saaf@joker.optics.rochester.edu (Lennart Saaf) (09/19/89)
> From: saaf@joker.optics.rochester.edu (Lenny Saaf) > Date: 12 Sep 89 21:59:29 > Subject: 110/220 v question > > I know that in this country most homes receive 2 110 volt AC lines > with different phase and a common line, allowing us to get 110 off > either side or 220 across both. I know this is called (some number) > phase, but will refrain from guessing to avoid flames. Is this wiring > scheme also used in 220 volt land? That is, can homes access 440 > volts from their service drop? I will summarize the responses. Below is a summary of responses I received. Many thanks to all who wrote! - Len ******************************************************************************* From: Ken Yap <ken@cs.rochester.edu> No, not universally. Many 240V places use a more efficient scheme called three phase where the feed is three wires 60 degrees apart in phase. Each phase is a 240V circuit. Between the phases the voltages measures 415V (240 * sqrt(3)). There is a common return for the three phases but with proper balancing the current in this can be kept small. From: Roy Smith <roy@phri.nyu.edu> I have always heard it referred to as "split phase". Note that electricians are famous for doing all sorts of strange stuff. Often, 208 (i.e. phase to phase on a normal 120 phase-to-neutral system) and 240 (i.e. both sides of a +/-120 "split phase" system) are interchanged. Most equipment can deal with the 15% off-voltage line without too much of a problem. From: prv@philabs.Philips.Com (Paul Veldman) In all western European countries I know of, the distribution of electric power to domestic end-users is done by a three phase 380V delta/ 220V Y connection scheme. "Normal" (relatively low power) end-users simply get a single phase (R or S or T to N) connection. High power end-users (e.g. electrical cooking) can request three phase 380 V delta outlets. So, combination of "phases" from different outlets will normally only give you 220 V or 0 V. If the installation is three phase fed AND different groups of 220 V outlets are connected to different phases (very rare!), you can get 0 V, 220 V or 380 V. Never 440 V. For England, with its 240 V mains voltage, you should read 240 V and 415 V for 220 V and 380 V respectively. The N (Neutral) is connected to ground at the distribution transformer, not at the end-user. It is therefore not uncommon for the N to show a substantial voltage to end-user's ground node, up to 60 V. Because of this, the Neutral has to be treated in the same way as the Phase wire. (Connecting the case of an apparatus to the Neutral terminal, as in older US equipment, is therefore strictly forbidden). The most important reason some countries still use polarized plugs/outlets lies in the fact that some countries require that switching is done in the phase-wire. From: witold@june.cs.washington.edu (Witold Paluszynski) No, at least in (continental) Europe the power is 3-phase so the voltage between any two phases is about 380 V. Typically, high powered appliances are built as 3-phase devices so as to avoid unbalanced loads. From: wombat!george (George Scolaro) In Australia we get 3 phase power as an option to a residential house. Normal power is nominal 240V single phase. 3 phase looks like: 1st phase 2nd phase \ / \ / \/ Neutral | | | 3rd phase ie total of 4 wires. Note that neutral is a very thin wire (in comparison to the other 3) and carries the (hopefully) zero current back to the transformer. Voltage from Neutral to each phase is 240 Volts, this is called single phase, most appliances run on this. Voltage from phase to phase is 440 volts (nominal), ie 240 x sin(60) x 2 volts. (via phasor diagram) The single phase power (one of the three phases to neutral) is chosen per group of houses such that each phase is equally (hopefully) loaded, to try an zero the neutral current. Of course this means a bang if you happen to try and run a wire from active of one house to the active of another house if they are on a different phase! All appliances either are 240 volts single phase, or 440v 3 phase. 