Here's an interesting installation. This is a homeowner installed (he's an EE) balanced power system. It's based on a used 480v to 240vct dry transformer. It's running with a 240v primary to get a 120vct secondary. The center tap of the secondary is grounded yielding a 60-0-60v volt system. Of course this 10kva transformer is only good for 5kva in this configuration.
So the "neutral" although it's really no longer a neutral is at 60v above ground as is the hot. The secondary is protected through double pole breakers and there is a 60a SPA GFCI on the transformer secondary. As long as GFCI is used as well as double pole breakers, this system is apparently OK under a little referenced section of NEC??? Not sure if that applies to residential use however and this was not a permitted job. There are a few other requirements such as the outlets must only be in technical equipment areas and somehow labeled as non-standard power.
The owner here is using it to run his rather elaborate home theater system. He even has a computer floor in his equipment room! All those Ell's are poking into the rear of the main house panel on the other side of the wall.
This looks like a clean job, my guess is that it's here in So CA., (due to the garage vent and an all-in-one service). Article 647, though, which is a new one from the '02 Code, provides a limitation. 647.3(1) "The system is installed only in commercial or industrial occupancies". ...S
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