Voltage Drop Calculator – Check Voltage

A useful tool to help give us a rough estimate of Voltage drop that may occur in our Elctrical Wires / Conductors. Voltage drop occurs due to the level of Resistance present within an Electrical conductor.

Understanding how a Voltage drop works can help us in designing our Electrical Schematic, sized Electical Wires, to understand electrical drops (as they can cause ineffeciencys machinery, lumens falling, Motors overheating and electirc devices not working properly).

Voltage drop is often used for residential, commercial and industrial electircal installs in the USA. As an electrician / electrical engineer we can use the volts drop calculations to help us understand what wire sizes (Based on their AWG) to choose.

For example if we have a long electrical circuit using low copper wire and a current of 20amps we are likely to get a higher voltage drop than a short circuit with a larger conductor.

The Voltage Drop calculator can help give us 3 key things; Voltage Drop, Voltage Available and Percentage Voltage Drop. It can help when planning maybe the wiring for electrical devices.

Whether you are working on a residential project, outdoor lighting, HVAC or commerical eletrical install we can make better decisions on how big the wire should be.

How to Use

Using the Voltage Drop Calculator is very easy,Whilst entering our electrical details we can get our estimate.

1. Supply Voltage - What is the Voltage permanent in your circuit? 120V / 208V / 240V / 480V

2. Current - What is the current of your Electrical Circuit AMS?

3. Wire Material - What type of wire are you using? Copper or ALuminium?

4. Wire Size - Choose you conductor wire size. Select from the options below for AWG or Metric sizes.

5. Circuit Length - What is the one way length from the Source?

6. Circuit Type - What type of electrical circuit are you using? Single Phase DC, Single Phase AC or 3 Phase AC

7. Press the Calculate Button

8. Your Voltage Drop Results Will Appear Below!

Make sure to double check your units and layout matches above.

Voltage Drop Formulas

Depending on what Circuit you are using, whether it be DC, 1 Phase AC or 3 Phase AC the voltage drop formulas will be used.

1. DC Formula

Voltage Drop = (2 x I x L x R)/1000

2. Single Phase AC Formula

Voltage Drop = (2 I L Rcosφ + Xsinφ)/1000

3. 3 Phase AC Formula

Voltage Drop = (SQRT(3) I L Rcosφ + Xsinφ)/1000

Where:

Vd – Voltage Drop Voltage (V)

I – Current (A)

L – Conductivity Length (Feet)

R – Conductivity Resistance (Ώ per 1,000ft)

X – Conductivity Resistance (Ώ per 1,000ft)

– Power Factor

– Sin of power factor Angle

Although there is no conductivity reactance for DC and those without complex calculations, in AC there could be variations due to Impedence and Power Factor.

Voltage drop Percentage formula

Voltage Drop (%) = (Vd / Vs ) x 100

Where

Vd – Voltage Drop Calculated

Vs – Voltage supplied

Load Voltage

Voltage Load = Vs – Vd

Giving us an understanding of how much voltage is lost between our power supply and where its being used.

Example

Let’s say we have a 120v DC Circuit in our residence / workshop, Using a copper electiral conductor, With 20 Amps and a 50 Foot (one way).

With a conductivity resistance of 1.588 Ohms Per 1,000ft (Approx 20°C 12 AWG Copper).

We have the following information;

Measurement Value

Supply Voltage 120V

Current 20A

Wire Material Copper

Wire Size 12AWG

Length 50 foot

Resistance 1.588 Ω / 1,000ft

1. Voltage Drop (DC Formula)

Voltage Drop = (2 x I x L x R)/1000

2. Input Values

Voltage Drop = (2 x 20 x 50 x 1.588)/1000

3. Calculating Voltage Drop

Voltage Drop = 3.176V

4. Calculating Voltage Drop (%)

= (3.176 / 120) x 100

= 2.65%

5. Calculating Load Voltage

Voltage Load = 120 – 3.176

= 116.824V

Results

The Voltage drop is estimated to be 3.176V therefore meaning Around 2.65% of the supplied voltage is lost. The voltage available at the load is estimated to be 116.824V.

This is due to the basic calcuation for DC using Resistance Only. In real situations the conductivity resistance will differ dependant on the temprature its opperating at.

Understanding Voltage Drop Results

After inputting your electircal details several of the following results will appear;

Voltage Drop – This calculates how much Voltage is decreased across the conductor. A higher value indicates a higher volts drop.

• Voltage Drop (%) – This gives a figure of Voltage drop as a percentage, helping to identify how well your circuits are going depending on their Voltage Supplied.
• Voltage At Load – Indicates the Voltage estimated available at the device.
• Conductivity Resitance – Shows how much this conductor will resist the electrical current. A lower resistance overall will mean less Voltage drop.
• Length – Indicates how far the electricity has to travel in the conductor. 2 Wires are used normally in DC / Single Phase Circuits.

