My HVAC guy is telling me I need a 25 amp breaker and a 25 amp disconnect for my soon-to-be-installed central air compressor. I've asked him for more details but he's less than forthcoming. My assumption is that I will install: - a double pole 30 amp breaker on my breaker box (30 amp because they don't sell 25 amp breakers at my local big box store) - I'll run 10/2 NM from said breaker to a junction box on the interior of my house near the exit point. In that junction box, I'll splice to a weatherproof conduit and run out to the disconnect box. - The disconnect box will be a 60 amp disconnect (because, again, that's all they sell at the big box) but I'll get a fused version and put 25 amp fuses in there. Hopefully the HVAC guys will take it from there. Am I way off? Is a 30 amp breaker too much for the 25 amp requirement that my HVAC guy spec'd? In the US, it's required that manufacturers include the following items on condensing unit's nameplate (NEC 440.4(B)):

Minimum supply circuit conductor ampacity Maximum rating of the branch-circuit short-circuit and ground-fault protective device You'll simply use the minimum supply circuit conductor ampacity value from the name plate, and NEC 2011 Table 310.15(B)(16) through Table 310.15(B)(19) to determine the proper conductor size. As for the branch-circuit short-circuit ground-fault protection, you'll have to select one less than or equal to the maximum rating listed on the nameplate. However, you'll have to choose a device with a high enough rating to handle the inrush current, so you'll want to choose a device close to this value. To answer your questions directly... A 30 ampere breaker is the wrong one, if the nameplate lists 25 as the maximum rating of the branch-circuit short-circuit and ground-fault protective device. For 25 amperes, you're likely correct to use 10 AWG cable. Usually the disconnect is not fused, and simply functions as a safety disconnect.

You'll just have to make sure the disconnect is rated for greater than 25 amperes, and the appropriate voltage.Browse other questions tagged electrical air-conditioning or ask your own question.You can run your window air conditioner from an inverter. The most common way to use an inverter is when changing from alternating current, or AC, when going off the grid. By going off the grid, you will be using direct current, or DC electricity, from a sustainable energy source like solar, windmills or water. The inverter converts the DC current into AC current so that regular household appliances can be run from typical household sockets. The Electrical Basics An inverter is part of a 12-volt DC system. For practical purposes, it takes 11 amps of DC power to successfully run a 1-amp AC powered device. If you have a 5-amp window air conditioner, you will need 55 amps of DC power to run the unit continuously. However, all electrical appliances have a starting surge that gets the motor running.

This is generally five times the continuous electrical load, which means that, in this instance, you will need 275 amps of DC power to start the 5-amp air conditioning unit and then a continuous 55 amps to keep it running. 1 ton window ac best priceThe Air-Conditioning Unit The smallest window air conditioners that are designed for a single room, usually in the 5,000 BTU range, use about 4 to 5 amps of power when running. how much is a new 3 ton ac unitA larger whole house unit that puts out 12,000 BTU will use about 11 amps of power when running. choosing air conditioning unitThe surge on an 11-amp unit will be about 360 DC amps while the surge on a 4-amp unit will be about 130 amps. In this case, using the smallest air conditioning unit possible will enable you to use a smaller and less expensive inverter.

The Power Source In real terms, all the inverter does is to transfer a specified amount of power to operate any given AC electrical unit, including air conditioners. Although the inverter must be rated to accept the high amperage rating that an air conditioner will pull through it, all inverters get their power from a power source like storage batteries or direct hook-ups to solar panels, windmills or hydropower. These power sources must be capable of providing the needed surge power as well as the continuous energy needed to keep the air conditioner running. Charging In most cases, storage batteries will be used as the power source to run the air conditioner. These batteries will need to be charged on a regular basis. Alternate forms of sustainable power are almost always used to charge the batteries, including solar panels and windmills, among others. However, unless you are using hydropower, which guarantees a continuous source of sustainable power day or night, wind or no wind, a back-up AC grid hook-up can be used to charge the batteries on days when there is no sun or wind.

