of the wire in feet. For example, a reading of 54.6 ´ 20 » 1,100). For a maximum of 1,500 ft., the resistance must measure 75 ohms or less. This formula works for standard 24-gauge phone wire.
Cable Lengths and Gauge DC Resistance Chart
18 Gauge
| 78 X ohms = resistance |
51 |
32 |
25 |
12 |
6 |
4 |
2 |
| feet |
4,000 |
2,500 |
2,000 |
1,000 |
500 |
300 |
200 |
20 Gauge
| 50 X ohms = resistance |
80 |
50 |
40 |
20 |
10 |
6 |
4 |
| feet |
4,000 |
2,500 |
2,000 |
1,000 |
500 |
300 |
200 |
22 Gauge
| 31 X ohms = resistance |
129 |
80 |
64 |
32 |
16 |
9 |
6 |
| feet |
4,000 |
2,500 |
2,000 |
1,000 |
500 |
300 |
200 |
24 Gauge
| 20 X ohms = resistance |
200 |
125 |
100 |
50 |
25 |
15 |
10 |
| feet |
4,000 |
2,500 |
2,000 |
1,000 |
500 |
300 |
200 |
26 Gauge
| 12 X ohms = resistance |
133 |
208 |
166 |
83 |
41 |
25 |
16 |
| feet |
4,000 |
2,500 |
2,000 |
1,000 |
500 |
300 |
200 |
Note: 27 Gauge and above is not recommended.
|
