dana@locus.com (Dana H. Myers) (04/27/91)
I wrote:
I know I'm the one who claimed that power is dissipated in capacitors a
while back (ugh!), but I do not believe 120VRMS is 340V p-p. It is 170V p-p.
To which sidney@coed.coastal.ufl.edu replied:
The 120vrms power is 340v p-p. The voltage equation for our 120 volt
system is 120*sin(377t). The rms value is the square root of the integral
of the voltage squared over a full period. For sine wave voltages this
works out to .707 * the peak voltage. For 120vrms power this is
.707 * 170 = 120 volts. The 170 volt peak voltage occurs on both the
positive and negative portions of the sin wave. Thusly the peak to peak
voltage is 340V not 170.
And now I write:
Oh goodness, I've done it again.
--
* Dana H. Myers KK6JQ | Views expressed here are *
* (213) 337-5136 | mine and do not necessarily *
* dana@locus.com | reflect those of my employer *myers@hpfcdj.HP.COM (Bob Myers) (04/30/91)
>The 120vrms power is 340v p-p. The voltage equation for our 120 volt >system is 120*sin(377t). The rms value is the square root of the integral ^^^ I can't believe it's talking so long to get this right! Care to take another shot, with the hint that the "120V" is an *RMS* value? Bob Myers KC0EW HP Graphics Tech. Div.| Opinions expressed here are not Ft. Collins, Colorado | those of my employer or any other myers@fc.hp.com | sentient life-form on this planet.
dam@dcs.glasgow.ac.uk (David Morning) (05/02/91)
myers@hpfcdj.HP.COM (Bob Myers) writes:
]>The 120vrms power is 340v p-p. The voltage equation for our 120 volt
]>system is 120*sin(377t). The rms value is the square root of the integral
] ^^^
]I can't believe it's talking so long to get this right! Care to take
]another shot, with the hint that the "120V" is an *RMS* value?
Err..... how about 340*sin(314t)... No?
Daveraoul@eplunix.UUCP (Nico Garcia) (05/02/91)
In article <17660158@hpfcdj.HP.COM>, myers@hpfcdj.HP.COM (Bob Myers) writes: > >The 120vrms power is 340v p-p. The voltage equation for our 120 volt > >system is 120*sin(377t). The rms value is the square root of the integral My oscilloscope says it's 320 V p-p. This means our output voltage is 160 V * sin( 377 * t + delta) 1/2 of p-p 2 * Pi * 60 cycles time offset And, 160 * 2^1/2 = 113 Volts. OK? In a perfect 120 Volts RMS world, it would be 339.4 Volts p0p. Are we all settled now? Thank you. We now return you to your regularly scheduled newsgroup. -- Nico Garcia Designs by Geniuses for use by Idiots eplunix!cirl!raoul@eddie.mit.edu
raoul@eplunix.UUCP (Nico Garcia) (05/02/91)
In article <1071@eplunix.UUCP>, raoul@eplunix.UUCP (Nico Garcia) writes: > My oscilloscope says it's 320 V p-p. This means our output voltage is > 160 V * sin( 377 * t + delta) > 1/2 of p-p 2 * Pi * 60 cycles time offset > And, 160 * 2^1/2 = 113 Volts. OK? In a perfect 120 Volts RMS world, it would > be 339.4 Volts p0p. Gods, even *I* did it. 160 * (1/2)^1/2 = 113 Volts. So, we all get mixed up in this stuff we know so well.... -- Nico Garcia Designs by Geniuses for use by Idiots eplunix!cirl!raoul@eddie.mit.edu
tomb@hplsla.HP.COM (Tom Bruhns) (05/02/91)
myers@hpfcdj.HP.COM (Bob Myers) writes: > I can't believe it's talking so long to get this right! Care to take ^^^^^^^ I can't believe it's taking so long, either! (Gosh, Bob, maybe that _wasn't_ a typo!) > another shot, with the hint that the "120V" is an *RMS* value? ^^^^ Maybe the writer lives in an area of continual brown-outs. (And slightly-higher-than-normal line frequency.) ;-) ;-)
tomb@hplsla.HP.COM (Tom Bruhns) (05/03/91)
dam@dcs.glasgow.ac.uk (David Morning) writes: > Err..... how about 340*sin(314t)... No? I'd like to nominate Dave to the order of the Golden Electron. Someone finally posted it right!
