I had an old flat some years back which had been converted from 220 V phase-phase to 220V phase - neutral. Strange looking setup with two main switches, one no longer in use and all fuses in pairs, with one unused in each pair. Sure enough, when I put the voltmeter across the main fuse and its abandoned twin, I measured 400V. I presume the wires had simply been moved in the fuse box when the utility changed to voltage from 12/220 to 220/380V.
