Three phase and IBM

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