On 19/03/2011 11:49, Jochen Kunz wrote: I beg to differ. Y or D and voltage are two separate issues, and you probably need to get both right. Three-phase motors seldom bring out the star point even if they are Y connected, and will run from a Y or D supply of the right voltage impartially. Other stuff (basically, electronics) may be connected between two phases, or it may be connected between a phase and neutral. If the latter, it must by Y; otherwise it doesn't matter. The voltage must still be right either way. The electronics could even be connected between a phase and a "neutral" other than the star point (see below). So beware! Finally, I have come across kit (not a computer, I admit) that ran off 415V three phase, with the controls supplied by a little 415/110V transformer. In the UK, voltage is seldom an issue - almost all three-phase stuff is 400V or 415V, whether it's Y or D. Continental Europe goes in for 690V as well, and this is starting to appear over here for largish motors, which can be nasty. But I wouldn't expect to find that on anything as old or small as a 3880. In the US, all sorts of strange voltages and connections were used for three-phase supplies. Even the internet probably doesn't have a complete list! 208V was common, usually Y (so that phase to neutral would be 120V). I think 240V Delta was used, with a centre tap on one of the windings providing a neutral, so you got your 120V from either of the two phases on that winding. (I don't know whether it was normal to ground the neutral, but be aware that it was NOT the star point!) ISTR seeing 277V somewhere as well. This would be 160V phase to earth - I have no idea what, if anything, uses that! This means, inter alia, even a five-core mains cable could be a delta - three phases, centre tap of one winding, and ground - with no star point. My advice to you is find all the rating plates you can on the equipment, both outside and under the cover panels, and see if they agree on voltage and phasing. Rating plates on individual motors may help. Once you have done this, and wired up the appropriate supply, blip the power on very briefly to make sure the motors spin the right way. If they don't, swap two phases around. (Choose two phases symmetrically placed about the neutral if the neutral is not the star point.) Then, and only then, do a smoke test. I am not sure about equipment of that date, much less IBM equipment of that date, but I'd guess that undervoltage is less likely to be harmful than overvoltage. (Some switch mode power supplies may draw too much current if the voltage is low, and kill themselves that way.) So err on the side of lower voltage. HTH, Philip.

Basically, just about any configuration of wires that are sticking out of the wall can be hooked up to these controllers, and if they do not like what they are getting, they will not power up ("power check" in IBM talk). Just about everything is checked before any of the brains get any power. Not that one should be careless here, but IBM mainframe equipment does offer a bit of comfort when it comes to the smoke test. -- Will

Jochen Kunz wrote: If the power plug or cable has a neutral lead, you cannot assume that it doesn't need a neutral connection. For instance, a disk pack drive may use three-phase power for a motor, but you can't assume on that basis that a delta connection is suitable. It is not uncommon for there also to be a logic power supply with input wired from a phase to neutral. Note that neutral is NOT the same thing as ground. Neutral is a current-carrying lead. While neutral is connected to ground at one place (usually at the main breaker panel), at ANY other place in the local power network neutral may be at a significantly different potential (voltage) than ground, due to current causing resistive losses. Ground should never carry any significant current; if it does, there is a fault. The allowable current is varies by jurisdiction and type of equipment. In the US, for Class I (electrically insulated with protective earth ground) information technology equipment, the maximum ground leakage current is 0.75 mA for handheld devices, and 3.5 mA for other devices. Because the ground conductor is not supposed to carry any significant current, it should be at nearly the same potential (voltage) everywhere in the local power network. Not necessarily. Voltage requirements should be determined by the specifications for the equipment, which ideally are printed on it somewhere. Here in the US, the most common commercial three-phase power configurations are: * 120/208 wye - 120V RMS phase-to-neutral, 208V RMS phase-to-phase * 208 delta - 208V RMS phase-to-phase Notice that the phase-to-phase voltage is identical, so if something is marked as needing 208VAC 3-phase, that tells you NOTHING about whether it needs delta or wye. There are certainly other 3-phase voltages used in the US. Probably the next most common are 277/480 wye or 480 delta. Eric

Jochen Kunz wrote: Here in the US, I have yet to see a piece of equipment with a cable or plug with a neutral lead, that doesn't actually need it. That's why I suggested that if the cable or plug has a neutral lead, you should use three-phase-wye. I wouldn't necessarily even trust the schematics of a device. It's all too common for the published schematics to not actually match the equipment. Eric

I believe there is a 4 pin version of that connector. I am pretty sure I have a couple somwhere. Earth and 3 phases (Delta), of course. It's still red (incidating 415V or thereabouts). Whether it is commonly used is another matter... -tony

there are many, many, versions in serveal colours. This is what we used to call a 'BS4343' connecotr, and is sometimes known by the the trade name 'Commando' in the UK. Yellow 110V ones are common in 16A and 32A versions on industrial portable power tools over here (which as I mentioned a few months back are un off a 55-0-55V insolating transformer with the cnetre tap earthed). The blue 220V ones, in 16A and 32A versions are also quite common, I've also seen 63A and 125A ones. And red, 415V 3 phase ones are common in both 4 pin and 5 pin versions. There arel aosl other colours for 50V, etc, but those ae much less common. Sure. It is over here too. And if it's used, the neutral pin will be connected, so the wiring will be star (Wye). But I would not go so far as to claim that delta-connected 3 phasemains on the 4 pin socket never exists. -tony

