Post by thread:[OT] 240V in USA

The 120/240 single phase power ( two lines and a neutral) basically goes into ev ery home. The connection is simply a centre tapped transformer. Low power appliances (TV, lights, ...) run on 120 V. Higher power loads (stove, clothes dryer, electric furnace,...) run on the 240 V supply. For light/medium industrial the power system typically uses 120/208 or 277/480 Volt, 3 phase power. In Canada we use 120/208 or 346/600 Volt 3 phase. Hope this answers your question. ----Original Message----- >From: Leo van Loon <.....sbb.simpeltronKILLspam@spam@TIP.NL> >To: PICLISTKILLspamMITVMA.MIT.EDU >Subject: [OT] 240V in USA >Reply-To: pic microcontroller discussion list <.....PICLISTKILLspam.....MITVMA.MIT. EDU> >Date: Tuesday, July 21, 1998 05:15 > >Dear friends, > >In another mailinglist a member told about a two-phase 120V net with 180 >degrees phase difference in parts of the US. I do not understand how high >power induction motors can be used with such an electricity supply. Three >phase rotary currant was invented for this type of motors. >Can anybody from the States tell me about the finesses of this type of >electricity supply? > >Leo van Loon >SBB simpeltronics >Netherlands >tel +31 (0481) 450034 >fax+31 (0481) 450051 >mail EraseMEsbb.simpeltronspam_OUTTakeThisOuTtip.nl >url http://www.sbb-simpeltronics.nl >SBB simpeltronics ontwikkelt technische projecten voor basisschool en >basisvorming. >SBB simpeltronics develops technical projects for children in primary and >secondary education. >

Thanks, This answers my question. The system is quite complicated in comparison with the European only 230V three phase. Has that a historical reason? Leo van Loon -----Oorspronkelijk bericht----- Van: Dennis O'Brien <deobrienspam_OUTSYMPATICO.CA> Aan: @spam@PICLISTKILLspamMITVMA.MIT.EDU <KILLspamPICLISTKILLspamMITVMA.MIT.EDU> Datum: dinsdag 21 juli 1998 14:58 Onderwerp: Re: [OT] 240V in USA >The 120/240 single phase power ( two lines and a neutral) basically goes into every home. The connection is simply a centre tapped transformer. > >Low power appliances (TV, lights, ...) run on 120 V. Higher power loads (stove, clothes dryer, electric furnace,...) run on the 240 V supply. > >For light/medium industrial the power system typically uses 120/208 or 277/480 Volt, 3 phase power. In Canada we use 120/208 or 346/600 Volt 3 phase. > >Hope this answers your question. > > >----Original Message----- > >From: Leo van Loon <RemoveMEsbb.simpeltronTakeThisOuTTIP.NL> > >To: spamBeGonePICLISTspamBeGoneMITVMA.MIT.EDU > >Subject: [OT] 240V in USA > >Reply-To: pic microcontroller discussion list <TakeThisOuTPICLISTEraseMEspam_OUTMITVMA.MIT.EDU> > >Date: Tuesday, July 21, 1998 05:15 > > > >Dear friends, > > > >In another mailinglist a member told about a two-phase 120V net with 180 > >degrees phase difference in parts of the US. I do not understand how high > >power induction motors can be used with such an electricity supply. Three {Quote hidden}> >phase rotary currant was invented for this type of motors. > >Can anybody from the States tell me about the finesses of this type of > >electricity supply? > > > >Leo van Loon > >SBB simpeltronics > >Netherlands > >tel +31 (0481) 450034 > >fax+31 (0481) 450051 > >mail RemoveMEsbb.simpeltronTakeThisOuTtip.nl > >url http://www.sbb-simpeltronics.nl > >SBB simpeltronics ontwikkelt technische projecten voor basisschool en > >basisvorming. > >SBB simpeltronics develops technical projects for children in primary and > >secondary education. > > > >

Leo wrote: > Dear friends, > > In another mailinglist a member told about a two-phase 120V net with > 180 degrees phase difference in parts of the US. I do not understand > how high power induction motors can be used with such an electricity > supply. Three phase rotary currant was invented for this type of > motors. Can anybody from the States tell me about the finesses of > this type of electricity supply? Two phase was used in very old power systems, along with DC and other obsolete voltages. There are still areas of the US, mostly in the cores of older cities, that have these obsolete systems still operating on a few buildings. Hey, if it ain't broke, don't fix it, right? I know for a fact that Downtown St. Louis, MO has a few blocks with DC, and I think there is also a little two-phase. Probably way less than 1% of US buildings are wired this way. No new buildings are installed with these systems. Why they picked two phase 120v I do not know. -- Lawrence Lile "An Engineer is simply a machine for turning coffee into assembler code." Download AutoCad blocks for electrical drafting at: http://home1.gte.net/llile/index.htm

