convert outlet from 230V to 115V

[markmikko]

I purchased a thru-the-wall A/C unit that runs 115V to replace an out A/C and didn't realized the old ran on 230V. Is there an easy way to convert the 230V outlet to 115V?

[DanG]

I assume this a US question.

Yes and no. The very fact that you needed to ask sounds like this might be a bit too technical for you.

220 volts does not require a neutral. 110 absolutely must have. Both should have a ground.

How many wires and what colors in your receptacle? Let's assume you have red/black/white/green. Use a volt tester and check the voltages:

between red and black you should get 220 between red and white you should get 110 between black and white you should get 110 between white and green you should get none.

If all this is true, replace the existing receptacle using either blk or red on the brass screw / white on the silver screw / green on the green screw / cap off the unused blk or red (or better, take it off at the breaker).

If this is not what you have, hire an electrician.

[Nate Nagel]

sure, replace the double pole breaker in your breaker box with a corresponding amp rating single pole breaker. (never go bigger unless you are sure that the wire gauge is acceptable to use with the breaker you are proposing to use) Connect the black wire to the new breaker, connect the white wire to the neutral bus. Replace the receptacle with a 115V receptacle. Cover the hole in your breaker panel's cover. Et voila.

nate

[Doug Miller]

Probably, but that depends partly on the amperage rating of the existing circuit, and that of the new A/C unit. If the new unit is rated at higher amperage than the existing circuit (e.g. you have a 15A circuit, and a 17A air conditioner), you'll need to replace everything.

BTW -- it's 120 / 240 now. Hasn't been 115 / 230 for a long, long time.

Assuming that the amperage ratings match up, here's how you can go about it:

First, obtain a 120V receptacle of the proper rating. You might need a 20A receptacle, depending on what the new A/C requires.

Next, test the outlet with a circuit tester or voltmeter to verify that it's live. Turn off the circuit breaker and test it again, to verify that it's dead. (This protects you against the possibility that a faulty tester is incorrectly showing a live circuit to be dead.)

Then remove the existing receptacle from the box in the wall -- DON'T disconnect any wires from it yet -- and look at what's connected to it, and what other wires may be present in the box.

Most likely, there will be three wires connected to the receptacle (black, white, and bare), and no other wires present. If not, STOP NOW, and post here again, describing what you *do* have -- and ignore the rest of my reply.

Remove all three wires from the existing 240V receptacle, and connect them to the new 120V receptacle as follows:

- black to the brass-colored screw

- white to the silver-colored screw

- bare to the green screw and install the receptacle in the box in the wall.

Take the cover off the circuit breaker panel. Disconnect the white wire from the circuit breaker for this circuit (leaving the black wire in place). Connect the white wire to the neutral bus bar in the breaker panel. (This is a long bar with many screw terminals, that already has numerous white wires connected to it.)

Turn the breaker back on, and check the new receptacle with one of those plug-in circuit testers that shows you whether it's wired correctly. Or test with a voltmeter: you should see 120V between hot and neutral, 120V between hot and ground, and 0V between neutral and ground.

If everything tests correctly, put a cover plate on the receptacle, plug in your A/C, and enjoy the cool.

[mm]

If I recall correctly, 220v ACs are more efficient than 110. CAn you return the one you have and get one that works on 220/30/40.

(Doug, I live in the 110/220 world and don't plan to move until I reach the Next World.)

[barry]

IIRC, if you calculate the actual rms voltage, a "110" or "120" volt line is actually 117v. Of course this is nominal, since it excludes noise and IR drops.

So, yer both right.

J

[mm]

Thank you. :)

[Mark Lloyd]

How would you get that?

BTW, my outlets usually supply exactly 120V RMS.

[Chris Lewis]

According to Mark Lloyd :

Unloaded.

Power specifications take into account permissible voltage drop under load. The permissible voltage drop includes the +/- 5% tolerance or so permitted at your service panel's 120/240V and the 5% or so voltage drop permitted over the house wiring and supply cords.

Which basically means that house power is allowed to be (by code and regulation) anywhere between about 110V and 130V.

In other words, some people call it 110V, others call it 120V, and some people pick numbers in between. And of course, most volt meters aren't very good at this accuracy on AC house power either.

