Installing window air conditioners
May 16, 2004 9:20 AM   Subscribe

I have an old house with old wiring in the walls. The question inside is about installing window air conditioners.

Old wiring doesn't necessarily= dangerous, in fact I have had an electrician go over the house thoroughly, upgraded the service coming in to modern levels, replaced the main box etc. Problem is, the bedrooms have no grounded outlets, and I want to put window air conditioners (with 3-prong, grounded plugs) in those rooms. Ordinarily I would just use an adaptor, but the owner's manuals seem to really freak out about this, seems like more than just the usual liability CYA type of warning language. What exactly is the risk if I use an adaptor, and are there any safe alternatives to ripping out walls and replacing the wiring within? These are small 5000 BTU airconditioners going in bedrooms on the second floor with no easy access to the basement (where plenty of new, grounded outlets exist).
posted by stupidsexyFlanders to Home & Garden (21 answers total)
Can you replace the old, non-3-prong outlets with modern ones? (I had a similar experience in my building; the landlord sent out an electrician and simply put new outlets wherever I needed it (AC/TV/Computer))
posted by BlueTrain at 9:47 AM on May 16, 2004

A good electrician won't have to rip out walls. Get an estimate on adding new plugs, as it shouldn't run you more than a few hundred dollars to do what you need.
posted by machaus at 9:53 AM on May 16, 2004

Perhaps I'm missing something here; the electrician that was sent up took all of 15 minutes to install 3 new outlets. What don't I know about this situation?
posted by BlueTrain at 9:57 AM on May 16, 2004

Cut the breaker and take the outlet out of the wall. Invest in a cheap voltmeter to test and make sure the power is cut off. If there are three wires you are in good shape, assuming one of those wires is wired to ground. If there are only two wires coming in you won't have a ground and you'll need another wire. It would be possible to put a ground wire along the outside of the wall and put it in a grounded outlet in another room. 10 or 12 gauge wire should be good for this.
posted by estey at 10:04 AM on May 16, 2004

I should clarify: If there are three wires, you are in good shape, but you'll need to purchase a new three-prong outlet from Home Depot or Lowe's. The third wire that previously wasn't wired to anything will be wired to ground in the new three-prong outlet you install yourself with a screwdriver.
posted by estey at 10:07 AM on May 16, 2004

You might not have to rip out all the wiring. If there are metal pipes nearby, they can probably serve as a ground. If you have radiators, you might even be able to use a 3-to-2 prong adapter and run a short wire from the third prong (the adapters sometimes have external copper tabs for it) to the radiator. If your radiators aren't grounded, then you could run another wire down in the basement. If you connect it to something that *isn't* grounded, though, you've just made the problem worse by extending the risk to

Here's a usenet thread about it.

I think the risk comes from the fact that the third prong grounds the case. If something inside shorts to the case, then it will usually go through the third prong, trip a circuit breaker, and shut things down. If the third prong isn't connected, it could just kind of sit there unchanged, but with the case now at high voltage. When unsuspectingsexyFlanders comes along and touches the case, he could fill in for the missing third prong and have that high voltage take a little trip through him.

Another thread about the risk.

On preview: Replacing just the plugs requires that the outlet boxes are already grounded. If there actually is no ground wire coming to them, putting in new plugs won't cut it. BlueTrain, just because the third hole is there, that doesn't mean it's grounded. You can get a little box you plug in that lights up to tell you if it's wired correctly, or the city inspector (if you have one) will usually have one.
posted by whatnotever at 10:08 AM on May 16, 2004

Oh, crap. Off to Home Depot I go.
posted by BlueTrain at 10:12 AM on May 16, 2004

whatnotever, thanks good link and explanation.

What about running the Air Conditioning unit through one of those power strips that has a circuit breaker built in, they are cheap. Would that turn the power off if the AC unit were to short out?

Also I think AC Units would be more likely to short out since theres lots of water potential around it (rain, ice, etc..) which why they they might stress the extra precaution.
posted by stbalbach at 10:20 AM on May 16, 2004

BTW--To test if a plug is grounded take a voltmeter or simple power tester with a neon lamp and plug it into the wall outlet. First, verify you have power by sticking the prongs in the two vertical slots. The lamp should light up. Now keep one prong in one of the slots and stick the other prong in the ground hole. If you don't get anything try switching to the other slot. When you measure the smaller slot (I think) to the ground hole you should get a reading. If you can't get a reading on either prong to ground your outlet is not grounded.

On preview--stbalbach, you shouldn't use a power strip with your air conditioner. When the compressor kicks in an air conditioner uses a LOT of power. This is why you have to use heavy duty extension cords to power an air conditioner. Smaller wire will get warm to the touch when you are drawing so many amps.
posted by estey at 10:24 AM on May 16, 2004

stbalbach, it's not the circuit breaker that you need. In addition to what estey said (and in fact the breaker in a little power strip might trip when the AC turns on), the circuit breaker will only turn off the power when a path to ground (possibly through a person) is completed. Something could short out inside, bringing the case to a high voltage, without any current flowing to trip the breaker until someone comes along and touches it.

The point of the third prong is that it gives the short to the case somewhere to "drain" immediately, which will trip the circuit breaker in your basement.

Also, if the short reaches ground through a person's body, the body might not draw enough current to trip the circuit breaker. In fact, I know that the times I've had wall voltage through me it was never enough current to trip a breaker. It was enough to hurt, though. (It was usually just through my thumb, not through anything important.)
posted by whatnotever at 12:36 PM on May 16, 2004

If you're worried about the condition mentioned by whatnotever, you can install a Ground Fault Circuit Interrupter (GFCI, or sometimes GFI) in place of the outlet into which you plug the A/C. The GFI will trip when it senses a current leak of a few hundred milliamperes, which often means that someone is getting shocked.

