The label on my central air conditioner looks a lot like this one (photo below). What do the two numbers (separated by a slash) mean for voltage and the three amperage ratings?

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The text Volts 208/230 Phase 1 means the device will run on either 208 volts or 230 volts (which is nominally 240 volts).

In the amps section, the separated numbers (which are the same) are the corresponding value for operation on 208 or 230 volts, respectively.

  • Just wondering: Where would one find 208 VAC? I'm used to 220-240 nominal, but... – keshlam Jul 18 '14 at 2:10
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    @keshlam: For light industrial, hotels, commercial areas, apartment buildings, or other users with big electric motors, it is common to get 3 phase 208 volt service. This has 3 "hot" wires, each 120 volts to neutral. Between any two of the "hot" wires there is 208 volts. See this. – wallyk Jul 18 '14 at 2:13
  • Ahhhh. Never dealt with three-phase, though I was aware it exists. The few places I've seen it in use, they were using motor-generator sets to get it from two-phase. – keshlam Jul 18 '14 at 2:15
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    @wallyk, this is not at all correct. "Phase 1" simply means single phase. 2-phase is extremely rare and not likely to be seen in the US, and 3-phase is just that, 3-phase. NONE of this suggest the need for a neutral. That would be conveyed in the voltage area. It would say something like 120/240, or 120/208. Since the label says single-phase 208/230 it means it requires two hots legs and NO neutral. A 3-phase A/C unit rated @ 230v would only require 3 conductors and a ground. – Speedy Petey Jul 18 '14 at 20:42
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    Who knows? Most likely an amateur that did not know conventional ways of wiring. I know lots of folks who think you need to run xx/3 cable for "220" because they don't know you can use xx/2 and re-mark the white. – Speedy Petey Jul 18 '14 at 21:15

To add to this answer, air conditioners, motors and welders follow different rules than what is considered conventional.

The MCA (minimum circuit ampacity) is what you size your wire by. The maximum/minimum fuse or breaker is what you can size your overcurrent (fuses or circuit breakers) by. So this unit, having a 19A MCA, can be wired with #12cu wire, and must be fused or breakered at 25 or 30A.

YES, I AM saying you can put #12 wire on a 30A breaker.

  • This only applies if the device is wired in. If you wire it with a plug you would have to use wire that is big enough for the breaker, and an appropriate outlet. – Brad Gilbert Jul 20 '14 at 23:15

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