You can use 3 phase induction motors on single phase. I have three industrial quality machines in my shop that do very well. Put the 240 V across two of the motor leads, and run the third motor lead back to either of the 240 V supply through a large (50 mfd or so) oil-filled AC capacitor rated to at least 380V. The motor will begin turning in one direction or the other depending on what side the cap is connected to. Disconnect the cap when the motor reaches about 75% speed, it is for starting only. You will get only about 65% of the torque that the motor would give on 240V 3 Phase, but usually that is plenty. The 3 phase motor is almost indestructable, and used industrial equipment is a much better bargain than new single phase modern home shop equipment. There is a company that markets a box that does the automatic disconnect of the capacitor, called Phase-O-Matic, but two switches and the capacitor does just fine. John Shreffler. {Original Message removed}

Harold Hallikainen EraseMEharoldhallikainen.com Hallikainen & Friends, Inc. See the FCC Rules at http://hallikainen.com/FccRules and comments filed in LPFM proceeding at http://hallikainen.com/lpfm On Tue, 21 Jul 1998 11:15:05 +0200 Leo van Loon <RemoveMEsbb.simpeltronEraseMEEraseMETIP.NL> writes: {Quote hidden}>Dear friends, > >In another mailinglist a member told about a two-phase 120V net with >180 >degrees phase difference in parts of the US. I do not understand how >high >power induction motors can be used with such an electricity supply. >Three >phase rotary currant was invented for this type of motors. >Can anybody from the States tell me about the finesses of this type of >electricity supply? > This is generally only used in residential electric supplies. A single phase of the three phase power on the pole is run thru a transformer with a 240VAC center tapped secondary. We then have two hots and a grounded neutral. 240VAC single phase loads (like heating loads) are run between the two hots. Single phase loads are run hot to neutral. In industrial environments, we either have three phase delta or wye. The wye is used where there are a lot of 120VAC single phase loads, since they can be connected between any hot and neutral. You get 208VAC between any two hots, which is acceptable for many 240VAC single phase loads (though not all). Other places have a three phase delta connection where each transformer secondary is 240VAC. One of the secondaries has the center tap grounded and is used as a neutral. Single phase 120VAC and 240VAC loads use this secondary. The third lead (the wild phase) is 208 volts above ground. Sometimes we get an "open delta" with only two transformers. These are not favored much. Now, questions on European (and elsewhere) power. I've read about limitations on harmonic line current. Though I have not read the standards (IEC standars are expensive!), it appears these standards apply to equipment that draws more than 16 amps. We manufacture phase controlled light dimmers, which draw more than 16 amps. Is the 16 amp limitation (if I've read correctly) a recognition that below this current it is practical to use some sort of power factor correction and above it phase control is indeed the most efficient way to control large loads? I'd be interested in hearing more on this (regulation of power line harmonic current) anywhere in the world! Thanks! Harold _____________________________________________________________________ You don't need to buy Internet access to use free Internet e-mail. Get completely free e-mail from Juno at http://www.juno.com Or call Juno at (800) 654-JUNO [654-5866]

On Tue, 21 Jul 1998, Leo van Loon wrote: > Dear friends, > > In another mailinglist a member told about a two-phase 120V net with 180 > degrees phase difference in parts of the US. I do not understand how high > power induction motors can be used with such an electricity supply. Three > phase rotary currant was invented for this type of motors. > Can anybody from the States tell me about the finesses of this type of > electricity supply? I'm not in North America, but from what wire gauge I see used on the cables of equipment coming from there, I believe that they got the 240 V thing so they can have dryers & ovens that are *lighter* than their *power cables* ;). Most bigger household appliances for 110 Volts (toaster etc) have cables so thick you could use them to tie a small boat with (1500 W toaster @ 110 V ~= 14 Amps, against only 7 here @ 220 V). So someone saw the light and decided that people get to touch 'safe' 110 Volts, but large appliances will be powered with a more sensible 220 Volts, so the Copper mines don't get filthy rich on in-house wiring ;) perhaps this helps, Peter

On Tue, 21 Jul 1998 15:46:42 +0200 Morgan Olsson <RemoveMEmrtspam_OUTKILLspamINAME.COM> writes: >At 08:49 1998-07-21 -0400, you wrote: >>The 120/240 single phase power ( two lines and a neutral) basically >goes >into every home. The connection is simply a centre tapped transformer. >> >>Low power appliances (TV, lights, ...) run on 120 V. Higher power >loads >(stove, clothes dryer, electric furnace,...) run on the 240 V supply. > >What kind of wall outlet connectors are used? Various connectors are used, keyed to the current capacity of the circuit. For stoves and clothes driers a rather large plug maybe 2" across is used, rated 30 or 50A. Large window-mounted air conditioners use a plug about the same size as a 120V plug, only with the blades aligned differently (horizontal instead of vertical) so it is impossible to interchange. These are rated for 20 or 25A. Generally the 240-volt outlets are installed in specific places where the appliance is expected to stay, and have an individual circuit in the breaker box. Furnaces, water heaters, central air conditioners, etc. are wired in permanently. Most of the plugs are 3-wire, having the two hot wires and safety ground. Generally the appliances operate everything on 240V working between the two hot wires. In some cases the appliance derives a 120V circut between one hot wire and ground, which is allowed by many codes. There are also 4-wire plugs and sockets that seperate the ground and neutral circuits. _____________________________________________________________________ You don't need to buy Internet access to use free Internet e-mail. Get completely free e-mail from Juno at http://www.juno.com Or call Juno at (800) 654-JUNO [654-5866]

