So when HP speaks of 1-phase and lists NA/JP for the models, they're really meaning split-phase, for the higher than 120VAC PDUs, correct?
NO!!!! Single-phase (or "1-phase") NEVER means the same thing as "split phase" Single-phase (at least here in North America) implies that one side ("Line") is "HOT" and the other side ("Neutral") is essentially at zero-potential (i.e. GROUND). In North America, the convention is that Neutral (white wire) is connected to Ground (green wire) at the breaker panel. And the equipment is designed on the assumption that Neutral will be effectively at zero volts. If you connect it to 120V you are just asking for trouble.
And split-phase is what we have coming into our house, not 1-phase, right? 120VAC - 0 - 120VAC.
Each side (120VAC to neutral/ground) is a "1-phase" circuit. What you have coming into your house (and virtually everyone's house in North America) are two "single-phase" circuits. You can get 240V from one "phase" to the other because of the North American convention established long before we were born. But those two sides are not REALLY "phases". Electricians call them "phases", but electronic engineers do NOT call them "phases" because they are not.
Appliances that are designed to operate on 240V in North America are designed to have the two 120V sides at 120V above ground. They are typically resistive heaters (water heaters, forced air furnaces, cook-stoves, ovens, etc.) And BOTH sides are well insulated and assumed to be always HOT.
But what you have is a piece of industrial equipment that was designed with the assumption that it would be connected to a source of GROUND_REFERENCED 240V. That is what THEY mean by "single-phase". Your PDU was designed on the assumption that the Neutral line will be essentially zero volts. Connecting it to 120V is a monumentally terrible idea. Before you identified what your mystery load was, we were assuming that it was some kind of gadget that might operate on "split-phase power. Perhaps a domestic welder or air-compressor, etc.
But you have a sophisticated piece of industrial equipment which has a bunch of sensitive and expensive loads (computers) connected to it. And that is a whole different ball-game.
I would rather try wiring it up myself, properly.
By operating a business in your home, you create a hugely gray area. Technically you should take out a permit and have an inspection. Else your can cancel your fire insurance because they won't pay off if you have done something like this and your house goes up in flames. Be sure and have a good off-site daily backup/archive scheme in operation.
Are you familiar with the brand name at all? Are they any good?
I would feel perfectly comfortable using that transformer if I were in the position of needing something like that. If you have any qualms, be sure and buy a transformer with proper approval stamps (UL, etc.) See Dave's recent video on this topic.
When I said Where I wouldn't be violating any codes, I was speaking strictly about the NEC, not the modifications (more like additions, from how I read the rules) that my local jurisdiction (Steuben County) can make to the NEC. Would this violate any of the NEC that all states must follow? If I cannot get passed that, there's no point going to my local governmental jurisdiction. As I understand it, they can add to the NEC, but they cannot remove stuff from the NEC. So if it fails the NEC right now, no matter where I live in the USA, no local governmental jurisdiction can modify the NEC in such a way where it'd pass.
That is why getting a plan from a licenced professional engineer will help you do something that is legal.
You won't find big industral transformers like that with "IP" ratings. They are designed for harsh, outdoor conditions. They are not designed to be impervious to water, they are designed to operate with rain-water washing through them. I can't imagine that there is any condition in your basement that would exceed what they would face every day outdoors. Of course, this assumes proper installation where the outer case is very well bonded go a good earth ground. Because the transformer is completely enclosed in a ground steel case, it should be safe from animals and children.
Finally, is 7.5KVA the correct rating for this unit?
Dunno? What is the power rating of the (unidentified) loads NOW? What are your expansion plans? If you are already starting out with 5KW load, then perhaps it might be wiser to get a 10KVA (or 15KVA) transformer.
Of course, this also begs the question how much power do you have coming into your house from the electric utility? Typical domestic service that I have seen is 240V @ 200A which is 48KVA (minus what the rest of your house uses). Do you have/need air-conditioning for all this? Remember that when it comes down to it, a computer is just a really expensive heater. If your computer uses 1000W, then you need enough air conditioning for a 1000W heat source. So a rule of thumb is to plan on enough power to keep everything cool as well as powering it.
Because of the money we have invested in equipment at this point in time, I do not feel comfortable discussing publically what the loads are, however, if you would like to know, I would more than happy to PM you. I would love it if one of our servers drew 1,000 watt! That'd be nice. As for the cooling, eventually we will get central air, but right now, being in the basement, we've kinda got lucky. Throughout the year, it seems to maintain an almost stable temperature and is cool. We have sensors for the rack, that monitor humidity, temperature, water / moisture, etc.
I am glad that you explained the IP rating a bit more in detail. Going off that paper, it's easy for me to not fully understand how safe it is. By reading the rating of IP14, I thought, oh no! This isn't what I want at all! But after what you said, it seems IP14 is perfect.
I'm still a bit confused about the phases here. I understand how the 240VAC works in the US. 120VAC to neutral, 120VAC to neutral, 240VAC going from hot to hot. I understand the breaker panel, I've studied it and the various names. I know the ground buss-bar and neutral buss-bar's are connected with a jumper wire usually. I know there's a hot buss bar where every other connector runs off the other incoming main line.
For example, the first single pole breaker, #1, runs off the first of the two incoming main 120VAC hot lines. #3 (directly below it), runs off the second of the two incoming main 120VAC lines. #5 runs off the first, etc. This is why when we install double-pole breakers, we can get 240VAC from hot to hot, instead of just 120VAC.
If I were to somehow attempt to create my own 240VAC source by using single pole breakers #1 and #2, it shouldn't provide 240VAC, from my understanding (I've never attempted), but should provide 120VAC, because they're on the same "phase".
So, if what we have is called 1-phase, but not by electrical engineers, what is it called by electrical engineers, and what is split-phase? I thought split phase was the whole 120VAC - Neutral (or ground) - 120VAC, giving us 240VAC....
I thought split-phase was where the hot was split between two wires, each 180 degrees out of phase. When one was at 120VAC, the other was at -120VAC, giving us 240VAC.
Also, in the first post, I believe, I did mention that it was a PDU for my server rack, because I realize even the name PDU could mean multiple things, and it's important that you guys knew I was referring to a power distribution unit for a rack, holding expensive computer equipment.
Finally, because we are running a business, have a daughter, living in the city, etc, we will always follow the law, and get the proper permit, after drawing up our design, and have it inspected. In the country, where we used to live, when I ran the 240VAC to my BGA rework station, we had tried, but the city inspector didn't really care about the country, which we thought was odd. Technically, we were living in the Town of Country, not the City, but they said generally, in the country, you just wire it up or hire someone to wire it up. They wouldn't actually come up to inspect my work. I thought that was horrible and should have been reported.
I still want to wire the transformer myself. I want to learn this stuff and I feel that I can do it, although I might need a little guidance. I don't expect anyone to do my homework for me, just maybe double check my design before I take it to the city, that's what I'm hoping for.