As the owner of a VAX-11/780 I can confirm what Guy says about the 866 power controller. This is the only component that needs 3-phase power.
There is a small 3-phase transformer inside that provides 24V DC to the control circuitry. The power controller not only interfaces to the DEC power control bus to switch on other cabinets (with a delayed output) but also connects to airflow sensors above each blower. If the airflow fails then it cuts power to the system. The blowers themselves are all single phase. I converted my power controller to run on single phase by replacing the transformer (18VAC, 20VA). It's also important to note that the neutral wire from the line filter to the output rail is undersized for running the system on single phase. If the system were running on 3-phase then the neutral current would be minimal but running from single phase means ALL the current is going through neutral wire. I replaced this wire with one of a suitable rating. I am in the UK so the figures I give are for running a system which would normally be on 415V 3-phase from a 240V single phase supply. For 110V you can probably just double the current figures. I have the FP780 option as well as 2x DW780 and RH780 controllers. To power everything in the main cabinet takes about 16.5A. I run this all off a 20A circuit breaker (B-Curve RCBO). I have to turn on the H7100 power supplies one at a time. If I try to turn them all on at once the inrush will trip the breaker. There are two different versions on the H7100 in this system. The older version uses a 3 ohm resistor, which is shorted by a relay after power up, to limit the inrush. These have quite a high inrush current. The later version uses a thermistor in place of the resistor which greatly improves the situation. Once you have the main cabinet powered then to get a usable system you then need about another 4A to run the two BA11K Unibus boxes and whatever power is required for a disk drive. In my case that's usually an RA70 or RA72 so fairly minimal. I don't have any Massbus disks but I do have a TU77 connected to the system. The heating effect is noticeable after the system has been running for a while so you may also have to consider air conditioning power requirements. Matt