Running a ground wire from some nearby cold water pipe to the outlet in question is a good idea, and not that difficult depending on the configuration of your house. But, it sounds like you need someone that's familiar with house wiring to do that for you. A plumbing mistake gets you wet; a wiring mistake gets you dead.
posted by Daddio at 2:54 PM on May 16, 2004

Response by poster: Why does it have to be a "cold water" pipe? Because my radiators are really convenient to these air conditioners, and that's hot water.
posted by stupidsexyFlanders at 5:38 PM on May 16, 2004

One of the bigger worries is the number of amps your air conditioner will draw. When we had our addition built, we had an outlet put in for future use AC. It is on its own circuit so that it won't trip the breaker, blow a fuse, or turn the wires into heating coils inside the walls.,,,
posted by plinth at 5:56 PM on May 16, 2004

I think it might always say cold water pipe because that provides the best assurance that it's actually grounded. The cold water pipes are all connected and usually go directly into the ground. Hot water pipes go to the water heater and radiator pipes go to the furnace, neither of which is necessarily grounded. So like I said, you may need to ground whatever pipes you use in the basement, also. You're just using the pipes as a wire, so you should check where that wire goes.

This page mentions grounding issues with pipes in some of the last few paragraphs (find "appliance" in the page).

plinth has a good point. If your wiring is too thin, you may have a fire hazard. Thinner wires have more resistance. More resistance times the large amount of current the AC draws equals more power dissipation equals more heat. The cord on my AC itself is relatively thick and well-insulated, but it still gets very warm when the AC is running. Hmm... it looks like a 5000 BTU AC will draw less current than a microwave or a hair dryer, though. So my guess is it would be fine. Sorry, I don't want to alarm you. But I do recommend you ask someone who knows more, as opposed to an electrical engineer who never really liked the actual "electricity" part...
posted by whatnotever at 8:29 PM on May 16, 2004

Grounding to water pipes does carry some risk, as any short to earth will make all the plumbing in your house live.
posted by dg at 8:38 PM on May 16, 2004

Grounding to water pipes does carry some risk, as any short to earth will make all the plumbing in your house live.

That's sort of the whole point -- to trip the breaker (blow the fuse) when an internal voltage makes its way to the outside of the device. Since the current has a clear path to ground, it's not going to go through you if you touch the device or the pipe.
posted by kindall at 9:30 PM on May 16, 2004

Unless you have a Residual Current Device (also known as an Earth Leakage Circuit Breaker or Safety Switch), nothing will trip even if there is a dead short to earth. The best of these devices will also detect a difference between the active and nuetral wires and trip even if there is no leakage to earth. Circuit breakers or fuses generally only blow if the current exceeds the rating of the fuse or breaker. You should be safe if you touch a live plumbing fixture in this case, unless you yourself are grounded, when you may end up being the path of least resistance and, quite literally, toast.
posted by dg at 9:40 PM on May 16, 2004

dg, I'm confused. If there is a short to ground, won't that draw more current than the rating of any fuse or breaker? In the simplest case, if I stick a wire between the active socket and the ground socket, won't that that trip a breaker?
posted by whatnotever at 11:12 PM on May 16, 2004

You should be safe if you touch a live plumbing fixture in this case, unless you yourself are grounded, when you may end up being the path of least resistance and, quite literally, toast.

But the voltage difference between a grounded person and a grounded pipe is zero -- no zap. And the resistance of a metal pipe is much lower than the resistance of a human body; the current's going to follow the pipe, not you.

It could be very dangerous if you connect electrical ground to a pipe you think is grounded but isn't. In that case, yes, you've electrified your whole plumbing system and could get a nasty surprise if you touch a pipe while you are yourself grounded. Fortunately, this is not very likely to happen, because it is the nature of pipes to go into the ground.
posted by kindall at 11:55 PM on May 16, 2004

I think it should, whatnotever, but a friend of mine was killed a few years ago when he, while standing on the ground, grabbed a water pipe that had been used as a ground for the electrical system for his house and it was later discovered that there was a short to ground within the house. If the fuses were of the correct size, I guess they would blow with a dead short, but maybe there is a range where a short does not pass enough current to blow the fuse, but still enough to kill? On preview, kindall is most probably right - the pipe may have not been grounded until he grabbed it, perhaps by the original pipe (or a section of it) from the street being replaced with a plastic one or something.

Accidents like this were the reason ELCBs were made mandatory in any new construction here in Australia a few years ago. This gives some additional information, but doesn't really support my theory to any great extent. I do know that using plumbing systems as a ground is very much frowned upon here and that a separate grounding stake is required on new construction, but can't find any links to back me up :-(
posted by dg at 12:12 AM on May 17, 2004

If the same circuit is shared between the air conditioners, you could have a fire hazard if the fuse doesn't blow. If not, you are probably safe. Fun, isn't old wiring? An electrician will have the tools to discover how the home was wired. Then again, he'll have the tools to put in new wiring.

As far as grounding goes, replacing each of those outlets with a GFCI will provide lots of safety from electric shock. HOWEVER, your GFCI is not useful if you mix up hot and neutral, IIRC.

If your wiring is old enough to have only two prong outlets, the outlets may not be polarized. Can you plug in one of those new-fangled plugs with one blade wider than the other?

If you can't, call an electrician and don't even THINK about using a ground defeater.

If you can, you can hope that the plug was wired the right way around. Personally, I wouldn't trust anything that old. But that's just scared old me.

Did I mention that if you mix up hot and neutral on one plug, but not on another, even if it is a GFCI, when you touch the case of Appliance in plug A and touch the case of Appliance in plug B, you'll die without the GFCI tripping?

posted by shepd at 1:17 AM on May 18, 2004

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