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May 3, 2018 12:29 PM Subscribe
We need to buy a home air conditioner that will be plugged into a dedicated 240V socket. What's the best thing to do here?
Our apartment in NYC came with an old air conditioner from the 80s that plugs into a dedicated 240V 15A socket that I believe is an NEMA 6-15. From what I recall when we just moved in, it's wired the way it is supposed to be with nothing else but that one socket on the circuit. Now we need to buy a new AC and I have a few questions:
-Is there any point in getting a 230V air conditioner for 12-15K BTUs? They seem to be more expensive with no added benefits.
-How do I figure out (before buying it) whether a 115 V air conditioner bought new in 2018 can take both voltages?
-If it can take 240V, is all I need a plug converter for the NEMA 6-15 to 5-15?
-If it can only take 115V, do I need a step-down converter? If so, can you point to a decent one because all I am finding is converters for international travel that don't come with a NEMA 6-15 adapter.
-Do I need to be concerned about amperage? Is there any chance that an apartment building wired for 15A everywhere else would be wired for 30A at the dedicated 240V socket? Can I tell the 6-15 and 6-30 apart on sight?
Our apartment in NYC came with an old air conditioner from the 80s that plugs into a dedicated 240V 15A socket that I believe is an NEMA 6-15. From what I recall when we just moved in, it's wired the way it is supposed to be with nothing else but that one socket on the circuit. Now we need to buy a new AC and I have a few questions:
-Is there any point in getting a 230V air conditioner for 12-15K BTUs? They seem to be more expensive with no added benefits.
-How do I figure out (before buying it) whether a 115 V air conditioner bought new in 2018 can take both voltages?
-If it can take 240V, is all I need a plug converter for the NEMA 6-15 to 5-15?
-If it can only take 115V, do I need a step-down converter? If so, can you point to a decent one because all I am finding is converters for international travel that don't come with a NEMA 6-15 adapter.
-Do I need to be concerned about amperage? Is there any chance that an apartment building wired for 15A everywhere else would be wired for 30A at the dedicated 240V socket? Can I tell the 6-15 and 6-30 apart on sight?
1) Often times 240V A/C units also have heating capacity in the US. Do you need the ability to heat the space in winter / do you have adequate heating in the space? Also, a BTU calculation really depends on the square footage of space that you are cooling - how large is the room/apartment you are cooling?
2) Rarely will a 115V AC take both voltages. Almost always the product will have a spec(ification) sheet or a manual that you can use to double-check.
3) NEMA 5 plugs are rated to 120V maximum, so you should not be using a 5-15 adapter or converter at any point with that outlet. You want a NEMA 6-15 female to 6-20 male.
4) You could use a step-down converter but in my experience, the converter itself is expensive and uses energy.
5) You can either check your breaker panel and see which one has a 240V breaker (they may be two breakers ganged together) or can measure the gap between the outlet holes.
posted by suedehead at 12:57 PM on May 3, 2018 [1 favorite]
2) Rarely will a 115V AC take both voltages. Almost always the product will have a spec(ification) sheet or a manual that you can use to double-check.
3) NEMA 5 plugs are rated to 120V maximum, so you should not be using a 5-15 adapter or converter at any point with that outlet. You want a NEMA 6-15 female to 6-20 male.
4) You could use a step-down converter but in my experience, the converter itself is expensive and uses energy.
5) You can either check your breaker panel and see which one has a 240V breaker (they may be two breakers ganged together) or can measure the gap between the outlet holes.
posted by suedehead at 12:57 PM on May 3, 2018 [1 favorite]
A/C's are not dual voltage.
A transformer for 220->110 that can handle a 10Amp or higher a/c looks to be in the 150-300$ range, and im not certain if those are rated for continuous usage. They are also physically large, may have fans, etc.
tl;dr. Get a 220V A/C or have things rewired.
posted by TheAdamist at 1:04 PM on May 3, 2018
A transformer for 220->110 that can handle a 10Amp or higher a/c looks to be in the 150-300$ range, and im not certain if those are rated for continuous usage. They are also physically large, may have fans, etc.
tl;dr. Get a 220V A/C or have things rewired.
posted by TheAdamist at 1:04 PM on May 3, 2018
If you're asking these questions, you should have an electrician in to do the work. However, here's some info to arm yourself with.