[Mark Lloyd]

OK, about the voltage drop and permissible voltage ranges. However that doesn't seem to explain how you got that specific number (117). Are you measuring peak voltage somewhere and calculating from that?

The outlets in my house are normally supplying 120V with no load (other than the kill-a-watt meter). Where is the 117V in that?

BTW, The voltage numbers I remember hearing about are 110V, 115V,

117V, 118V, 120V, 120V and 220V, 230V, 235V, 240V.

[M Q]

...

...

Can you tell me which NEC sections say that?

[Chris Lewis]

According to Mark Lloyd :

Stick a toaster on the line, and you'll see something _other_ than 120V ;-)

[Our house power, according to my reasonably accurate meter, is 127V. Which makes sense where we live.]

I seem to recall somewhere seeing that 117V is the exact calculated RMS value from some specific regulatory "peak" _nominal_ voltage.

The point being that because of resistive losses and power station management, it is _allowed_ (by code and power regulations) to vary a fair bit. This means in practise there's a considerable variation in the voltage present on a given outlet, moreso when you figure that many voltmeters aren't very accurate on AC RMS voltages either.

Think about them as being dialects of "power speak", all meaning the same thing in the end.

One of the reasons for that is pragmatic - Eg: motor HP and current draw are often specified at the lower end of the permitted range, because that's worst-case for heat generation/ultimate limits on the device.

Other reasons are simply habit - what grandpop used to call it.

Like, you say ToMAYto, and I say ToMAWto, but they're both red fruit ;-)

[Mark Lloyd]

Voltage drop with load. I've made different tests. Usually with that meter in an outlet, then plugging in a hair dryer and seeing the voltage change. The amount of voltage drop would vary greatly (usually in the 1V-5V range) depending on things like amount of load and distance from panel.

I was wondering why the SPECIFIC value of 117V was mentioned in an earlier post.

In college I was taught that peak voltage = 1.414 * RMS voltage. In that case, 117V RMS would equal 165V peak. The post I responded mentioned "110 to 120", supposedly referring to the permitted range of supply voltages. This differs from 165V.

For some unknown reason, 250V got neglected when I made that list so I fixed the omission.

If the permitted range is still 110V to 130V, the lower end is not

117V.

Older people do usually refer to "110V" or "220V".

Since the text from [e-mail], that I responded to got snipped, here it is below. I was wondering where the specific number of 117 came from:

IIRC, if you calculate the actual rms voltage, a "110" or "120" volt line is actually 117v. Of course this is nominal, since it excludes noise and IR drops.

[Chris Lewis]

According to Mark Lloyd :

That's what I was answering.

You're getting confused. 110 to 120 (or more actually like 130) is the permitted _RMS_ supply voltage range. The sinusoidal peak is indeed in the 165V range.

Okay....

I wasn't saying that 117V was the lower range. I was actually referring to the practise of many motors having a _plate_ rating of thus-and-so Amps at 110V.

You answered that yourself.

[Mark Lloyd]

"110 to 120" is a quote from a particular poster. See the end of my previous post.

Why would you think I'm confused? Do you disagree with what I said about 117V RMS = 165V peak? About peak being 1.414 of RMS?

[snip]

[Chris Lewis]

According to Mark Lloyd :

Neither. I was remarking on this:

My posting did say I agree with your RMSPeak calculations. But saying the peak voltage isn't in the permissible (RMS) voltage range is rather odd way of discussing this, don't you think?

[Mark Lloyd]

And that's why I said it. I mentioned peak to demonstrate it NOT explaining the use of ONE PARTICULAR VALUE (117).

BTW, I accept "110 to 130" as being more applicable than "110 to 120". This still does not explain what is so special about that particular value (117).

[Chris Lewis]

According to Mark Lloyd :

As I said before, I vaguely recollected that 117V was used in the vernacular because it was the exact RMS conversion of some "standardized" nominal peak voltage. But I've not been able to find any corraboration in Google. The pecularity gets worse when you see documents referring to main supplies as 117/230V, when the latter really should be double the former to be logical.

We may simply have to dismiss it as a "historical quirk"/"common usage". Eg something approaching slang.

[Mark Lloyd]

OK. Thanks for answering my question.