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We have a 220 outlet for our A/C. We are shopping for a new unit and all I am see is 230 volts on the units. Will we have to rewire with a new outlet for a new A/C?

  • Rule of thumb for home appliances: 220, 230, 240, it's all close enough not to worry about the difference. There's a good chance the actual voltage on your outlet is somewhere in between and it's even possible the voltage is even lower than 220 (say, 218). – Mast Jun 19 at 6:18
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Two issues:

  1. In the world of electrical power devices, there is a "Distribution Voltage" that your utility is providing to you, and there is a "Utilization Voltage" that your devices are designed to work on. They are not the same values, because it is EXPECTED that there will be a "voltage drop" that takes place between the utility transformer and the point at which the device connects due to the resistance of the wire between them. Distribution voltages are required to be +-5% maximum deviation, Utilization Voltages are supposed to be +-10% minimum acceptable.
  2. Distribution voltage levels have changed over the years. Here in the US (we don't know where you are), 220V was an old original standard going back to the 1920s. Some time around the 1930s, as part of one of Roosevelt's "New Deal" programs called the "REA" (Rural Electrification Act), power lines were run out to farms and small communities all across the country. So to avoid having the REA workers have to carry different products for different utility voltages, a standard was established that has become codified as the ANSI (American National Standards Institute) Distribution Voltages that power utilities are SUPPOSED to adhere to. So for residential single phase distribution, the official voltage is actually 240VAC. But because old habits die hard, and because SOME utilities never actually changed, "220V" is a common term still used all over the place. It's actually somewhat rare for it to actually BE 220V. Generically, it's all referred to as being the "nominal" voltage; 220, 230, 240 all being relatively close enough.

So partially because of this, the unofficial "Utilization Voltage" level has been 230V for decades, but the tolerance is +-10%, meaning the devices are supposed to be designed to accept anything from 207V to 253V. In reality because some commercial and apartment complexes will use 208V 3 phase distribution, and you want to be able to accept 90% of 208V, the equipment manufacturers often actually make their products suitable for -15% from 230V (195V).

RARELY, something is either old, or made somewhere where they don't follow industry norms (or don't understand, or don't care) and they made it so that it STRICTLY requires a very narrow input voltage. So bottom line you should check. But if it is something like a dryer or an oven outlet, it should be perfectly fine.

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    220 wasn't even the original voltage. It was 200, or to be more precise 100/100 split phase, and 500V for streetcars. It was also DC. A bump was made to 105V etc. in coordination with light bulb makers. Then another bump to 110/220/550, and then, power companies yielded to the inevitable and switched to AC. RMS AC so you could keep using the same light bulbs. It got widely sold as 110/220, and that stuck like Xerox. Subsequently there were bumps to 115 and 120 today, with streetcars at 600 but they remain DC. – Harper Jun 18 at 5:29
  • From my understanding the voltage has risen to reduce the size of electrical wire. An increase in volts decreases Amps. – Alk Jun 18 at 12:01
  • @Alk for non-ohmic loads it does. So the power supplies inside computers etc. Incandescent lights are ohmic: V=IR so will draw more current at higher voltages (and get hotter, and die sooner). – Chris H Jun 18 at 12:32
  • @ChrisH -- that's true for the load, but not for the transmission line, which is a small part of the overall load. The higher the voltage on the transmission line, the lower the current for a given amount of power. So higher voltage means less current, hence, smaller wires. – Pete Becker Jun 18 at 13:56
  • @PeteBecker yes, I realise that. I deliberately stuck to the consumer end as Alk's comment was about the voltage delivered to the consumer, not the transmission line. They can be set almost independently as step-down transformers have variable taps; in fact lowering the voltage to the consumer, while keeping it within spec, is used to reduce load on the grid, as resistive loads account for rather a lot – Chris H Jun 18 at 14:45
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220/230/240 are the same thing, really

US single phase line-to-line mains voltage is interchangeably referred to as 220V, 230V, and 240V. This is because it started off as 220V, but was raised incrementally over time to deal with increasing demands on the grid; right now, it's said to be 240V at the service entrance, but 230V at loads to account for voltage drops in building wiring.

(There are several three-phase systems in the US, with various voltages involved, but they are beyond the scope of this answer.)

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    Am confused, I thought the US had 110V at 60Hz? – Michael Jun 18 at 8:31
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    The US mostly uses a split phase system, so the line to line voltage is twice the line to Neutral voltage. – Peter Green Jun 18 at 8:49
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    @Michael - YEARS ago it was 110 for regular, lower power appliances, and 220 for higher power appliances. The confusion remains, even with people who aren’t old enough to have ever worked with 110 volts. And to Peter’s point, residential power is a split (“center-tapped”) single phase system where the secondary of the transformer is 240 volts, line to line, but a “tap” is put in the middle of the secondary so that two 120 volt outputs result. For commercial buildings, it is typically a 3-phase system with 120 volts line to “middle” and 208 volts line-to-line. Confused more? – Julie in Austin Jun 18 at 11:13
  • @Michael: It's 120V, but 240V is also used in homes, mainly for ranges (stoves) and dryers – BlueRaja - Danny Pflughoeft Jun 18 at 17:28
  • @Julie in Austin: Live-to-live is 240V (obviously, when live to center tap is each 120V). 208V is center tap to high leg live in that triangle. upload.wikimedia.org/wikipedia/commons/c/cf/High_leg_delta.svg Using the 208V wiring for "230V" appliances has the advantage of a more even power distribution between the there live wires, while retaining a common neutral. – Janka Jun 19 at 3:03
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Just for interest, here in the UK the reverse happened. Our national supply used to be nominally 240V, but at some point (perhaps for inter-operability with the EU) it was dropped to 230V. In any case it's +/- 10%, so 230V might be 253V worst case.

The safety specifications will include a much greater margin of error that the hardware must safely handle for short periods of time before fuses or circuit breakers can do their thing. I was once in a building when a substation blew up, and for a brief period of time one of the phases dropped out and the other two went seriously over-voltage before darkness descended. I was pleasantly surprised how little needed repair when the power came back on.

Old-fashioned electric motors will compensate for a lower voltage by drawing more current thereby maintaining an almost constant output power. Modern a/c motors have complex electronic control of the actual output power (i.e. the amount of cooling or heat-pumped heating that is supplied), which is more efficient than just turning on and off at fixed thermostat points.

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In Europe, there were various standards requiring either 220 V or 240 V in various places. Britain even had 250 V in some areas. This was all standardized to 230 V in the EU and surrounding areas (the European Network of Transmission System Operators) so they could be interconnected. Not much actually changed, as the voltages are all within acceptable tolerances of each other.

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