In reality, calculating the maximum length can be tedious if you are not an electrician or an engineer. The actual calculation involves adjusting power factors of impedance values and accounting for temperature’s effect on resistance before voltage drop could be computed. Although this method is quick and conservative, several factors have been eliminated to get the true length. This estimate using this method is quite close to our value of 85 feet (within ±5%). This can help you estimate the length of wire on a 20 amp breaker within the 5% recommended voltage drop. You can also try using this equation if you want to know how long you can run 10 gauge wire from the combined feeder and branch circuit. Length(feet)=voltage drop (volts)∙1000 feet/2∙current amps∙impedance (ohms)=3.6 volts∙1000 feet/2∙20 amps∙1.1 ohms=82 feet The impedance of 10 gauge wire at 0.85 power factor would be 1.1 ohms per 1000 sq. Then we get impedance from Chapter 9, Table 9 from the NEC. We first get the actual voltage drop from a 120 volt source if we are limit the voltage drop to 3%: Let us try to estimate how long we can run 10 gauge wire on a 20 amp circuit at 120 volts using this method. Voltage drop (volts)=voltage drop %∙source voltage (volts)100% Length(feet)=voltage drop (volts)∙1000 feet/2∙current(amps)∙impedance (ohms) Voltage drop (volts)=2∙impedance(ohms)/1000 feet ∙current amps∙length (feet) The wire length in this assumption can be derived from voltage drop: These online websites can allow you to configure your results based on your specific requirements.įor example, if you need the length of 10 gauge wire for 220V circuits, an online calculator can easily provide you with a result.Ī crude estimate some people do is to assume the behavior of single phase AC as DC and use the available data in the US National Electric Code Chapter 9 Table 9 for impedance instead of resistance. Calculation of the Distance Limit of 10 Gauge WireĪ convenient way to approximate the maximum length is to use an online calculator. Take note that this will not be true for thicker wire gauges. This means that the maximum length you can run 10/2 wire or 10/3 wire for 30 amps at 120 volts may still be around 57 feet, and at 240 volts will be 114 feet. Maximum Length for Types of 10 Gauge Cablesġ0 gauge multiconductor cables will have approximately the same maximum running length as a single conductor. It also shows the length for 30 amps (the maximum amp rating for 10 gauge copper wire).ġ0 gauge copper wire can carry 30 amps up to 57 feet for 120 volts, and up to 114 feet for 240 volts. The table shows the wire length for 15 amp and 20 amp household circuits.
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