This has turned out to be quite a detailed thread!!!
I have some comments regarding the items covered so far.
Per the UPS equipment specified by the OP "pdh":
After reviewing the Products' Documentation, I am unsure if either of the Two Models will have a Grounded Output - while the Output is running Isolated via the Inverter / UPS Transformer (in Normal Mode or in Bypass Mode).
OP indicates that, after contacting the Tech. staff for verification of a Grounded system, it appears that the single output voltage system does not have a Grounded System Conductor.
This would be the UPS with an output of 208V 1 PH. 2 Wire (with EGC).
The above UPS _MAY_ have a Center Tap on the Secondary, and _MAY_ be Grounded via that Center Tap.
Results would indicate 104 VAC L-G from either of the 208 VAC lines, and would deliver a Grounded system without a Grounded System Conductor.
It could be possible that either of these UPS units do not have the Secondary Winding bonded to Ground. Only a Schematic or Field Test could verify.
When the UPS is set in Bypass Mode, the Output is directly connected to the Circuit driving the UPS Input - and the Isolated System is not connected.
As to using an Ungrounded System (setting up an Ungrounded System)...
Let us first off designate what will be considered an Ungrounded System for this scenario.
My description of an Ungrounded System is:
*** A Power System of "X" Volts AC, which does not have a DIRECT connection to a Grounding Electrode System, yet will have Metallic Enclosures Bonded to a Grounding Electrode System, along with a Measurable Voltage-To-Ground across a given Impedance ***
The Voltage-To-Ground on the above described Ungrounded System will vary, according to the Impedance between a given System Conductor and the Grounding Electrode System.
The higher an Impedance value is, the higher the Voltage between the Two points will be.
My description of a Grounded AC System, which does not use a System Grounded Conductor would be:
*** An AC System, which has a DIRECT connection to a Grounding Electrode System, yet does not utilize a System Grounded Conductor with the normal "Output" Circuitry from the Secondary Winding(s) of the Transformer, but does utilize Equipment Grounding Conductors which are Bonded to both the System and the Grounding Electrode System ***
In the case of the above System, the Center Tap of the Secondary Winding (or one Secondary Winding), will be Bonded to the Grounding Electrode System, without deriving a Grounded System Conductor from that Tap point.
All EGCs will be bonded to that Center Tap, as well as the GES.
The 60/120V 1 Phase 2 Wire System is one example.
The issues involved with high L-G Voltages experienced on an Ungrounded System may rapidly damage SPDs, as well as line Filters at the input of a SMPS.
The typical MOV would be subject to high L-G Voltages, corresponding to the Impedance of the device.
To reduce the issues connected to using an Ungrounded System - in addition to using an AC Circuit without a Grounded Conductor, the "Center Tapped" System above would be a good choice.
I agree with the Fiber Backbone idea between two or more Buildings, and/or for long distances.
Even with all Electrodes connected together, there will still be a difference in potential between the two Electrodes.
Circulating Currents are likely to flow on Conductors bonded to the GES.
Scott
