# 12 Volt Current and Maximum Wire Length

## Maximum copper wire length with 2% voltage drop

### 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

* Voltage (volts)*

* Current (amps)*

* Cross sectional area (mm ^{2}) - AWG Wire Gauge vs. mm^{2} *

* Voltage Drop (%)*

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*