There's nothing better than air conditioning on a hot day. And the technology keeps getting cooler. The latest sleek-looking room air conditioners sport digital displays, timers, "smart" fans that automatically adjust speeds to maintain desired temps, and remote controls. They're also quieter, more energy-efficient, and easier to install and maintain than units made only a few years ago.Here are some of the most frequently asked questions, answered by our experts at the Good Housekeeping Research Institute.What are the different types of air-conditioning units?There are four main types of air-conditioning units. Window mounted: The most common type, window-mounted units temporarily slide into double-hung window openings. You can buy a cooling-only unit or a cooling/heating unit for supplemental heat if your home is located in an area with moderate temperatures.Pros: Low cost, most work with existing electrical wiring in your home, and they're easy to install. Cons: They're typically designed only for double-hung windows.

If you live in the north, it's best to remove units at the end of the season.Prices: From less than $200 for cooling a 100-square-foot room to $400 for cooling a 200- to 500-square-foot room. Step up to an $800 model and you can pick up a unit that cools and heats a 700- to 900-square-foot room.2. Wall-mounted: These room air conditioners are permanently mounted in a wall by attaching a metal sleeve through the wall and sliding in the AC chassis from inside. Wall-mounted units also come in cooling-only or cooling/heating varieties.Pros: Aesthetically appealing, fit more securely than window units, no storage necessary, easy to repair and replace. Best of all, if you have only one window in the room, a wall-mounted model will still let sunlight into the space.Cons: Installation can get costly — you must cut an opening through an outside wall, and larger units may require installation of a dedicated 220-volt line. What's more, many models don't include the exterior metal sleeve, so you'll need to purchase it separately (costing $50 to $100).

Prices: Range from roughly $400 for cooling a 400- to 700-square-foot room to $700 or so for cooling/heating a 1,000 square-foot room.3. Window/wall-mounted: This versatile type can be temporarily installed in a window or permanently mounted in a wall.Pros: Ideal if you're buying an air conditioner for, say, a rental apartment window and you may want to later install it in a home wall.Cons: Window/wall-mounted models generally don't include window installation kits — the nuts, bolts, and frame needed to secure the unit in a window. Depending on the plug type and/or amperage, you may need a dedicated 220-volt circuit.Prices: About the same as wall-mounted models.4. Portable: This is a mobile air conditioner on wheels that can be rolled from room to room and includes a tube to exhaust heat out of a window or through an opening in a wall.Pros: It's easy to store at the end of the season.Cons: Slightly higher-priced than comparable window units, eats up floor space, and the exhaust tube must be installed each time it's moved.

Prices: Range from about $700 for cooling a 150- to 300-square-foot room to $1,000 or more for cooling a 500-square-foot room.Learn 5 ways to save money on air conditioning from The Daily GreenHow do I find the right size unit for my room?Choosing the right size room air conditioner is as important as selecting a reliable brand. Shop for a model with a cooling capacity, measured in BTUs (British Thermal Units), that's appropriate for the square footage of your room. BTU figures typically range from 4,000 to 20,000 and more — the larger the room, the more BTUs are needed. But bigger is not necessarily better. An oversized unit will be costly to operate and won't run long enough to dehumidify the air, resulting in a "clammy" feeling. A too-big unit can also reduce air quality and aggravate allergies. And, buying a unit that's too small will be inefficient, too. Use our Air Conditioner BTU Calculator to find the right size unit for your room.Installation: Room air conditioners come in a variety of dimensions, so measure before shopping.

For window units, measure the height and width of the opening while the window is completely open.What are some key terms in air conditioning?Here are some terms that you should be aware of when shopping for an air-conditioning unit: Amperage: Most rooms have circuits rated for a total of 15 amps of electricity. Unless the space you're installing your air conditioner in has a dedicated electrical line, take note of the unit's amps, ranging from 5 to 15 or more. Large air conditioners with 12 to 15 amps can trip the circuit breaker. In that case, you may need a dedicated line.Dehumidification: This measurement gives you a rough estimate of how much moisture the unit removes from the air. It can range from one pint per hour to as many as 10. Higher-rate units are best for those who live in high-humidity areas.Efficiency: To find out how energy efficient a model is, look at the manufacturer's EER (Energy Efficiency Rating), which is the BTU (also known as the cooling output) divided by the power consumption in watt-hours.