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I have a project where the existing pad mounted utility transformer is configured as delta-delta. The utility company says it is an un-grounded delta secondary at 480V/3-phase/3-wire system. I asked them to take voltage readings between phase-phase and phase-ground just to make sure it is an...
This is mainly to cater for voltage drop. 480 volts is the system voltage. 460 volts is the rated voltage of your equipment. 460 volt rated equipment is always used on a 480 volt system to account for voltage drop due to starting or line losses. In any event, you are fine.
This serves two purposes; it allows for voltage drop at the motor terminals and it falls within the NEMA MG-1 tolerance specifications (+- 10%) for the legacy systems that are still out there. For example, 440 +10% is 484, 480 - 10% is 432 so 460 falls smack dab in the middle and everyone is happy.
A single 480-volt phase wire and a neutral would give you 277-volts unless it is a corner grounded system, just as on a 120/240 volt system one phase conductor and the neutral give you 120 volts. With a 480 volt single phase you would need two hot conductors (ungrounded conductors) and a grounding conductor - no neutral required.
Say you have a 480/277 Volt generator. Would there be any problem leaving the neutral off of the generator and just running 3 conductor 350 MCM to the transfer switch? The 3 conductor 350 MCM cables from the transfer switch feeding the MCC have no neutral and don't need or have any 277V loads, nor is there any plans for 277V loads.
Take a closer look- this is a delta not a Y. Same thing as a 120/240 3 phase 4 wire service except double the voltage. Instead of a high leg of 208 volt you have a high leg of 416 volt. Used to be very common in some areas for things like oil wells, irrigation pumps, etc.
480 volt three phase down to 380 volt three phase. Transformers of this rating usually have a long lead time. Would there be anything wrong with using a three phase transformer with a 600 volt primary and a 480 volt secondary? With 480 on the primary, the secondary should produce 384 volts. Would the lower excitation
A 480 Volt to 120 Volt is a natural. Transforming fro 415 Volts to 480 Volts with an open delta requires a non-standard voltage. Some of the major plants around Fort Mac. are 600 Volts, some are 480 Volts.
One is the voltage to ground; the other is the nature of the wall (or other surface) on the opposite side of the "working clearance" from the front of the panel. So if this is a 480/277 volt panel (or a 480 volt delta, either way), and if the opposite surface is grounded (very high probability), then the minimum working clearance is 3.5 feet.
So with my example of 1.2kVA @ 240 volts it draws 50 amps. It will draw 25 amps @ 480 volts. The ability to start some motors could complicate selection some but the basics are VA in is equal to VA out, losses in conversion are typically low enough they can be disregarded.