A 230 (or 240)V unit is going to pull half as many amps as a 115V unit of identical BTU cooling capacity.
In a 115V circuit, (for these purposes, 110=115=120V), there's a hot leg, a neutral, and a ground. The neutral stays at 0V, and the hot leg alternates between +115 and -115.
In a 230V circuit, there's two hot legs, a neutral, and a ground. Each of the hot legs is like the 115V hot leg, but they're out of synch, so when one is at +115, the other is at -115. So they're always 230V apart from each other.
Residential wiring almost always comes in 230V. Half of your 115V circuit breakers are on one leg, and half are on the other. The only circuits that use both legs are those 230V like electric ranges, dryers, whole-house HVAC units, and some air conditioning units (like you're considering).
You're not going to be transforming anything. That would be like using a car as training wheels for a motorcycle.
So. You have an outlet of some species of 230V. It's connected to some wires, and those wires to a circuit breaker. Those existing wires, if they were installed with the idea of running a 230V AC unit, may not be rated to carry enough current to safely supply a 115V window unit.
If they *are* large enough (12ga=20 amps), you're golden. Just put in a 115 breaker, attach one hot wire to it, that wire (and ground and neutral) to the plain 'ol 115 20A outlet, and abandon the other hot wire (cap both ends). However, I wouldn't bet on that.
One last thing: Get more BTU than you think. AC units seem to be rated using dry climates. NYC is not a dry climate. If the box says it's good for a 30'x10' space, it's only good for 20'x10' space in the worst part of the summer. If you have 12' ceilings, 15'x10'.
posted by notsnot at 1:59 PM on May 3, 2018 [2 favorites]
A 230 (or 240)V unit is going to pull half as many amps as a 115V unit of identical BTU cooling capacity.
In a 115V circuit, (for these purposes, 110=115=120V), there's a hot leg, a neutral, and a ground. The neutral stays at 0V, and the hot leg alternates between +115 and -115.
In a 230V circuit, there's two hot legs, a neutral, and a ground. Each of the hot legs is like the 115V hot leg, but they're out of synch, so when one is at +115, the other is at -115. So they're always 230V apart from each other.
Residential wiring almost always comes in 230V. Half of your 115V circuit breakers are on one leg, and half are on the other. The only circuits that use both legs are those 230V like electric ranges, dryers, whole-house HVAC units, and some air conditioning units (like you're considering).
You're not going to be transforming anything. That would be like using a car as training wheels for a motorcycle.
So. You have an outlet of some species of 230V. It's connected to some wires, and those wires to a circuit breaker. Those existing wires, if they were installed with the idea of running a 230V AC unit, may not be rated to carry enough current to safely supply a 115V window unit.
If they *are* large enough (12ga=20 amps), you're golden. Just put in a 115 breaker, attach one hot wire to it, that wire (and ground and neutral) to the plain 'ol 115 20A outlet, and abandon the other hot wire (cap both ends). However, I wouldn't bet on that.
One last thing: Get more BTU than you think. AC units seem to be rated using dry climates. NYC is not a dry climate. If the box says it's good for a 30'x10' space, it's only good for 20'x10' space in the worst part of the summer. If you have 12' ceilings, 15'x10'.
posted by notsnot at 1:59 PM on May 3, 2018 [2 favorites]
As mitheral suggests, the simplest solution is just to bite the bullet and get a new 240V air conditioner. You can't plug a 120V air conditioner into your existing socket with any kind of adapter.
If you really want to convert to a 120V air conditioner, then you will have to get an electrician to replace your receptacle and rewire your panel box. Fortunately, this is pretty simple since you have a NEMA 6 with a real ground wire. The electrician will just leave the black leg connected to hot and change the other wire to neutral. He will replace the double pole breaker in the panel with a single pole breaker and fill the hole with a cover plate.