Err, yes :-(. I haev seen some lethal wiring in my time that was installed by so-called 'professionals'. Not lethal, but when I was studying at Bristol, we moved a 3-phase pillar dril lfrom one lab to the next. Upon plugging it ino to the 3-phase socket in said lab, it ran backwards. I probalby violated $deity-knows-how-many rules by removign the cover of the motor switch box and swapping over 2 of the wires. However, quite why 2 sockets on opposite sides fo the same wall were wired with a differnet phase sequence is beyond me. -tony

On 2011 Mar 20, at 12:43 AM, Eric Smith wrote: I suspect our 120/240V (also 110V,115V,117V) split-phase distribution is a legacy of the "War of the Currents" between Tesla/Westinghouse and Edison. When Westinghouse entered they presumably had some interest in compatibility for end-users and existing loads with Edison's early distribution system, which was 3-wire and conceptually similar: +110, -110V & neutral.

Eric said: Oh, I see. Thanks, Eric! I was wondering what 277V was, but I had always assumed it was the line voltage, since that is what usually gets quoted. FWIW in rural parts of the UK, it is common to take just two phases of the HV (11kV) network on some spurs. You then get a single phase transformer from 11kV to 240V. For larger loads, 11kV/480V used to be common, with a centre tap to earth like the US 240V stuff, but this is dying out. Jochen said (in a post I didn't get): In the UK, single family houses are more common than on the continent. Except in rural areas (see above), three phases are run down the street, but each house gets a single phase supply from one phase and neutral. Engineers who have worked on LV installations tell me that no matter how carefully you specify the pattern of which house connects to which phase, the installers will connect to the phase that is easiest to get at... Even large electric cookers and water heaters are single phase here. Well, water heaters above 10kW usually need two phases, but those are rare. Blocks of flats, and my parents' house, have three-phase supplies, but each flat generally gets just one of the phases and the neutral, so that no-one is exposed to 415V. (My parents have electric storage heaters, and when these come on at night, the house draws 50A from each phase. But apart from the heaters, everything in the house is on the A phase, and everything in the annexe is on the B phase.) Philip.

All, On 21 March 2011 03:33, Tony Duell <ard at p850ug1.demon.co.uk> wrote: [3 phase connections and RCDs] Sorry. Should have replied to that thread but the thread went sideways. I am guessing the 100A phase to ground breaker that was being claimed and the RCD/ELCB/GFI 30mA breaker are two different safety systems designed to detect and break current for two different purposes. The transmission network (at least in Australia where I have experience with the transmission infrastructure) have a requirement to break the current on a phase to ground/earth fault. This is to protect primary plant and system stability more than than people coming in contact with the conductors. At 66kV and above on lines designed to handle 10's to 100's of MVA, people are generally considered as self clearing faults. I seem to recall what was quoted was likely to be more of the distribution system, which, at the current specified would be to protect the local distribution transformer against a phase to ground/earth or a phase to phase fault. It may also be the case that someone recalculated the numbers and realised that the circuit breakers may not be rated to break the fault current. Note that the current that the circuit breaker is required to break when a fault is present can be significantly larger than normal operating current. Without seeing the wiring diagram of the installation and the associated calculations, really it is all guesswork. Although, I too would be a little concerned if some equipment (as opposed to large plant) was leaking close to 100A of current to earth. That sort of fault current to a low impedance earth would result in something getting hot! The RCD/ELCB/GFI are designed to break the current before it has a change to interrupt the heartbeat, if someone forms a circuit between a suitable active conductor and earth. This is a much smaller current designed to protect installations where people are much more likely to come into contact with the current carrying conductors. Note that for the pedantic. I have tried to use ground and earth as appropriate. Where I am using ground/earth, it is where I would be expecting a three wire transmission system with the center of the Y winding connected to a large metal pole driven into the physical earth near the transformer. [chomp] Simon -- ------------------------------------------------------------------------ "Well, an engineer is not concerned with the truth; that is left to philosophers and theologians: the prime concern of an engineer is the utility of the final product." Lectures on the Electrical Properties of Materials, L.Solymar, D.Walsh

Doug Jackson wrote: That was rather... poetic. :-)

^^^^^^^^^^^^^^^^^^^^^^^^^ Isn't it more corret to say 'Otherwise the load is delta-connected and can be conneted ot a delta-connected supply. You could also conenct it to a star (Wye) supply of the appropriate phase to phase voltage by ignoring the neutral ocnnection of the supply'. Most computer systems that need 3 phase mains are star (Wye) connected, simply because you can connect single-phase loads (of which there are likely to be many) from one phase conductor to neutral. Murphy's law ensures that you will get this wrong the first time. If at all possible, make sure that whatever the motor is drivbing will not be damaged if it runs backwards 9remove drive belts, etc if necessary) and poer up briefly to see which way it turns. -tony