rex@cs.su.oz (Rex Di Bona) (05/08/91)
In article <12900002@hpavla.avo.hp.com> devlin@hpavla.avo.hp.com (Lee Devlin) writes: > > Cliff Stein writes: > > > >What's the purpose of polarized wall outlets with an AC > >signal? I don't understand. Is it really bad to force > >something to plug in the wrong way? > > >I am serious. With a real AC signal (sinusoidal waves) I can see no reason > >at all for it. How can the electrical equipment tell? > I came to the conclusion that they are trying to keep the internal fuse > in the hot line so that, if it blows when there's a short against the > enclosure, the enclosure won't be sitting at line voltage. This would be > the case if the internal fuse were in the neutral line. That is the only > reason I can see for using 2-prong polarized plugs. For this scheme to > work, the electrician has to have wired the house correctly (left = line, > right = neutral). > > Lee Devlin The three wires in an AC General Purpose Outlet (those wall sockets) are the active (red or brown), neutral (light blue or black), and earth (green/yellow). Under IEC and CEE regulations yellow/green is ALWAYS earth, and if there is a neutral it is light blue, and the rest are available for actives. It is the active conductor that has the current 'flowing' in it, and your appliance uses this by letting the current return via the neutral conductor. The neutral conductor will provide no current of its own, and is usually joined to earth. If you only have two pins in the socket they will be active and neutral (in Australia the active is on the left, when looking from the plug side). Now, if a break down occurs it will occur in one of three ways, either (1) the circuit is broken, ie, a conductor breaks, or (2) part of the circuit shorts out and extra current flows (to either neutral or earth), or finally, (3) metallic (well, usually metallic) parts are brought into contact with one of the conductors, and are accessible to the user. If 1 occurs then there is no problem. The current stops flowing, and you fix the device. If 2 occurs then the protective device for the house supply should cut off the current as excessive current is being drawn, and the conductors may overheat and ignite. If 3 occurs then there is a dangerous situation, no apparent fault exists, but current may be conducted if either a source (unlikely) or sink (very likely, ie you) comes into contact with the device. This moves the fault into category 2 and we hope the house device activates. Now, it is totally possible that the house protective device can supply a LOT of current. Circuit breakers that allow 30A before breaking are common, so you can put 240V into anything above 8 ohms and not reach that 30 amps. (actually thats' RMS, and the peak is higher, giving a max resistance of about 11 ohms before the breaker will trip). Now, a person is usually higher than 12 ohms, so an additional protective device is added to the circuit. This protective device must go into the active conductor to be effective, ie, the current that is killing you is going active->device->you->earth and nowhere near the neutral conductor. This is why the plugs are polarised. To ensure that the additional protective device is in the right conductor. Now, I would hope that a metallic case would be earthed. Only with doubly earthed devices should there be no earth wire. Good audio equipment is, however, usually double insulated to reduce the hum formed by earth loops. In Australia the installation of electric wiring is controlled by a specified standard, AS3000-1986 SAA WIRING RULES. 0.5.58 Insulation, double: A live part shall be regarded as separated from non-current-carrying metal parts by double insulation only if two layers of insulating material complying with the appropriate requirements of AS 3100 intervene between the live part and such metal parts. The layer of insulation adjacent to live parts is referred to as 'functional insulation' the second layer is referred to as 'protective insulation'. (The symbol for double insulation is a square within a square) 5.3.8.1 Double insulation: general. Equipment complying with the requirements of AS 3100 for double insulation need not be earthed. 