Using Voltage Drop Calculator to Determine Voltage Drop

Voltage drop is the total voltage lost to resistance forces when the electrical current is passed through a circuit. It always takes place when the voltage at the beginning of the cable is higher than the end. Regardless of size, wires will have some resistance, and passing a current through the dc resistance will result in voltage drop. The resistance and reactance of the cable increase with length. This explains why voltage drop is a significant problem with longer cable runs, for instance, in more significant buildings. The technique behind this is used when properly sizing conductors in any phase.

Electrical cables with current always have an inherent resistance to the flow of current. Excessive voltage drop in a cable can result in lights flickering or dim while motors turn hotter than usual and burn out. In such a situation, the load tends to work harder with less voltage pushing the current.

Solving Voltage Drop

To reduce the circuit’s voltage drop, there must be an increase in the cross-section of the conductors to reduce the overall resistance of the cable length. Typically, a more oversized aluminum or copper cable size increases cost; therefore, calculating VD to establish the optimum voltage is very important. It will reduce the voltage drop to safe levels without spending much.

The easiest way to fix voltage drop is by increasing the diameter of the conductor between the load and the source, which in turn lowers the resistance. Any power can be transmitted with a lower voltage drop in the power supply system if a high voltage is used.

There are four steps to reducing voltage drops:

  1.       Reducing the load power
  2.       Increasing the size of conductors
  3.       Reduces the temperature of the conductor. High temperatures will resist the flow hence causing voltage drop to rise.
  4.       Reducing the length of the conductor.

Voltage Drop Must Be Determined On Assemblies of Long Cables

In assembling long cables, it’s essential to determine voltage drop due to possible safety hazards. The reasons behind this are possible damages to cables, power loss to equipment, and safety issues.

Possible Damage to Wires and Cables

When a voltage drop occurs, it produces heat. Excess heat accumulates in the cable or wire with can damage insulation. The kind of damage caused can range from breaking down the insulation material to the unstiffening of the material, resulting in breaking the wire or cable when it’s moved or bent. This reduces the life of the wire or cable and can result in severe other safety issues. Too much heat accumulation can also damage the conductor material and cause an increase in resistance, which combines the issue, resulting in more voltage drop and heat.

Loss of Equipment

The availability of voltage and overall power significantly decreases with loss of power to equipment. When excess voltage is lost, the equipment may not work correctly or not work ultimately. For some equipment like compressor devices, or pumps, even a slight voltage loss may issue.

Security Issues of Shock and Fire

Shock and fire are the primary safety issues. If the insulator is destroyed to the extent it tears away, leaving conducting wires exposed, a user can accidentally touch the open area and get a shock. Heat builds up as voltage drop increases. Excess heat can weaken the material to the extent where arcing between conductors may occur. Prolonged accumulation of heat until a fire is produced with the insulation and nearby combustible materials such as carpet.

Controlling Information

Apart from safety issues on long cable assemblies, some guidelines and other governing information should be followed.

UL 817

This stipulates that cables are set to be derated after 50ft and 100ft to increase overheating issues due to voltage drop. Some specified cable assemblies also have restrictions on length.

NEC Rule 210.19

This needs not less than 5 percent of voltage drop at the outlet.

CSA needs more than 5 percent from the inlet to the point of use.

Requirements by Some Countries

Most countries like the UK as well have set requirements in place. So it’s always good to confirm with safety agencies if one intends to send equipment with long cables to a foreign country.

Interpower Policy

This is to determine voltage drop for requested long cable assemblies and inform the client of any possible issues when the voltage drop goes beyond 5 percent. In such cases, the client is notified about the findings, which are calculated for details regarding their application’s voltage and current usage.

Calculating Voltage Drop

There are two methods of calculating voltage drop – manual calculation and the use of a voltage drop calculator.

Voltage Drop Calculator

A more straightforward way is to search for “voltage drop calculator” online. Provide the requested details, and it will automatically calculate the percentage voltage drop together with the remaining voltage. But a lot of caution should be observed since many of these are configured for North American cable; for global measurements, use the nearest matching AWG size. This can be determined by looking at UL 62 or contacting the cable producer for help. offers the best example of this calculator since it also gives a cable chart on the same page that a user can easily find.

Manual Calculation

To calculate the voltage drop, one must first get the possible direct current resistance from a related standard or use the length of cable to measure the resistance. This method is not that accurate and will not give the correct voltage drop numbers but will be near enough to identify possible units.

After getting the size ohms/ft of a cable, the value must be multiplied by the assembly length in feet. This provides the overall possible resistance for that assembly. It’s just about applying Ohm’s Law by multiplying the assembly resistance value by the strong state current to achieve the voltage drop. This value can then be used with the primary voltage value to calculate the remaining voltage and percentage loss.

Voltage is just a potential variation. Since the current moves from high to low-end areas, it is therefore negative.

Comments are closed.