On Tue, 21 Jul 1998 10:22:11 -0400 John Shreffler <RemoveMEJohn.ShrefflerTakeThisOuTspamavenuetech.com> writes: >You can use 3 phase induction motors on single phase. I have >three industrial quality machines in my shop that do very well. >Put the 240 V across two of the motor leads, and run the >third motor lead back to either of the 240 V supply through >a large (50 mfd or so) oil-filled AC capacitor rated to at least >380V. The motor will begin turning in one direction or the >other depending on what side the cap is connected to. Disconnect >the cap when the motor reaches about 75% speed, it is for >starting only. You will get only about 65% of the torque that >the motor would give on 240V 3 Phase, but usually that is >plenty. For light duty use (and most home uses of industrial machines are quite light duty) this is fine. In industry, motors are often burned out by operating them (at full rating) without knowing that a phase has been lost, so it is essential to keep such operation light and intermittent. A more advanced technique uses another surplus 3-phase induction motor as a converter. The converter motor is started with a capacitor as described and just allowed to idle with no mechanical load. It will act as a "rotating transformer" and generate a fairly good rendition of the third phase. The three wires of the converter motor, two of which are the single phase power, form the 3-phase bus to the load. The converter motor should be considerably larger than the one in the machine tool. The motor(s) in the machine tool can then be used at nearly full rating. The standard controls can be used to start or reverse the load motors just as if they had 3-phase utility power. _____________________________________________________________________ You don't need to buy Internet access to use free Internet e-mail. Get completely free e-mail from Juno at http://www.juno.com Or call Juno at (800) 654-JUNO [654-5866]

Hi All, Yeah, I know, its something that I should probably know already, but I have never seen an explanation, so I'll ask anyway: Does anyone have a quick explanation on why it is better (more efficient?) to use 3 phases instead of two on industrial equipment? Thanks, Sean On Tue, 21 Jul 1998, Mike Keitz wrote: {Quote hidden}> On Tue, 21 Jul 1998 15:46:42 +0200 Morgan Olsson <EraseMEmrtspamspamBeGoneINAME.COM> writes: > >At 08:49 1998-07-21 -0400, you wrote: > >>The 120/240 single phase power ( two lines and a neutral) basically > >goes > >into every home. The connection is simply a centre tapped transformer. > >> > >>Low power appliances (TV, lights, ...) run on 120 V. Higher power > >loads > >(stove, clothes dryer, electric furnace,...) run on the 240 V supply. > > > >What kind of wall outlet connectors are used? > > Various connectors are used, keyed to the current capacity of the > circuit. For stoves and clothes driers a rather large plug maybe 2" > across is used, rated 30 or 50A. Large window-mounted air conditioners > use a plug about the same size as a 120V plug, only with the blades > aligned differently (horizontal instead of vertical) so it is impossible > to interchange. These are rated for 20 or 25A. Generally the 240-volt > outlets are installed in specific places where the appliance is expected > to stay, and have an individual circuit in the breaker box. Furnaces, > water heaters, central air conditioners, etc. are wired in permanently. > > Most of the plugs are 3-wire, having the two hot wires and safety ground. > Generally the appliances operate everything on 240V working between the > two hot wires. In some cases the appliance derives a 120V circut between > one hot wire and ground, which is allowed by many codes. There are also > 4-wire plugs and sockets that seperate the ground and neutral circuits. > > _____________________________________________________________________ > You don't need to buy Internet access to use free Internet e-mail. > Get completely free e-mail from Juno at http://www.juno.com > Or call Juno at (800) 654-JUNO [654-5866] >