5.3.8.3 Internal equipment wiring. Conductors within equipment having double insulation shall be protected, secured, or insulated so that, if any one conductor becomes detached from its termination, neither the conductor nor its functional insulation can come into contact with accessible metal. The attachment of one conductor to another by tying, lacing, clipping or the like, in such a manner as to prevent either conductor coming into contact with accessible metal if it becomes detached from its termination, shall be deemed to comply with this requirement. This means that we don't want to allow (3) to happen, and so you will also see no fuse on a double insulated device. -------- Rex di Bona (rex@cs.su.oz.au) Penguin Lust is NOT immoral
chaplin@keinstr.uucp (chaplin) (05/09/91)
In article <12900002@hpavla.avo.hp.com> devlin@hpavla.avo.hp.com (Lee Devlin) writes: >For this scheme [polarized line cord plugs] to >work, the electrician has to have wired the house correctly (left = line, >right = neutral). > >Lee Devlin Polarized plugs (and outlets) don't know "left" and "right." They know "wide blade (hole)" and "narrow blade (hole)." Hot may be on the left or the right, depending upon how whoever installed the outlet, or how your head happens to be positioned relative the the earth. Regardless, a properly wired polarized outlet will have hot on the narrow hole and neutral on the wide hole. -- Roger Chaplin / Instruments Division Engineering / uunet!keinstr!chaplin CI$: 76307,3506 / voice: (216) 498-2815 / FAX: (216) 248-6168 "In the last analysis the customer is the independent auditor. In the merciless light of real use, every flaw will show." - Frederick P. Brooks, Jr.
edhall@rand.org (Ed Hall) (05/11/91)
In article <2399@cluster.cs.su.oz.au> rex@cluster.cs.su.oz (Rex Di Bona) writes: >The three wires in an AC General Purpose Outlet (those wall sockets) >are the active (red or brown), neutral (light blue or black), and >earth (green/yellow). Careful! Although the ground wire is generally green in the US, the hot wire is frequently black, *not* the neutral, which is generally white. Needless to say, what is standard in Australia (or the US) may not be elsewhere. -Ed Hall edhall@rand.org
adrian@cs.hw.ac.uk (Adrian Hurt) (05/13/91)
In article <1991May10.202150.6785@rand.org> edhall@rand.org (Ed Hall) writes: >In article <2399@cluster.cs.su.oz.au> rex@cluster.cs.su.oz (Rex Di Bona) writes: >>The three wires in an AC General Purpose Outlet (those wall sockets) >>are the active (red or brown), neutral (light blue or black), and >>earth (green/yellow). > >Careful! Although the ground wire is generally green in the US, the hot >wire is frequently black, *not* the neutral, which is generally white. >Needless to say, what is standard in Australia (or the US) may not be >elsewhere. I seem to be suffering from deja vu. Wasn't this discussed a little while ago? Here's the table I was given by our safety office: 2 wire 3 wire Live Neutral | Live Neutral Earth -----------------------------------+------------------------------------- U.K. (new) Brown Blue | Brown Blue Green and Yellow | U.K. (old) Red Black | Red Black Green | Denmark Black* Blue | Brown/ Blue Green and Yellow | Black Finland Black/ Blue | Brown Blue Green and Yellow | Greece Any Grey | Any Grey Yellow except | except Grey, | Grey, Yellow, | Yellow, or Blue | or Blue | Japan Black White | Black White Red | Poland Black* Blue | Black Blue Green and Yellow | Switzerland Any Any | Brown Blue Green and Yellow except except | Yellow Yellow | or Blue or Red | | U.S.A. and Black* White | Black White Green or Canada or Grey | or Grey Green and Yellow *Black for live in 2-core cords is now being replaced by Brown. My notes: 1. If you see green, yellow or a combination thereof, it's almost certainly earth. 2. If you see blue, it's almost certainly neutral. 