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We're trying to setup rotary phase converter, and we're getting some differences in line voltage. The black reads 350 to ground while red and white read 120 to ground. This is all from a 220 input. Red to white reads at 240 volts. Any thoughts on the problem? I don't imagine this is normal.

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  • \$\begingroup\$ Why do you measure to ground? Don't you have neutral? \$\endgroup\$ – Gregory Kornblum Aug 8 '18 at 17:23
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    \$\begingroup\$ Make and model of the rotary phase converter? Photo of nameplate? Is the 220 V the single-phase input? (If so it's probably irrelevant as the output would be isolated.) Have you got a load on it? Is there a wiring diagram on the machine? Please put all the required information into your question. \$\endgroup\$ – Transistor Aug 8 '18 at 17:30
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    \$\begingroup\$ Seems a bit like a high-leg delta, but with some internal mis-wiring of the L1-L2 (red/white) phases. \$\endgroup\$ – brhans Aug 8 '18 at 17:45
  • \$\begingroup\$ Do red-black and white-black both read 240V? \$\endgroup\$ – brhans Aug 8 '18 at 18:01
  • \$\begingroup\$ We bought it with the CNC mills and it looks like a home brew type converter, so no name plate unfortunately. \$\endgroup\$ – zandermar18 Aug 8 '18 at 18:44
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If your rotary phase converter's output is wired for high-leg delta
enter image description here
then I'll present the following as a possibility.

When wired correctly, you'd expect to see something like this when measuring from each phase to neutral:
enter image description here and your measurements would be L1 & L2 = 120V, L3 = 208V.

However, if your phase converter is internally miswired like this:
enter image description here
then your result could look something like this instead:
enter image description here
and your measurements would be something like L1 & L2 = 120V, L3 = 317V.
So - not the 350V you're seeing, but maybe a possibility?

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  • \$\begingroup\$ That could be the case... So I would just have to rewire the coils to the legs? \$\endgroup\$ – zandermar18 Aug 8 '18 at 18:59
  • \$\begingroup\$ In theory - yes ... \$\endgroup\$ – brhans Aug 8 '18 at 19:27

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