Closed Delta 120/240V 3-phase service

On Thu, 14 Feb 2008 19:38:18 +0000 (UTC) Michael Moroney
| snipped-for-privacy@ipal.net writes: | |>On Wed, 13 Feb 2008 16:48:16 +0000 (UTC) Michael Moroney | |>| |>| I would assume no effect, as long as the insulation was rated for 208VAC |>| to ground vs. 120VAC to ground, and you don't overload the possibly small |>| high leg transformer. The insulation won't be an issue for anything |>| designed for European use where either leg may be hot, since either leg |>| must handle 240V. One overload problem is when something is connected |>| across the missing leg of an open delta system. The transformers have to |>| deal with a higher VA per delivered watt, plus more copper losses. |>| Combine this with a small high leg transformer and you may see voltage |>| sag. | |>Would a computer overload it? | | What do you mean by "computer"? A PC or a big-assed old mainframe? | I seriously doubt a PC with a 400W power supply will overload a high leg | transformer of a few kVA.
PC. I didn't think so.
The old mainframe might want three phase (to run its 400 Hz motor-gen set).

snipped-for-privacy@ipal.net wrote:
  Quoted Text Here  
They could also be an open delta, where most of the load is single-phase. The big one is center tapped, and handles all of the 120V loads. The small one only handles three-phase loads, perhaps a roof top A/C unit. I saw this exact setup at a factory that was having problems with one of their VFD's. The voltage imbalance was terrible. We brought in a genset and proved that the power system was to blame. When the system was originally installed, the building was a warehouse with only an A/C unit on the three-phase, so it worked great. Nobody thought to check it when the manufacturing equipment moved in with heavy three-phase loads.