Conversations about your/my setup

Interesting.  In the UK we have 240V to houses, and schools etc have 3 phase 415Y/240V power.

Odd that your house has 240V, but your schools have 120V.  Must be one of those health and softy things.  In the school I worked at in the UK, they fitted very sensitive circuit breakers which tripped if you turned on too many computers at once.  Apparently the law states kids are sensitive to electricity and must be protected, but only in school and not at home.  I replaced the circuit breakers while they weren't looking.

In the school I worked at, an Irish subcontractor electrician managed to connect L1 and L2 to a set of outlets in a computer room instead of L1 and neutral.  Needless to say the 20 computers did not like a higher voltage and caused interesting fireworks and an awful stench in the middle of a class.  A £0.50 capacitor allowed me to repair the PSU in each one, but that's not what I told the insurance company.  The school got 20 new computers and we kept the "broken" ones.  However the projector I'd installed on the ceiling was the only thing to survive - the surge protector I'd fitted melted into a plastic blob and saved it.  That cost us £5 to replace!  I guess the the £250 projector we got off the insurance sort of covered it.

The Dell Precision PSU is 1100W at 100VAC - 180VAC and 1400W at 181VAC - 240VAC. I originally was planning to include a 3rd GPU which would have pushed it close to ~1400W. I did not end up going this route with the 3rd GPU but I might down the road. Now I have the ability to do so. I also want to introduce students to other hardware/platforms and I am not sure what that will look like, but having the extra overhead from the UPS/surge protection (which was a big expense) is nice. 

Nope.  Not if the rules are of any interest to you.  You could look up what applies in your specific case, but as a generalization authorized load is 80% of the breaker value, not 100%.

Of course if you are talking about what you might get away with for a while, as seems the theme of some comments here, that is a different matter.

Does anyone know why here in the USA we commonly speak of 220V, when in fact on the typical 2-phase layout it is just the sum of the two phases, which are quite commonly referred to as 120V, so the corresponding reference "ought" to be 240V?

I just got my main panel replaced to give proper sourcing to the charger for my new Tesla.  That charger routinely reports it measures 242 or 243V, which is a close match to the very low 120s I see when I meter my actual outlets.  I realize the power company would be well within rights supplying me much less, but I've not spotted that except the time we had a wide-area brownout about 20 years ago.  I actually saw 80V on my standard outlet that day.  The lights were dim.  Many computers died, including computers on popular home UPS systems.  A friend reported he was in a tire shop and watched as the shocked proprietor realized that expensive hydraulic equipment was giving up its last in a plume of smoke.

I don't ever recall any brownouts, but we do have what is politely referred to as 'direct load shedding' ie. they just cease supplying power to an area/district. This is typically during the afternoon of an extremely hot day, suggesting that air conditioning is collectively pushing the generators to their limit. At the control room this would be first noted as a persistent unintended voltage drop despite firing up more generating capacity. So rather than damage, possibly irreparably as you point out, equipment the line is dropped completely from some region.

{ It's worthwhile recalling that voltage is the chosen measure for 'electromotive force' or EMF and that something has to push the generators to rotate against resistance from the circuit(s) it is attached too. Often superheated steam is used in turbines. Matching generation to load requires continual attention. }

The quoted numerology of supplied voltage for alternating currents can depend upon which aspect of the cyclic current that is being referred to. If power into a resistive load is the measure then the RMS or 'root mean square' of a sine wave is used, that being about 0.7071 of the peak voltage excursion. Hence if one rectifies 240V AC ( RMS ) supply then you will get about 340 V DC  ( ie. 240/340 ~ 0.71 ) because +/- 340V are the extremes. For the RMS value between phases I'd have to do the math on the effective sine wave which is the difference of two sines, one offset by 120^o from the other .... but you get the idea.

{ Ideal inductors and capacitors do not take a nett amount from the circuit they are in. Nothing is ideal. Indeed your fluorescent lamp would not illuminate if there was no resistive aspect. }.

Cheers, Mike.

( edit ) ... as for plumes of smoke, the issue is frequently the start-up current to a compressor when the voltage is insufficient. So instead of some component rotating and expending mechanical power, the device's electric motor just sits there absorbing current resistively .... and I²R rules the day.