Mike Kietz wrote: > >I know for a fact that Downtown St. Louis, MO has a few blocks with > >DC, and I think there is also a little two-phase. Probably way less > >than 1% of US buildings are wired this way. No new buildings are > >installed with these systems. > > How are these places energized? Directly from the power plant. It seems incredible that this system would still even be in place. I believe the utility is pressuring these guys to upgrade, and the NEC code would require an upgrade any time the building is renovated. > What's in homes now shouldn't be called two phase since its just > single phase available at two voltages. Probably it was done to > provide a choice of voltages, maybe it was thought that 240 V at > every wall socket would be too dangerous. There was a big argument 120V vs 240v, and DC versus AC in the elder days. The choice of 120V, 60Hz is unfortunate, because that is exactly the most dangerous voltage and frequency range for the human heart. Lower frequencies (like 50 HZ or DC) do not defribulate the heart as severely. Higher frequencies might be too fast for the heart muscles to react. Lower voltages (less than 50 volts) can't generate enough current through human skin to cause burns and stop your heart. Higher voltages (like 240) tend to knock you off or tend to make the muscles jerk so severely as to send the victim flying. Solution: Sue Edison and Tesla in court. -- Lawrence Lile "An Engineer is simply a machine for turning coffee into assembler code." Download AutoCad blocks for electrical drafting at: http://home1.gte.net/llile/index.htm

3-phase AC motors are much smaller and use less copper for the same torque than 1-phase AC motors, they also have less losses (are much more efficient) because the AC line provides the phase rotation, rather than something (capacitor, imped ance,etc.) in the motor providing phase rotation. For a given amount of power transmitted across a distance, you can use much less copper for the same losses with 3-phase (3-wire), and you can use lower voltage s = smaller, lighter insulators) because the wire is being used at the peak curr ent (peak of the sine wave, where most of the actual power is moved) three times as often. Finally with 3-phase, you can suffer the loss of one wire and still get apprecia ble power to the destination. Regards, Ron Fial ================================================= At 05:37 PM 7/21/98 -0400, you wrote: {Quote hidden}>Hi All, > >Yeah, I know, its something that I should probably know already, but I >have never seen an explanation, so I'll ask anyway: > >Does anyone have a quick explanation on why it is better (more >efficient?) to use 3 phases instead of two on industrial equipment? > >Thanks, > >Sean > >

At 08:49 AM 7/21/98 -0400, you wrote: >The 120/240 single phase power ( two lines and a neutral) basically goes into every home. The connection is simply a centre tapped transformer. > >Low power appliances (TV, lights, ...) run on 120 V. Higher power loads (stove, clothes dryer, electric furnace,...) run on the 240 V supply. > >For light/medium industrial the power system typically uses 120/208 or 277/480 Volt, 3 phase power. In Canada we use 120/208 or 346/600 Volt 3 phase. Also, most homes are configured to use both sides of the phases as evenly as possible. Andy ================================================================== Andy Kunz - Statistical Research, Inc. - Westfield, New Jersey USA ==================================================================

Hi Andy, Paul, and others who responded, Thanks for the explanation. I already understood that minimum current causes minimum wire heating (i^2R), but I guess I still don't understand why one couldn't just use a higher voltage instead of 3-phase. Using multiple phases doesn't increase the voltage between phases much over the single phase-to-ground voltage, does it? THe only outstanding reason that clearly makes sense to me is that the phases deliver the AC peaks in rotational order for motors. Thanks, Sean On Wed, 22 Jul 1998, Andy Kunz wrote: {Quote hidden}> > Does anyone have a quick explanation on why it is better (more > > efficient?) to use 3 phases instead of two on industrial equipment? > > Can we all say "I-squared R" together now?! > > Andy > > > ================================================================== > Andy Kunz - Statistical Research, Inc. - Westfield, New Jersey USA > ================================================================== >

On Wed, 22 Jul 1998 13:28:12 -0400 Sean Breheny <RemoveMEshb7KILLspamCORNELL.EDU> writes: >Hi Andy, Paul, and others who responded, > > >Thanks for the explanation. I already understood that minimum current >causes minimum wire heating (i^2R), but I guess I still don't >understand >why one couldn't just use a higher voltage instead of 3-phase. With three-phase, when peak current is flowing in one wire the returning current is evenly distributed between the other two wires. So the worst case of I^2 is occuring in only one wire at a time. In single phase, peak current flows through both wires. Increasing the voltage has practical limits. For a given voltage three phase can distribute more power. Using >multiple phases doesn't increase the voltage between phases much over >the >single phase-to-ground voltage, does it? It is increased by square root of 3, for example with 120V from each phase to ground the voltage between phases is 208V. Power transmission networks use a "delta" referenced system where no current intentionally flows through ground, it is all balanced between the phase wires. Look at a high-voltage power pole and note that the three live conductors are larger than the neutral conductor, which really serves only as a safety ground. The insulators only have to withstand the phase to ground voltage of course. >THe only outstanding reason that clearly makes sense to me is that the >phases deliver the AC peaks in rotational order for motors. It's real easy to build a three-phase generator, in fact you'd almost want to rather than a single phase machine because the windings can be more evenly distributed around the stator. I seem to remember that Tesla built multiple-phase induction motors first then struggled with how to make a single phase one work (I suppose to compete with DC, where "only two wires" would be a big selling point). Three phase techniques aren't limited to big industrial stuff. The alternator in a car is a three-phase generator with an internal diode bridge. Besides being easy to wind, the three phases provide better DC output since the output current never goes to zero. Losses in the diodes are also diminished compared to a single-phase bridge. Using 1.5 times more diodes, the unit can deliver 3 times the current. The larger "Brushless DC motors" found in disk drives, VCRs, etc. are also three-phase at heart. Small ones such as in CPU fans are usually two-phase. _____________________________________________________________________ You don't need to buy Internet access to use free Internet e-mail. Get completely free e-mail from Juno at http://www.juno.com Or call Juno at (800) 654-JUNO [654-5866]

