How do i calculate the current flow in a domestic mains circuit?
I remember the ohms law triangle from school, V I R and i know there is one for power (watts) calculations, i researched this online although i have since forgot how that one is layed out ? In any case i thought it was W/V=I, so for my electrical item this would be 600/240=2.5 amps However on the item itself there are 2 ratings- 3 amps and 6.2 amps clearly 3 amps refers to my above calculation plus a safety margin, where does 6.2 amps arise from- there is reference to the cos value, I vaguely know about including the cos calculation but do not know how it works or when it applies? I live in the UK in a standard residential property with a normal mains supply.......
2007-11-10 09:31:30 · 9 answers · asked by nurnord 7 in Science & Mathematics ➔ Engineering
The 6.2 may apply to running the device wired for 120 Volt power (USA).
2007-11-10 10:06:45 · answer #1 · answered by Tim C 7 · 1⤊ 1⤋
Your calculation seems fine for relating "apparent power" and RMS current/voltage.
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Tim C might be on the right track.
Think craw's got the "cos" bit figured
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Some idea of what the item is might give some clues. Does the item contain an electrical motor?
Most devices have a inrush current, when first switched on, that's larger than when it's been running a short while.
Maybe the larger figure is an inrush current, and the smaller the normal running current.
For most devices it settles down very quickly, but for devices such as electric motors, it can take some time (seconds ?) to decay to "normal" level. Fuses can normally only cope with a tiny time of over current for them to blow. In situations where needed time-delay fuses can be specified, to allow the current to settle down, and still provide protection from over-current/short-circuit.
Is "cos value" (trigonometric cos function?) something to do with the reactive power. I know it too can be important when dealing with electric motors?
2007-11-10 11:30:06 · answer #2 · answered by Steve C 6 · 0⤊ 0⤋
The cos (theta) is the phase angle. In an AC circuit, the power is not constant. It is a sinusoidal wave. If you want exact power at a moment in time, you will need to know where you are measuring in relation to the wave. We usually, say that theta is zero, because cos (theta)= 1, makes life easy.
2007-11-12 05:48:14 · answer #3 · answered by Ron L 2 · 0⤊ 0⤋
230/240 volts is the rms value as ac is used and current and voltage vary sinusoidally(as sin/cos value) so peak value of current/voltage are 1.4 times bigger than rms value but don't know where 6.2 amps comes from.
2.5x1.4 gives 3.5 not 6.2
2007-11-10 10:09:51 · answer #4 · answered by Clint 6 · 0⤊ 0⤋
your calculation is right i(current)=p(power in watts)divided by v(nominal cvoltage)except now to conform to european standards voltage(v)is now taken as being 230.it doesnt make a lot of difference 2.6amps but it keeps you right.
2007-11-10 09:55:13 · answer #5 · answered by dodgyspark 4 · 0⤊ 0⤋
your right with ohms law for your current calculation, the cos calculation is for power factor correction. try this link
http://www.informit.com/articles/article.aspx?p=101617&rl=1
2007-11-10 10:04:10 · answer #6 · answered by craw 2 · 1⤊ 0⤋
Yeah you are right, because I know P = I x I x R and V = I x R so P = I x V.
2007-11-10 10:00:19 · answer #7 · answered by chris 3 · 0⤊ 0⤋
E=m times c squared.
2007-11-10 10:44:28 · answer #8 · answered by nckjeanpierre 2 · 0⤊ 2⤋
You already know the answer... you just don't believe you do....Ask yourself how the people who worked out what you say in your question?
2007-11-10 09:42:19 · answer #9 · answered by Anonymous · 0⤊ 2⤋