If the wire used for neutral is not white, for example, red, then both ends of that wire should be covered with white tape to indicate that it is neutral. The bare wire remains ground.
The electrician should check the gauge of the wire. If it is 14-gauge, then use a 15-amp breaker. If 12-gauge, then you can use a 20-amp breaker. Either should be sufficient since you can buy a 120V 15,000 BTU air conditioner that only uses 12 amps.
You will have to decide if the cost of an electrician is worth the savings on a smaller 120V air conditioner.
If you decide to go with a 240V replacement air conditioner, make sure the one you choose has a 15A plug (two horizontal blades) and not a 20A plug (one blade vertical and one blade horizontal).
posted by JackFlash at 4:20 PM on May 3, 2018
If you really want to convert to a 120V air conditioner, then you will have to get an electrician to replace your receptacle and rewire your panel box. Fortunately, this is pretty simple since you have a NEMA 6 with a real ground wire. The electrician will just leave the black leg connected to hot and change the other wire to neutral. He will replace the double pole breaker in the panel with a single pole breaker and fill the hole with a cover plate.
If the wire used for neutral is not white, for example, red, then both ends of that wire should be covered with white tape to indicate that it is neutral. The bare wire remains ground.
The electrician should check the gauge of the wire. If it is 14-gauge, then use a 15-amp breaker. If 12-gauge, then you can use a 20-amp breaker. Either should be sufficient since you can buy a 120V 15,000 BTU air conditioner that only uses 12 amps.
You will have to decide if the cost of an electrician is worth the savings on a smaller 120V air conditioner.
If you decide to go with a 240V replacement air conditioner, make sure the one you choose has a 15A plug (two horizontal blades) and not a 20A plug (one blade vertical and one blade horizontal).
posted by JackFlash at 4:20 PM on May 3, 2018
notsnot: "A 230 (or 240)V unit is going to pull half as many amps as a 115V unit of identical BTU cooling capacity."
Everything else being equal that is true but SEERs on A/C equipment have increased dramatically. This outlet was likely put in to handle a cooling load that required more power than a 120V outlet could provide but may be handlable by a more efficient unit now. You can get 15K BTU units now that run on 15A 120V circuits which was unheard of 30 years ago.
notsnot: "In a 230V circuit, there's two hot legs, a neutral, and a ground."
There probably won't be a neutral in a box servicing a 6-15 receptacle; just two hot legs.
However in the unlikely event there is a neutral there one could install a simple 120/240 volt duplex receptacle and be ready for anything.
posted by Mitheral at 6:56 PM on May 3, 2018
Everything else being equal that is true but SEERs on A/C equipment have increased dramatically. This outlet was likely put in to handle a cooling load that required more power than a 120V outlet could provide but may be handlable by a more efficient unit now. You can get 15K BTU units now that run on 15A 120V circuits which was unheard of 30 years ago.
notsnot: "In a 230V circuit, there's two hot legs, a neutral, and a ground."
There probably won't be a neutral in a box servicing a 6-15 receptacle; just two hot legs.
However in the unlikely event there is a neutral there one could install a simple 120/240 volt duplex receptacle and be ready for anything.
posted by Mitheral at 6:56 PM on May 3, 2018
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I've never seen an window/wall unit that is dual voltage.
A transformer large enough to run an A/C is pretty hefty; not a regular travel unit.
A 6-30 is physically much larger than a 6-15. If the socket you have looks the same size as a regular socket you have a 6-15. Also 30A at 240V is a lot of power; your A/C would be huge to require that much power.
However the best way to tell would be to look at your breaker panel and see what size breaker is feeding that ciruit.
An electrician can swap your 240V receptacle and breaker for a 120V unit. This would be the safest, most practical option.
posted by Mitheral at 12:53 PM on May 3, 2018 [3 favorites]