Voltage drop
Voltage drop is the reduction in voltage
Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...

 in the passive elements (not containing sources) of an electrical circuit
Electrical network
An electrical network is an interconnection of electrical elements such as resistors, inductors, capacitors, transmission lines, voltage sources, current sources and switches. An electrical circuit is a special type of network, one that has a closed loop giving a return path for the current...

. Voltage drops across conductor
Electrical conductor
In physics and electrical engineering, a conductor is a material which contains movable electric charges. In metallic conductors such as copper or aluminum, the movable charged particles are electrons...

s, contacts, connector
Electrical connector
An electrical connector is an electro-mechanical device for joining electrical circuits as an interface using a mechanical assembly. The connection may be temporary, as for portable equipment, require a tool for assembly and removal, or serve as a permanent electrical joint between two wires or...

s and source internal resistance
Internal resistance
A practical electrical power source which is a linear electric circuit may, according to Thévenin's theorem, be represented as an ideal voltage source in series with an impedance. This resistance is termed the internal resistance of the source. When the power source delivers current, the measured...

s are undesired as they reduce the supplied voltage while voltage drops across loads and other electrical
Electrical element
Electrical elements are conceptual abstractions representing idealized electrical components, such as resistors, capacitors, and inductors, used in the analysis of electrical networks...

 and electronic
Electronic component
An electronic component is a basic electronic element and may be available in a discrete form having two or more electrical terminals . These are intended to be connected together, usually by soldering to a printed circuit board, in order to create an electronic circuit with a particular function...

 elements are useful and desired.

In electrical wiring
Electrical wiring
Electrical wiring in general refers to insulated conductors used to carry electricity, and associated devices. This article describes general aspects of electrical wiring as used to provide power in buildings and structures, commonly referred to as building wiring. This article is intended to...

, national and local electrical code
Electrical code
An electrical code is a set of regulations for electrical wiring. The intention of an electrical code is to provide standards to ensure electrical wiring systems that are safe and unlikely to produce either electric shock or fires. Electrical codes are usually devised by national or international...

s may set guidelines for maximum voltage drop allowed in a circuit conductors, to ensure reasonable efficiency of distribution and proper operation of electrical equipment (the maximum permitted voltage drop varies from one country to another)http://www.electrical-installation.schneider-electric.com/voltage-drop.htm.