# what exactly does potential drop mean and how does it help or work in order to find the current in a circuit??? please say it with a circuit diagram

Nirmal Singh.
10 years ago

light has particles of photons.The big difference between electric and magnetic fields is that (as far as we know) there are no isolated magnetic charges. If there were isolated magnetic charges e.g. if you could watch a magnetic monopole as a light wave passed by then you'd see similar behavior to an electron. But there aren't, therefore light does not affected by magnetic fields

Thanks & Regards,
Nirmal Singh

Nirmal Singh.
10 years ago

Wires carrying current always have inherent resistance, or impedance, to current flow. Voltage drop is defined as the amount of voltage loss that occurs through all or part of a circuit due to impedance.

A common analogy used to explain voltage, current and voltage drop is a garden hose. Voltage is analogous to the water pressure supplied to the hose. Current is analogous to the water flowing through the hose. And the inherent resistance of the hose is determined by the type and size of the hose - just like the type and size of an electrical wire determines its resistance.

Excessive voltage drop in a circuit can cause lights to flicker or burn dimly, heaters to heat poorly, and motors to run hotter than normal and burn out. This condition causes the load to work harder with less voltage pushing the current.

The National Electrical Code recommends limiting the voltage drop from the breaker box to the farthest outlet for power, heating, or lighting to 3 percent of the circuit voltage. This is done by selecting the right size of wire and is covered in more detail under "Voltage Drop Tables."

If the circuit voltage is 115 volts, then 3 percent of 115 volts is 3.5 volts. This means that voltage lost from the wires in the circuit should not exceed 3.5 volts and the outlet should still have 115 - 3.5 or 111.5 volts to supply. Since most appliances require an extension cord to plug into an outlet, some voltage drop will occur in the extension cord as well. Some motors will not run correctly, and could even burn up, if the voltage at the motor falls too low.

## How to calculate voltage drop

Single-phase voltage drop calculation:

Three-phase voltage drop calculation:

OR 3øVD = (SQRT(3)*L*R*I)/1000

VD = Voltage drop (conductor temp of 75°C) in volts

VD% = Percentage of voltage drop (VD ÷ source voltage x 100). It is this value that is commonly called "voltage drop" and is cited in the NEC 215.2(A)(4) and throughout the NEC.

L = One-way length of the circuit's feeder (in feet)

R = Resistance factor in ohm/kft

I = Load current (in amperes)

Source voltage = The voltage of the branch circuit at the source of power. Typically the source voltage is either 120, 208, 240, 277, or 480 V.