Less Voltage Drop indicate a more efficient power delivery. However this will depend how much is acceptable on your installation, devices etc. and covered in Electircal Codes.

Voltage Drop Factors

Several factors will affect voltage drop.

1. Conductor Size

LARGER Conductors = Less Electrical Resistance. 10 AWG copper will generally have less resistance than 12 AWG Copper Conductor.

2. Conductor Material

Different materials have varying resistances. Copper will generally have less resistance than aluminium.

3. Length

Longer wires create more resistance. This can affect things like Outdoor Lighting Garages and Long distances.

4. Current

The larger the current more volts drop there will be. 30 amps will create more volts drop than 15Ammps through the same conductor.

5. Voltage Supplied

The Volts drop will be based on the Conductor and Current however for percentage to relate, the supplied voltage affects this. A Voltage loss of 3.176 volts would be a larger percentage loss from 120volts compared to 240 Volts.

6. Temprature

More resistance the higher the conductivity gets. This can create a larger volts drop.

7. Power Factor & Reactance

Within AC circuits Power Factor and Conductivity Reactance can impact. This can be useful on longer circuits and when installing Motors etc.

Benefits of Using

1. Electircal wire Sizing

Electricians can use to compare wire sizes (AWG). Giving an indication of what conductor will give us an acceptable voltage drop.

2. Domestic

Helpful for giving us an idea of Voltage drop to occur in Lighting, Outlets Appliances etc.

3. Commertial

Can help give us an understanding of what voltage drop will occur over longer distances in Offices, Warehouses, Retail Buildings etc.

4. Solar Panel System

Help to get an indication of Voltage drop in DC circuit between Panels, Charge Controllers, Battery and Inverters.

5. HVAC – Air Conditioners etc.

Help to understand any Voltage Drops in circuits with Air Conditioners, Heat Pumps, Compresser.

7. Helping efficiency

By knowing if there is a high voltage drop we can minimise wastage.

8. cuts down on time

Save electricians having to do calculations over and over again by allowing multiple comparisons to be made quickly.

Accuracy

The voltage drop calculator will give us estimates based on the information provided.

• Actual Voltage Drop may be different as,
• The length and wire size are assumed to be correct.
• The resistance can change depending on the operating temprature.
• Basic calculations don’t include Reactance or Power Factor.
• More calculations may need to be done for AC.
• Additional resistance may happen at joints, terminals, splices etc.

Actual Voltage drop can vary. The calculations below are based on the installation. Aliminium or Copper will have different required resistances. This calulator shouldn’t be used for calculating Load / Conductor Ampacities / Overcurrent Protection or for complience with code. If you are fitting an electrical installation in the USA please refer to the relevant National Electrical Code (NEC), any local Amendments / Equipment Specs and use a Qualified Electician. Often referenced as the NEC recommends around 3% voltage drop for branch circuits and 5% total for feeders branch circuits. How ever this is seen as information only and is recommended in many cases.

Never choose wire for Voltage drop only factors, Consider Amperage, temperature Rating of insulation, installation factors and other requirements.

FAQ

What is voltage drop.

Voltage Drop refers to the reduction in Electircal Voltage during current flow. It occurs due to the resitance present in the wires. Longer wires (small conductors, high current) will have a higher voltage drop.

How to calculate voltage drop.

Use the formual Vd = (2 × I × L × R) ÷ 1000. For a simplistic DC circuit. Where I is current measured in AMP’s, L is one way length in feet and R is conductor resistance (ohm’s).

What is an acceptable voltage drop in USA.

Often referenced as 3% max voltage drop for Branch circuits and 5% total (Feeders & Branch) in NEC. However this will vary on installation, what code covers it and equipment specs.

Is voltage drop affected by conductor size?

Yes Larger size wiring will have less electrical resistance and therefore less volts drop. 10AWG copper will have less volts drop than 14 AWG copper, when supplied with the same current and distance.

Is voltage drop different for copper vs Aluminium wiring?

Yes Copper will generally have less resitance when compared to Aluminium with the same sizing. Aluminum Conductors will need a Larger CSA to have similar electircal quality.

Is voltage drop affected by conductor length?

Yes increase length will increase Voltage Drop. More elctricity resitance will occur in longer circuits. With most 2 wire DC / Single phase circuits you need to allow for both ways.

Can I use Voltage drop calculator for 3 phase?

Yes you can use a Voltage drop calculator for 3 phase. Just make sure it uses the 3 Phase calulation. Line to line voltage, conducotrs resitance, reatance, current, length and power factors where applicable.