Written by Harvey Ursaki, February 26, 2020
Voltage drop is defined
as the amount of voltage loss that occurs through all or part of a circuit due to
impedance. Understanding voltage drop is the key to a successful circuit
A common analogy used
to explain voltage, current and voltage drop is a garden hose. Voltage is like
the water pressure supplied to the hose. Current is like 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.
Voltage drop (VD)
occurs when the voltage at the end of a run of cable is lower than at the
beginning. Any length or size of wires will have some resistance and running a
current through this resistance will cause the voltage to drop.
As the length of the
cable increases, so does its resistance increase in proportion. Hence, VD is
particularly a problem with long cables runs, for example in larger buildings
or on larger properties such as oil/gas plants.
carrying current always present inherent resistance, or impedance, to the
flow of current. VD is measured as the amount of voltage loss which occurs
through all or part of a circuit due to what is called cable
“impedance” in volts.
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.
Most Electrical Codes
recommend limiting the voltage drop from the breaker box to the farthest outlet
for power, heating, or lighting to 3 percent of the circuit voltage.
You can calculate the
voltage drop by using any of several accepted voltage drop formulas.
Subtract the resulting number from the measured voltage decrease, and you have
Calculations are done by selecting the right size of wire using “Voltage Drop Tables” supplied by various cable manufactures or by computer programs designed for calculating the voltage drop automatically, some can even size the cable for you as well, programs like Electrical Design Management.
The longer your runs
get, the lower the voltage is at the point of utilization. But not all the
voltage difference may be due to voltage drop.
Voltage drop is not
caused by poor connections, bad contacts, insulation problems, or damaged
conductors; those are causes of voltage loss.
It’s important to
distinguish voltage drop from voltage loss. You can have both voltage drop and
voltage loss in any circuit.
Understanding voltage drop and the effects it has on an electrical circuit will help in the correct cable selection for your electrical equipment.
Harvey Ursaki, February 26, 2020
Voltage drop is defined as the amount of voltage loss that occurs through all or part of a circuit due to impedance. Understanding voltage drop is the key to a successful circuit design. A common analogy used to explain voltage, current and voltage drop is a garden hose. Voltage is like the water pressure supplied […]
Harvey Ursaki, February 14, 2020
Contrary to popular opinion, bigger isn’t always better—especially when it comes to electric motors. Plant maintenance and engineering departments like having a little extra power available “just in case,” so they sometimes specify larger motors than applications require. But oversized motors cost more to operate—sometimes a lot more. Fortunately, there’s a simple procedure for determining […]
Harvey Ursaki, January 28, 2020
While some may claim that direct-current (DC) motors are no longer relevant, that is definitely not the case. DC motors and DC converters/drives are alive and well in industry, driven by many applications in which they are the best option. Alternating-current (AC) motors have certainly decreased DC motor sales, and they do have advantages in […]
Mr. Harvey Ursaki is the Director of Programming and Operations for Electrical Design Management Software Ltd. He has over 37 years experience in the electrical industry.
Experienced in thermal and hydro generation, radial distribution substations, multi-breaker, ring bus transmission terminals. Along with many years in the oil and gas industry, he has a well-rounded knowledge of the electrical consulting industry.
Prior to forming EDM, Mr. Ursaki was Director of CLA Utility Services Ltd. an electrical consulting service, specializing in developing electrical engineering standards, serving clients in Canada, USA and in the Caribbean.
He also served as a Supervisor of Transmission Engineering for a privately- owned utility in southern British Columbia, Canada.
He now brings his years of experience to EDM company, developing an electronic standards toolbox for Engineers, Technologists and Electricians worldwide.