Hi Mike, On Wed, 22 Jul 1998, Mike Keitz wrote: > With three-phase, when peak current is flowing in one wire the returning > current is evenly distributed between the other two wires. So the worst > case of I^2 is occuring in only one wire at a time. In single phase, > peak current flows through both wires. Increasing the voltage has > practical limits. For a given voltage three phase can distribute more > power. > Again, it is probably something obvious, but I can't figure out how this is any more efficient than just using separate wires carrying the same phase. In other words,in a single phase system: 2 wires, each with a 5 ohm resistance, for example, carrying 100 amps (one in one direction, the other for return): Power dissipated = 2 * 5 * 100^2 = 100,000 watts For three phase, 1 wire at 100 amps, with 5 ohms resistance, two wires, each at 50 amps, with 5 ohms resistance each: Power dissipated = 5 * 100^2 + 2 * 5 * 50^2 = 75, 000 watts For single (or dual) phase again, this time with one forward wire, and two return: power dissipated = 5 * 100^2 + 2 * 5 * 50^2 = 75,000 watts no different from the 3 phase system. Instead of using multiple wires, you could also just use thicker wire with two phase, which you couldn't do with 3-phase ( you must have at least three wires) > It is increased by square root of 3, for example with 120V from each > phase to ground the voltage between phases is 208V. Power transmission > networks use a "delta" referenced system where no current intentionally > flows through ground, it is all balanced between the phase wires. Look > at a high-voltage power pole and note that the three live conductors are > larger than the neutral conductor, which really serves only as a safety > ground. The insulators only have to withstand the phase to ground > voltage of course. Again, this doesn't quite make sense to me. If you stuck with two phase, you could still avoid using ground for a return, and instead of a root 3 (1.73) factor by which the voltage to ground is decreased, you would get a full factor of 2. {Quote hidden}> > It's real easy to build a three-phase generator, in fact you'd almost > want to rather than a single phase machine because the windings can be > more evenly distributed around the stator. I seem to remember that Tesla > built multiple-phase induction motors first then struggled with how to > make a single phase one work (I suppose to compete with DC, where "only > two wires" would be a big selling point). > > Three phase techniques aren't limited to big industrial stuff. The > alternator in a car is a three-phase generator with an internal diode > bridge. Besides being easy to wind, the three phases provide better DC > output since the output current never goes to zero. Losses in the diodes > are also diminished compared to a single-phase bridge. Using 1.5 times > more diodes, the unit can deliver 3 times the current. The larger > "Brushless DC motors" found in disk drives, VCRs, etc. are also > three-phase at heart. Small ones such as in CPU fans are usually > two-phase. These reasons (ease of motor/generator winding, better rectification) make the most sense to me. It seems to me that these are probably the REAL resons why 3-phase is used, because the other benefits which you and others mentioned seem to be only side benefits, which could be achieved using single or dual phase systems. Am I wrong? Sorry if it seems that I am getting into a very argumentative tone <G>. I really am just trying to get to the heart of why 3-phase is better than two or one. One last question, when voltage is stated in 3-phase systems, is it referring to the peak voltage to ground, peak voltage between phases, or an RMS voltage? Thanks again guys, Sean

Your calculation is a little bit wrong. 1 phase 100 A :Power dissipated = 2 * 5 * 100^2 = 100,000 watts 3 phase 100 A :Power dissipated = 3 * 5 * 33^2 = 16,666 watts All other calculations are not correct cause the currants are not right for AC. You may not simply add currants. There is no currant in the neutral lines in a symmetrical situation. Normally a 2-phase situation has 90 degrees phase difference between the phases. 2-phase with 180 degrees phase difference is essentially the same as 1-phase. To run an induction motor on 1-phase you have to create the second phase (90 degrees phase difference) with a capacitor or a short-circuit winding in the motor, or with some electronics Leo van Loon -----Oorspronkelijk bericht----- Van: Sean Breheny <shb7STOPspamspam_OUTCORNELL.EDU> Aan: spamBeGonePICLISTSTOPspamEraseMEMITVMA.MIT.EDU <KILLspamPICLISTspamBeGoneMITVMA.MIT.EDU> Datum: woensdag 22 juli 1998 23:23 Onderwerp: Re: [OT] 240V in USA >snip< >Thanks again guys, > >Sean > >

