|
|
| (One intermediate revision by one other user not shown) |
| Line 1: |
Line 1: |
| '''Voltage drop''' describes how the supplied [[energy]] of a [[voltage]] source is reduced as [[electric current]] moves through the passive elements (elements that do not supply voltage) of an [[electrical]] [[electrical network|circuit]]. Voltage drops across [[internal resistance]]s of the source, across [[Electrical conductor|conductors]], across [[Electrical contact|contacts]], and across [[Electrical connector|connectors]] are undesired; supplied energy is lost (dissipated). Voltage drops across [[Electrical load|loads]] and across other active circuit elements are desired; supplied energy performs useful work. Recall that voltage represents energy per unit [[Electric charge|charge]]. For example, an electric space heater may have a resistance of ten [[ohm]]s, and the wires which supply it may have a resistance of 0.2 ohms, about 2% of the total circuit resistance. This means that approximately 2% of the supplied voltage is lost in the wire itself. Excessive voltage drop may result in unsatisfactory operation of, and damage to, electrical and electronic equipments.
| | Hi there. Let me start by introducing the author, her title is Sophia. To play lacross is some thing I truly appreciate performing. My wife and I live in Mississippi but now I'm contemplating other options. I am an invoicing officer and I'll be promoted quickly.<br><br>Here is my web-site ... [http://srncomm.com/blog/2014/08/25/relieve-that-stress-find-a-new-hobby/ free psychic reading] |
| | |
| National and local [[electrical code]]s may set guidelines for the maximum voltage drop allowed in [[electrical wiring]], to ensure 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]. In electronic design and power transmission, various techniques are employed to compensate for the effect of voltage drop on long circuits or where voltage levels must be accurately maintained. The simplest way to reduce voltage drop is to increase the diameter of the conductor between the source and the load, which lowers the overall resistance. More sophisticated techniques use active elements to compensate for the undesired voltage drop.
| |
| | |
| ==Voltage drop in direct-current circuits: resistance==
| |
| | |
| [[File:Line voltage diagram.jpg||right|thumb|500px|<center>The local voltages along a long line decrease gradually from the source to the load</center>]]
| |
| | |
| Consider a direct-current circuit with a nine-volt [[direct current|DC]] source; three [[resistor]]s of 67 [[ohm]]s, 100 ohms, and 470 ohms; and a light bulb—all connected in [[Series circuit|series]]. The DC source, the conductors (wires), the resistors, and the light bulb (the [[electrical load|load]]) all have [[Electrical resistance|resistance]]; all use and dissipate supplied energy to some degree. Their physical characteristics determine how much energy. For example, the DC resistance of a conductor depends upon the conductor's length, cross-sectional area, type of material, and temperature.
| |
| | |
| If you measure the voltage between the DC source and the first resistor (67 ohms), you will notice the voltage potential at the first resistor is slightly less than nine volts. The current passes through the conductor (wire) from the DC source to the first resistor; as this occurs, some of the supplied energy is "lost" (unavailable to the load), due to the resistance of the conductor. Voltage drop exists in both the supply and return wires of a circuit. If you measure the voltage across each resistor, you will measure a significant number. That represents the energy used by the resistor. The larger the resistor, the more energy used by that resistor, and the bigger the voltage drop across that resistor.
| |
| | |
| You can use [[Ohm's Law]] to verify voltage drop. In a DC circuit, voltage equals current multiplied by resistance. <math>V = I R</math>. Also, [[Kirchhoff's circuit laws]] state that in any DC circuit, the sum of the voltage drops across each component of the circuit is equal to the supply voltage.
| |
| | |
| ==Voltage drop in alternating-current circuits: impedance==
| |
| | |
| In [[alternating current|alternating-current]] circuits, opposition to current flow does occur because of resistance (just as in direct-current circuits). Alternating current circuits also present a second kind of opposition to current flow: [[Electrical reactance|reactance]]. This "total" opposition (resistance "plus" reactance) is called [[Electrical impedance|impedance]]. The impedance in an alternating-current circuit depends on the spacing and dimensions of the elements and conductors, the frequency of the alternating current, and the magnetic permeability of the elements, the conductors, and their surroundings.
| |
| | |
| The voltage drop in an AC circuit is the product of the current and the impedance (''Z'') of the circuit. Electrical impedance, like resistance, is expressed in ohms. Electrical impedance is the [[Vector (geometric)|vector]] sum of [[electrical resistance]], [[capacitive reactance]], and [[inductive reactance]]. It is expressed by the formula <math>E = I Z</math>, analogous to [[Ohm's law]] for direct-current circuits.
| |
| | |
| ==Voltage drop in building wiring==
| |
| Most circuits in a house do not have enough current or length to produce a high voltage drop. In the case of very long circuits, for example, connecting a home to a separate building on the same property, it may be necessary to increase the size of conductors over the minimum requirement for the circuit current rating. Heavily-loaded circuits may also require a cable size increase to meet voltage drop requirements in wiring regulations.