3. If you see brown, it's almost certainly live. 4. What the black wire does, depends on what other colours are present. If there's a white or grey wire present, then black is live, and white is neutral. If there are two wires (black and red) or three wires (black, red and green) then black is neutral. If there are three wires (black, red and white) then black is live, white is neutral and red is earth! 5. The jokers in the pack are Japan (red earth), and Greece and Switzerland. I've also seen a Chinese cooker with two white wires. China isn't included in the above list, because it isn't in the list in my booklet. Presumably the Chinese use electrical devices as a form of population control - the cooker in question, a small portable one, had a metal frame and no earth connection. "Keyboard? How quaint!" - M. Scott Adrian Hurt | JANET: adrian@uk.ac.hw.cs UUCP: ..!ukc!cs.hw.ac.uk!adrian | ARPA: adrian@cs.hw.ac.uk
tell@oscar.cs.unc.edu (Stephen Tell) (05/15/91)
In article <2953@odin.cs.hw.ac.uk> adrian@cs.hw.ac.uk (Adrian Hurt) writes: >In article <1991May10.202150.6785@rand.org> edhall@rand.org (Ed Hall) writes: >>In article <2399@cluster.cs.su.oz.au> rex@cluster.cs.su.oz (Rex Di Bona) writes: >>>The three wires in an AC General Purpose Outlet (those wall sockets) >>>are the active (red or brown), neutral (light blue or black), and >>>earth (green/yellow). >> >>Careful! Although the ground wire is generally green in the US, the hot >>wire is frequently black, *not* the neutral, which is generally white. >>Needless to say, what is standard in Australia (or the US) may not be >>elsewhere. >Here's the table I was given by our safety office: [Nice table deleted for brevity] >U.S.A. and Black* White | Black White Green or >Canada or Grey | or Grey Green and Yellow > >*Black for live in 2-core cords is now being replaced by Brown. > >My notes: >1. If you see green, yellow or a combination thereof, it's almost certainly >earth. >2. If you see blue, it's almost certainly neutral. Carefull!! In larger buildings in the US, 120/208 volt 3-phase service uses Black, Red, and Blue for the three hot wires, with the standard white for neutral and green for brown. I've seen such an installation (build less than two years ago, passed inspection) that kept the hot wire in its original color to identify which phase it was associated with even when there were no other hot wires in that conduit. So, an outlet could be fed by blue (hot), white (neutral), and green (ground). In the same building, yellow, brown, and orange are the three hot wires for 277/480 volt 3-phase. I don't think 277/480 is ever supposed to share a conduit with 120/208, though. I have seen it advised to "re-code" the white wire to blue with electrical tape when using both wires in two-conductor cable as hots, like to a switch. >3. If you see brown, it's almost certainly live. >4. What the black wire does, depends on what other colours are present. If >there's a white or grey wire present, then black is live, and white is >neutral. If there are two wires (black and red) or three wires (black, red >and green) then black is neutral. If there are three wires (black, red and >white) then black is live, white is neutral and red is earth! In the US, red/black/green could be 240 volts with ground and no neutral (two hots). Red/black/white could be 120/140 (or 120/208), although there really should be a neutral in there). >5. The jokers in the pack are Japan (red earth), and Greece and Switzerland.... Thanks for the useful info, but I think the real lesson should be: If you're planning to mess around with AC power, know what you're doing, have a voltmeter, know how to use it, and be extremly careful. Especially in another country or in an old building. > Adrian Hurt | JANET: adrian@uk.ac.hw.cs > UUCP: ..!ukc!cs.hw.ac.uk!adrian | ARPA: adrian@cs.hw.ac.uk -- Steve Tell tell@cs.unc.edu H: +1 919 968 1792 #5L Estes Park apts CS Grad Student, UNC Chapel Hill. W: +1 919 962 1845 Carrboro NC 27510 Duke Blue Devils: 1991 NCAA Basketball National Champions! We're Number 1 !! UNLV 90-91 record: "34 and DUKE."