Sean Breheny wrote: > Again, it is probably something obvious, but I can't figure out how > this is any more efficient than just using separate wires carrying the > same phase. You are *quite right*. It isn't. Using the American system and comparing three phases at 120¡, each 120V to ground, with a split phase, centred on ground, 120V each side, the efficiency is basically the same. Each system requires the same insulation of each wire, and the total power in a balanced state is 120V times the total of the currents in the phase wires. Transformers and wires for either system are just as efficient. The advantage of using the third phase comes in the three areas previously specified: Motors, Generators and Rectifiers. Domestic consumers are largely un-fussed, but industry is a *big* user of electricity. Three- phase motors are simpler than four-phase (i.e., two balanced pairs at 90¡) and are the minimum necessary to convey rotary impulse. Railways (trams, trolley-buses and trains) use DC, where six-phase rectifiers make things so much easier (than rotary converters). But the most significant point is that the harmonic vibration content of the generators is reduced by using three phases. IOW, consider the forces on the shaft of a single phase generator - it is being loaded when the current peaks, unloaded when it nulls. Sort of like a hammer drill. Using a three-phase system, this effect is split among the three phases so that the harmonic content is virtually cancelled. -- Cheers, Paul B.

Hello PIC.ers, .. Sure. That's what a variable speed induction motor electronic inverter is. They have a 3-phase output, generated by PWM switching a DC rail rectified from the 1-phase supply. .. Other features added, are for varying the frequency (thus RPM), and boost at low freq., interlocks for safety, overload and the like. .. This is not OT. A local manufacturer uses the 16c73, and other PIC variants to run the smarts for this. .. FWIW the last ASR33 teletype we used had a name given it. `Chatanooga Choo Choo' Best regards, John >Date: Tue, 21 Jul 1998 12:15:23 -0400 >From: Mike Massen <EraseMEerazmusEraseMEWANTREE.COM.AU> >.Subject: Re: [OT] 240V in USA >Interesting stuff this about 240V. Here in Australia we also >have 240V (used to be 250V) in Western Australia several years ago. >So - does anyone know of a commercial single phase to 3-phase >converter (other than a motor/alternator) - about 2KW max ? .. .. email from John Sanderson at JS Controls, PO Box 1887, Boksburg 1460, Rep. South Africa Manufacturer & purveyor of laboratory force testing apparatus and related products and services. Tel/fax: Johannesburg 893 4154 Cellphone 082 453 4815

On Thu, 23 Jul 1998 08:30:24 +1000 "Paul B. Webster VK2BZC" <@spam@paulb@spam@spam_OUTmidcoast.com.au> writes: > Railways (trams, trolley-buses and trains) use DC, where six-phase >rectifiers make things so much easier (than rotary converters). Also, it's possible to combine delta connected transformers and wye connected transformers into full wave rectifiers and get a ripple frequency that is 12 times the line frequency. This was used in an AM broadcast transmitter made by Continental. The FCC at one time required AM stations to have hum and noise 45 dB below 100% modulation while FM stations were required to be 60 dB down. This AM had noise down about 65 dB. The only AM I've ever seen where you could hear tape hiss on the air. Harold Harold Hallikainen spamBeGoneharoldKILLspamhallikainen.com Hallikainen & Friends, Inc. See the FCC Rules at http://hallikainen.com/FccRules and comments filed in LPFM proceeding at http://hallikainen.com/lpfm _____________________________________________________________________ You don't need to buy Internet access to use free Internet e-mail. Get completely free e-mail from Juno at http://www.juno.com Or call Juno at (800) 654-JUNO [654-5866]

Rogerio Odriozola wrote: (quoting Martin) >> Sorry Mike, but there is never 240V across any two terminals in a >> standard NA wall socket. > Martin, Mike is right. He is talking about the large 20 amp., 50 amp. > 3-wire plugs. They do have 2 live and 1 ground. You can get 240 volts > out of the 2 live wires. The connector you are talking about (1 live, > 1 neutral, 1 ground) is for small 120 volt appliances, not large > ovens, water heaters etc. Proves to me that the U S of A is such a polyglot place that even many shall we hope, technically competent, people don't even know all the variations in power reticulation. I must go there sometime, even just to see all the power points (local vernacular for power outlet, GPO etc.)! -- Cheers, Paul B.