3 phase is typically only used for large motors, eg pumps etc and few houses have 3 phase service. It costs more, since you get 3 power meters on your wall, and you get charged rent on each+cost of power. From: vermilye@oswego.oswego.edu (Jon R. Vermilye) The correct description for the standard service available for most homes in the US is 120v/240v 1 phase. It is derived from a center tapped transformer with the center tap grounded. Across either of the "Hots" and the center tap provides 120V & Across the two "Hots" is 240V. The most popular multi phase service available is 3 phase. This is produced by three different windings in the generator spaced 120 degrees apart, producing 3 phases each 120 degrees from each other. This is usually available as a Delta Connection where each winding is connected to the next, head to toe, or as a Wye where the same end of each phase is connected to a common point (which is usually grounded). The Wye is more useful for general lighting, etc since it can provide dual voltages (120 & 208V) while the Delta is most often used for motors, heaters, etc, and is usually available at only one voltage. From: al%computer-science.strathclyde.ac.uk@NSFNET-RELAY.AC.UK Electricity Boards here distribute a 3 phase supply. That is 240 per phase in either 3 or 4 wire configurations. The supply to consumers it always 4 wire. Anyway, doemstic consumers are given a feed of a single phase, hence they get one live (hot) wire, one neutral and one earth. Modern PME (Protective Multiple Earthing) with connect the earth and neutral immediately outside the consumer's premises. Industrial consumers and large users are suppled with a 3 phase supply at any of a range of voltages depending on needs. A typical large consumer with no special needs will receive a 3 phase 240 volt per phase supply, giving 415 volts accross phases. The consumer will then distribute the phases around the premises in such a way that the overall neutral current should be near zero. Wiring regulations prohibit the use of sockets carrying different phases to be closer than 4m, there by avoiding (or at least trying to avoid) the possibility of a 415 volt electric shock when someone touches two ajacent faulty appliances on different phases. From: mbe@dde.dk Here in Denmark (and I guess in most other European countries) the power is distributed with 3 220 volt AC lines and a common line. This is called 3 phase. There is 120 degrees between each phase. This way homes (normally) can choose between 1 x 220 volt AC and 3 x 380 volt AC. The reason for 380 volt is that the power is taken directly from the 3 'hot' lines with (ideally) no current in the common line. Remember the phase angle (120 degrees) between each 'hot' line. X / . \ / . \ / 220 \ / . \ 380 . 380 / .C. \ / . . \ / 220 220 \ / . . \ Y ------- 380 ------- Z This figure is a illustration on how the voltages is distributed between the lines. X, Z and Y means the 3 'hot' lines and C is the common line. As you can see, you can get 1 x 220/380 volt, 2 x 220/380 volt and 3 x 220/380 volt. From: jano@chalmers.se (Jan Norden IMT) Here in Sweden we use 220/380v three phase, that is you can either get 220v between phase and ground, or 380 between two phases. Radiators, ovens and stoves will in general have 380v elements to even out the load between the phases. From: otto@jyu.fi (Otto J. Makela) Well, over here the 3-phase difference is 380V and against common you get 220V. So, it's different. I wasn't aware you could get 220V in the US ? From: BHB3@PSUVM.BITNET Well a know common househould service is called "single phase" in references to electric motors. From: hakanl@loglule.se (H}kan Lennest}l) Here in the nordic countrys we have a three-phase system. All households are connected with three live "phase" wires plus one "zero" and possibly one ground. You obtain 220 volt between "zero" and one of the phases. And 380 volt between two of the phases. I am no expert on this, but I think that this is the general idea. From: pcf@galadriel.bt.co.uk (Pete French) British mains is 3-phase, but a house only noramlly gets a single phase supply. larger buildings may have 2 or 3 phases comming into them. >From these you can access 415 volts. These are used for machinery in places lie factories etc... -- ------------------------------------------------------------------------ | Len Saaf, The Institute of Optics, Univ. of Rochester, Rochester, NY | | Internet: saaf@joker.optics.rochester.edu Bitnet: SAAF@UOROPT | ------------------------------------------------------------------------
michael@xanadu.COM (Michael McClary) (09/21/89)
Saw an odd hookup once. (Skating rink kinda northward in
Michigan, used a LOT of electric heat - back when juice was
cheap.) Was like this:
Z
/ \
/ \
/ \
/ \
/ \
X-----N-----Y
Standard 110/220 at X/N/Y, and 3-phase 220 at X/Z/Y. This let
them feed three times as many heaters for 50% more copper, using
standard 220v heaters. The heaters didn't care if N(neutral)
(= ground) wasn't centered.