| |
| | |
| Wiring codes or regulations set an upper limit to the allowable voltage drop in a branch circuit. In the United States, the 2005 [[National Electrical Code]] (NEC) recommends no more than a 5% voltage drop at the outlet.<ref>National Fire Protection Association, ''National Electrical Code, 2005 edition'' Quincy MA, FPN 4 to rule 210.19</ref> The Canadian electrical code requires no more than 5% drop between service entrance and point of use.<ref>Rick Gilmour et al., editor, Canadian Electrical Code Part I, Nineteenth Edition, C22.1-02 Safety Standard for Electrical Installations, Canadian Standards Association, Toronto, Ontario Canada (2002) ISBN 1-55324-600-X {{Please check ISBN|reason=Check digit (X) does not correspond to calculated figure.}}, rule 8-102</ref> UK regulations limit voltage drop to 4% of supply voltage. Following changes to the BS7671:2008 on consumers' installation, the following has become in force since 1 July 2008:
| |
| <!-- and if you have an English-language electrical ''for'' code that doesn't set a voltage drop limit, tell us about it! -->
| |
| | |
| {| class="wikitable"
| |
| |-
| |
| ! Type of Supply
| |
| ! Voltage drop lighting
| |
| ! Voltage drop other
| |
| |-
| |
| | [[Distribution Network Operator|DNO]]
| |
| | 3%
| |
| | 5%
| |
| |-
| |
| | Private
| |
| | 6%
| |
| | 8%
| |
| |}
| |
| | |
| Voltage drop of a branch circuit is readily calculated, or less accurately it can be measured by observing the voltage before and after applying a load to the circuit. Excessive voltage drop on a residential branch circuit may be a sign of insufficiently sized wiring or of other faults within the wiring system, such as high resistance connections.
| |
| | |
| Note: voltage drops for installations are specified from the point of common coupling (i.e. where the utility supply is connected to the premises) to the point at which the electrical load is connected<ref>{{cite web|title=Voltage Drop in Installations|url=http://myelectrical.com/opinion/entryid/87/voltage-drop-in-installations-concepts|work=Voltage Drop in Installations - Concepts|publisher=myelectrical.com|accessdate=8 October 2011}}</ref>
| |
| | |
| ==How to calculate voltage drop==
| |
| In situations where the circuit conductors span large distances, the voltage drop is calculated. If the voltage drop is too great, the circuit conductor must be increased to maintain the current between the points. The calculations for a single-phase circuit and a three-phase circuit differ slightly.
| |
| | |
| | |
| '''Single-phase voltage drop calculation:
| |
| | |
| | |
| [[File:Voltage Drop Calc - Single Phase.png|425px|]]
| |
| | |
| | |
| '''Three-phase voltage drop calculation:'''
| |
| | |
| | |
| [[File:Voltage Drop Calculation - 3 phase.png|425px|]]
| |
| | |
| | |
| <big>OR 3<big>ø</big>VD = (SQRT(3)*L*R*I)/1000</big>
| |
| | |
| '''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.
| |
| | |
| '''Important Note: According to NEC 215.2(A)(4) informational note No. 2, the voltage drop for feeders should not exceed 2% and the voltage drop for branch circuits should not exceed 3%, for efficient operation.'''<ref>{{cite web|title=How to Calculate Voltage Drop|url=http://www.electrical-design-tutor.com/voltagedropcalculation.html|work=How to Calculate Voltage Drop}}</ref>
| |
| | |
| ==Using higher voltages==
| |
| Over long distances, larger conductors become expensive, and it is preferable to redesign the circuit to operate at a higher voltage. Doubling the voltage halves the current required to deliver the same amount of power, halving the voltage drop, and an additional doubling in efficiency is realized because that drop is a smaller fraction of the total voltage.
| |
| | |
| This is the motivation for commercial [[high voltage]] [[electrical power distribution]], and for the use of the +12 V [[power supply rail]] for high-power loads in modern [[personal computer]]s.
| |
| | |
| ==See also==
| |
| {{Portal|Electronics}}
| |
| *[[Electrical distribution]]
| |
| *[[Electrical resistance]]
| |
| *[[Kirchhoff's voltage law]]
| |
| *[[Electrical conduction]]
| |
| *[[Ground loop (electricity)]]
| |
| *[[Power cable]]
| |
| *[[Mesh analysis]]
| |
| | |
| ==References==
| |
| <references />
| |
| *Electrical Principles for the Electrical Trades (Jim Jennesson) 5th edition
| |
| | |
| ==External links==
| |
| *[http://mc-group.ca/download.htm Freeware NEC Tables, CEC Tables and Electrical Calculation for your PC]
| |
| *[http://www.engineersedge.com/instrumentation/voltage_drop_calculator/wire_voltage_drop_calculator_12928.htm Voltage Drop Calculator]
| |
| *[http://www.mypq.net/tools/voltagedrop.asp EPRI Power Quality - Voltage Drop Calculator]
| |
| *[http://wiki.diyfaq.org.uk/index.php?title=Cables#Voltage_Drop Voltage drop of British mains cables]
| |
| * [http://myelectrical.com/tools/cable-sizing-calculator BS 7671:2008 Cable Sizing Tool]
| |
| | |
| [[Category:Electricity]]
| |
| [[Category:Electrical parameters]]
| |
| [[Category:Cables]]
| |
Hi there. Let me start by introducing the author, her title is Sophia. To play lacross is some thing I truly appreciate performing. My wife and I live in Mississippi but now I'm contemplating other options. I am an invoicing officer and I'll be promoted quickly.
Here is my web-site ... free psychic reading