In the USA we use 220v, 2 phase on many motors up to about 5 hp as often found in air conditioner compressors. We call it 220v single phase to distinguish it from 3 phase, but you are correct, it is really two 120v lines out of phase. We do it this way just because 220 v single phase is all that is available in most residential neighborhoods. The single phase motor can be made almost as high starting torque as the 3 phase by using capacitors. The efficiency is about equal. A small 10 to 30 mfd is put across the start and run windings---mostly for power factor. A large, hundreds of mfd, is also across the same windings but is switched out when the motor is up to about 80% of rated speed. This is usually done by a "potential" relay which reads the back EMF. Hope this helps. 73 de Joe, N6YMD Leo van Loon wrote: {Quote hidden}> Dear friends, > > In another mailinglist a member told about a two-phase 120V net with 180 > degrees phase difference in parts of the US. I do not understand how high > power induction motors can be used with such an electricity supply. Three > phase rotary currant was invented for this type of motors. > Can anybody from the States tell me about the finesses of this type of > electricity supply? > > Leo van Loon > SBB simpeltronics > Netherlands > tel +31 (0481) 450034 > fax+31 (0481) 450051 > mail .....sbb.simpeltronspam_OUTtip.nl > url http://www.sbb-simpeltronics.nl > SBB simpeltronics ontwikkelt technische projecten voor basisschool en > basisvorming. > SBB simpeltronics develops technical projects for children in primary and > secondary education.

> Van: Sean Breheny <TakeThisOuTshb7.....TakeThisOuTCORNELL.EDU> > Aan: TakeThisOuTPICLISTKILLspamspamMITVMA.MIT.EDU > Onderwerp: Re: [OT] 240V in USA > Datum: dinsdag 21 juli 1998 23:37 > > Hi All, > > Yeah, I know, its something that I should probably know already, but I > have never seen an explanation, so I'll ask anyway: > > Does anyone have a quick explanation on why it is better (more > efficient?) to use 3 phases instead of two on industrial equipment? > > Thanks, > > Sean A Two-phase system, provided it is a balanced shift, will have instances where none of the phases supply current. In a 3-phase system there will be no instance where not at least two of the three will supply current. This means that for a three-phase system there will not be any 'dead' points. Greetz, Rudy Wieser

Russell was rumored to say: > WARNING - You can die if you try (but you may have to try hard). > > > Lower voltages (less than 50 volts) can't > > generate enough current through human skin to cause burns and stop > > your heart. Higher voltages (like 240) tend to knock you off or tend > > to make the muscles jerk so severely as to send the victim flying. I correct myself - Voltages less than 50 volts are not intrinsically safe, just less unsafe. > > While voltages under 50 volts are certainly safer and generally not > known to cause fatal shocks it IS possible if the voltage is upplied > correctly and under the right conditions. In medical applications such as open heart surgery they worry about MICROVOLTS. Extra effort is made to ground everything in the room back to a single point ground, and they have special ground monitors. > > Worst case I have heard of was an experiment long ago using convicts Fortunately most of those experiments have been outlawed. I keep hearing about old experiments on convicts, minorities, etc. that surface. Apparently it is very easy to convince oneself that an underclass of people are less than human in the name of science. > Yes, I've had hundreds if not thousands of shocks over the years and > handle wiring up to about 30 volts without a second thought - so far > I'm still alive. On a damp day 50 volts will prickle your hands if > you touch live terminals (telephone exchange distribution frame > during trainee engineering days.) Ringing voltage (70vac approx at > 16 Hz) gives a very nice kick. > We used to charge capacitors to 100 volts or so and hand them to another student. "Here- hold this." We'd also sneak up behind someone that was gingerly using a high voltage probe on a TV picture tube and goose them at the most inopportune moment. -- Lawrence Lile "An Engineer is simply a machine for turning coffee into assembler code." Download AutoCad blocks for electrical drafting at: http://home1.gte.net/llile/index.htm

Bill Cornutt wrote: > > A story that I heard while sitting on my father's knee > was that DC got a bad reputation after it was used on > a 'electric chair'. And the AC people said "That proves > DC kills!" I sure could be wrong, but I believe that it was Edison (who was promoting DC rather than Tesla's AC) who got the powers that be to use AC in the electric chair to show that Tesla's idea was the dangerous one. I also think that he went around eletrocuting sheep with AC -- sadistic spin doctor that he was. As I said, I could be wrong. Michael *************************************************************************When th e way of the Tao is forgotten, kindness and ethics must be taught. Men must learn to pretend to be wise and good. -- Lao Tzu *************************************************************************

On Thu, 23 Jul 1998, Lawrence Lile wrote: > In medical applications such as open heart surgery they worry about > MICROVOLTS. Extra effort is made to ground everything in the room > back to a single point ground, and they have special ground monitors. I was going to say that. Also, all electric/electronic equipment for Hospital use that involves any kind of wire to the patient must pass a test for leakage current several orders of magnitude below commercial equipment. > We used to charge capacitors to 100 volts or so and hand them to > another student. "Here- hold this." We'd also sneak up behind You are lucky with your 110 V ;) We had them charged to 310 V (220 pk). A 0.1 uF will pinch you badly and I guess 100 uF can make you hear angels singing. I should know as it was done to me once. Keeps the charge quite a while too. Peter

