# 12 Volt - Maximum Wire Length vs. Current

### Maximum Wire Length Calculator

The calculator can be used to calculate maximum length of copper wires. Note that

- for a typical electrical circuit with two wires - one back and one forth - this is the length of the two wires together. The maximum distance between the source and the equipment is
**half**the calculated distance - in a car where equipment can be grounded to the chassis - the body of the car acts as the negative wire. The electrical resistance in the chassis can normally be neglected and the maximum distance
**equals**the calculated distance

Maximum lengths for copper conductors from power source to loads in * 12 volt * systems with * 2% * voltage drop are indicated below:

### Wire Length - feet

Download and print 12 Volt Electric Circuit Chart

### Wire Length - meter

Download and print 12 Volt Electric Circuit Chart

- double the distance if 4% loss is acceptable
- multiply distance by 2 for 24 volts
- multiply distance by 4 for 48 volts

### Example - Maximum Length of Wire

The current to a light bulb with power * 50 W * can be calculated with Ohm's law

* I = P / U (1) *

* where *

* I = current (amps) *

* P = power (watts) *

* U = voltage (volts) *

* (1) * with values

* I = (50 W) / (12 V) *

* = 4.2 A *

From the diagram above the maximum length of the total wire back and forth should not exceed approximately * 8 m * for gauge * #10 (5.26 mm ^{2}) * . By increasing the size of the wire to gauge

*#2 (33.6 mm*the maximum length is limited to approximately

^{2})*32 m*.

### Example - Calculate Maximum Wire Length

The electrical resistance in a copper conductor with cross sectional area * 6 mm ^{2}* is

*2.9 10*. This is close to wire gauge 9.

^{ -3 }ohm/mIn a * 12V * system with maximum * 2% * voltage drop - and current * 10 amps * - the maximum total length of the wire back and forth can be calculated with Ohm's law

* U = R L I (2) *

* where *

* R = electrical resistance (ohm/m) *

* L = length of wire (m) *

* (2) * rearranged for * L *

* L = U / (R I) (2b) *

* (2b) * with values

* L = (12 V) 0.02 / [( 2.9 10 ^{ -3 } ohm/m ) (10 amps)] *

* = 8.3 m *

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