I am trying to find out some information about how 230 volt UPSes are wired up. In particular, I want to know how the output is wired with respect to the hot/neutral/ground wiring relationship. I am intending to get a "dual conversion continuous online" type of UPS, however, that may not actually happen, so I need to know this with respect to both types. I suspect the possibility these types may be different because the dual conversion type has more opportunity to isolate things.
What I am looking for is knowledgeable information, not conjecture. I am do plenty of conjecturing, so that is not in short supply.
I highly suspect, for safety and compliance reasons, the grounding wire is passed through solidly.
It's the 2 power wires that I want to know about. There are three different kinds of systems in the world:
- A specific wire is always the grounded neutral wire, with outlets and plugs polarized to ensure the correct connection. This can be seen in countries like UK, Australia.
- One of the wires is the grounded neutral wire, but outlets and plugs are not polarized, so plugging in can result in either wire being the grounded one. This can be seen in countries like Germany.
- Neither of the wires is grounded. Each wire is at half voltage relative to ground, in opposing polarity so the different between them is the full voltage. Outlets and plugs may or may not be polarized, but this would not matter. This can be seen in countries like USA for 2 wire 240 volt circuits (e.g. what you might plug a heavy duty air conditioner into).
I am wanting to operate the 230 volt UPS in the USA. What I want to be sure of is that there is no possibility of causing a short circuit through a backfeed, either in line interactive mode UPSes, or when a dual conversion UPS is in bypass mode.
I believe that would only be possible if one of the output wires is grounded while both are being passed through electrically. Since that would pose a hazard in the German wiring, I suspect it would not be the case. But I cannot rule out there may be another wiring strategy that would be safe in both UK and Germany, but not safe with the USA wiring.
A dual conversion UPS could be considered a "separate derived system" (in terms of electrical code), and probably wired as such. But how would it be grounded? I suspect one output wire is grounded and thus the other will be 230 volts relative to ground. If the switch that transfers to bypass mode is the "open transition" type, that should still be safe even with a USA power source, ehough it will result in a change in the voltages relative to ground when bypass in engaged.
There are UPSes designed for higher voltage specifically in the USA, but these tend to be much larger capacity (over 3000 VA), specified for 208 volts (instead of 240 volts), and usually are three phase type. What I need is 1500 to 2500 VA single phase.
I know most computer power supplies can be safely operated on 240 volts even with the USA style wiring. The power cutoff switch breaks both wires, and no assumption about which wire is made in any aspect of the power supply wiring. This is required in Germany due to the Schuko plug being able to rotate 180 degrees. I cannot recall ever seeing a computer power supply that cannot be operated on "220" (as labeled) either by means of a voltage change switch or autoranging.
Still, the big question is how the output from the UPS is wired to, or otherwise made relative to, ground. These units don't generally use isolation transformers, so whatever is done, it is done as part of, or in conjunction with, the output DC/AC conversion circuit.
Is there anyone using the "international" 230 volt UPSes on American style 240 volt (center tapped neutral) circuits?
Do you see or have any reason to anticipate any safety issues?