Mike Ghormley wrote: > Bill Cornutt wrote: > > > > A story that I heard while sitting on my father's knee > > was that DC got a bad reputation after it was used on > > a 'electric chair'. And the AC people said "That proves > > DC kills!" > > I sure could be wrong, but I believe that it was Edison (who was > promoting DC rather than Tesla's AC) who got the powers that be to use AC > in the electric chair to show that Tesla's idea was the dangerous one. I > also think that he went around eletrocuting sheep with AC -- sadistic > spin doctor that he was. > > As I said, I could be wrong. > > Michael > > *************************************************************************When the way of the Tao is forgotten, kindness and ethics must be taught. > Men must learn to pretend to be wise and good. -- Lao Tzu > ************************************************************************* I read a book about Tesla and Edison was totally against AC and used it to kil l animals in the street to show AC kills. one more tid bit.... Tesla worked for Edison when he first arrived in America

It also draws a hell of a lot of current at start up. At Texas A&M they have to give the power plant 2 days notice and then start the wind tunnel at 3:00 am. Gordon Gordon Couger TakeThisOuTgcougerspamrfdata.net 624 Cheyenne Stillwater, OK 74075 405 624-2855 GMT -6:00 {Quote hidden}>1) A balanced 3-phase system delivers constant instantaneous power. >Even though each phase delivers power in sinusoidal surges, >the sum of the three is a constant level. >Thus, no motor vibration or hum, reduced mechanical deterioration, etc. > >2) A balanced 3-phase system delivers the more power per conductor amp than >any other AC arrangement. >That means it's the most efficient way to provide electricity, in terms of >delivered watts per pound of copper. > >Peter F. Klammer / PKlammerEraseMERacom.com >Racom Systems, Inc. / 6080 Greenwood Plaza Blvd / Englewood CO 80111 >(303)773-7411 / FAX:(303)771-4708 > >> {Original Message removed}

Why dont they use 7200 volt motors for the wind tunnel? we use 350 and 600 horse electrics for our pumps at the water plant and we dont have to tell them when we start 6 pumps at one time. or does the wind tunnel use alot more horsepower? On Fri, 24 Jul 1998, Gordon Couger wrote: {Quote hidden}> It also draws a hell of a lot of current at start up. At Texas A&M they have > to give > the power plant 2 days notice and then start the wind tunnel at 3:00 am. > > Gordon > Gordon Couger RemoveMEgcougerEraseMEspam_OUTrfdata.net > 624 Cheyenne > Stillwater, OK 74075 > 405 624-2855 GMT -6:00 > > >1) A balanced 3-phase system delivers constant instantaneous power. > >Even though each phase delivers power in sinusoidal surges, > >the sum of the three is a constant level. > >Thus, no motor vibration or hum, reduced mechanical deterioration, etc. > > > >2) A balanced 3-phase system delivers the more power per conductor amp than > >any other AC arrangement. > >That means it's the most efficient way to provide electricity, in terms of > >delivered watts per pound of copper. > > > >Peter F. Klammer / @spam@PKlammerRemoveMEEraseMERacom.com > >Racom Systems, Inc. / 6080 Greenwood Plaza Blvd / Englewood CO 80111 > >(303)773-7411 / FAX:(303)771-4708 > > > >> {Original Message removed}

>Hi Andy, Paul, and others who responded, > > >Thanks for the explanation. I already understood that minimum current >causes minimum wire heating (i^2R), but I guess I still don't understand >why one couldn't just use a higher voltage instead of 3-phase. Using >multiple phases doesn't increase the voltage between phases much over the >single phase-to-ground voltage, does it? Becouse you increase a wires from 2 to 3 (*1.5) and increase the power in 3 times. (At the same U and I). Power wires are not cheap. >THe only outstanding reason that clearly makes sense to me is that the >phases deliver the AC peaks in rotational order for motors. Of couse. Async. morotors are very simple and cheap. ================================== Alex Torres, Kharkov, Ukraine (exUSSR) E-Mail: @spam@altorspam_OUT.....geocities.com 2:461/28 FidoNet Home Page: www.geocities.com/SiliconValley/Lab/6311 ICQ UIN 11083325

Pete Klammer wrote: > > 1) A balanced 3-phase system delivers constant instantaneous power. > Even though each phase delivers power in sinusoidal surges, > the sum of the three is a constant level. > Thus, no motor vibration or hum, reduced mechanical deterioration, etc. > > 2) A balanced 3-phase system delivers the more power per conductor amp than > any other AC arrangement. > That means it's the most efficient way to provide electricity, in terms of > delivered watts per pound of copper. Unless you count 5-phase, or 7-phase or ... Frank ------------------------------------------------------------------------ Frank A. Vorstenbosch <SPAM_ACCEPT="NONE"> Phone: 0181 - 636 3000 Electronics and Software Engineer Mobile: 0976 - 430 569 Eidos Technologies Ltd., Wimbledon, London Email: favspamBeGoneeidos.co.uk