# DC Voltage drop calculator

This online calculator can be used to estimate the voltage drop (volts), voltage drop (%) and the final voltage after the voltage drop for DC circuits.

Formula for calculating voltage drop

This voltage drop calculator is based on the formula, **voltage drop = I * R** where:

- I is the DC current flowing in the circuit
- R is the direct current resistance for the wire.

This calculator uses DC resistance from NEC 2017, Table 8 and assumes conductor temperature of 75°C (167°F), uncoated single and 7 strand copper and aluminum wire.

**Note:** The results of this calculator should only serve as a guide. We shall therefore not

accept any liability resulting from the use of this calculator. Always consult the manufacturer specification’s or a competent professional if unsure.

## How to minimize voltage drops in AC and DC applications

Voltage drops result in power wastage along the cable or wire and a reduced voltage which

may cause the appliance not to work properly.

**Causes of voltage drops**

**1.Longer cable runs increase voltage drops**

For example, at 13.8V, an appliance drawing 5A over *one-way length of 10 feet* of 14 AWG wire results in a voltage drop of 2.25%.

Should this distance double (20 feet), then the voltage drop would nearly double to 4.57% increasing the power wastage and may result in the appliance not working properly.

**Fix:** To maintain the voltage drop (2%) while maintaining the cable length, increase the wire gauge. In this case, using 10AWG would keep the voltage drop to 1.81%.

**2.Wrongly sized wire gauges for large appliances increase voltage drops**

Larger appliances (larger loads) require more current which results in a bigger voltage drop for the same distance.

To reduce the voltage drop, you need to increase the size of wire (use a lower gauge number).

*For example:*

For example, at 13.8V, an appliance drawing 5A over 10 feet return of 14 AWG wire results in a voltage drop of 2.25%.

Should a larger appliance that draws twice the current (10 A), then the voltage drop would nearly double to 4.57% increasing the power wastage and may result in the appliance not working properly.

**Fix:**

*1. If this is not possible to move the load (reduce the cable length, you may use a large diameter cable, such as 12AWG). This reduces the voltage drop to 2.9V.*

*2. Increase the supply voltage to 24V if the load can take it which reduces the voltage drop to 2.6%.*

**In summary**, you can minimize voltage drops by selecting a suitable wire gauge and length for a given appliance (load) such that the voltage at the end of the circuit satisfies the appliance’s requirements.

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