Be aware that electricity is very dangerous, so don't play around with plugs unless you know what you are doing (and make sure they aren't connected). They work by breaking the circuit when the current in the neutral wire is less than in the live. The equation triangle below shows the important relationship between power, current and voltage. Now we look at how you can calculate the cost of individual appliances: could help you save money on the electricity bill. The nominal impedance Z = 4, 8, and 16 ohms (loudspeakers) is often assumed as resistance R. P = power, I = intensity, E = electro motive force (EMF = voltage), V = voltage, potential difference, R = resistance. Formula 1: Electric power P = V ? I - where power P is in watts, voltage V is in volts and current I is in amperes. If you are opening a coffee shop, you will be buying equipment and acting as a "go between" between your electrician, and the dealer of your equipment (hopefully, TheCoffeeBrewers).
And keep in mind that if you deal with TheCoffeeBrewers, we will be happy to talk directly to your electrician for you if you would like. When you speak to many other dealers, you will be told that you need 220 Volts or 240 Volts or 208 Volts, or even 230 Volts.
The truth is that many dealers don't understand anything about electricity, and don't want to admit this to their customers. This is the most difficult section in this article, since it brings in a small amount of Physics.
The most common way that electricity is generated is by rotating a circular coil of wire about an axis through the coil's diameter so that the rotation is perpendicular to a strong magnetic field. According to Maxwell's equations, a current will be induced in the coil of wire as it rotates.
As should be clear in the drawing, when the coil is perpendicular to the magnetic field, the maximum amount of magnetic flux is passing through it. In fact, the magnitude of the induced current will oscillate as a sinusoidal wave as shown in the figure below. Power is transmitted from power plants at tens of thousands of Volts (up to four hundred-thousand Volts) along special cables to local distribution centers.
It is far too dangerous to transmit power at tens of thousands of Volts through residential neighborhoods on telephone poles. If you look up to the top of the telephone pole near your home, you will see a large can-shaped gadget with wires going into it.
And of course the reason that the waveform is 60 Hertz is because the coils of the generator (at the power plant) are spun at this rate. This difference in frequency can make a difference in fine electronic appliances that use small voltages and electronic filters to process things like audio and video signals.
Unlike the real Ground, the "Common" ground is an active part of the circuit, and it will have current flowing in it when an appliance is running.
This keeps the chassis at "ground potential," which is the voltage that the people standing around the appliance should be at.
If you open up the outer insulation on a power cord, you will find two or more insulated wires (that is, wires with plastic coatings) inside of it, and a single bare (uninsulated) copper wire.
The Voltage associated with an electron is its potential energy, whether or not it is actually moving (flowing). The power is the energy that is used up over time (power is the time-integral of energy), and is equal to the amount of electrons that flow times the potential energy of those electrons (which manifest as energy and make your appliance work). The medium through which electricity (or water) flows will resist that flow to a greater or lesser extent, depending on what the medium is. This means that the voltage across the appliance (which is the voltage difference between the electrical input ("Hot") and electrical output ("Common") of the appliance) is proportional to both the magnitude of the current flow, and the resistance of the appliance (or wire).
Because wire has resistance, and because it may run hundreds of feet, some of the voltage is lost in the wire by the current flow (as it flows to where it is needed) in accordance with Ohm's Law.
Electricians decide what gauge of wire is required for a circuit depending on the peak amount of current that the devices on that circuit can draw, and on the length of the wire. If the electrician uses a wire that is too thin for the amount of current needed at a given distance, not only will there be a large voltage drop in the wire (and the attached appliances may not work the way they should), but you can literally burn up the wire, and maybe start a fire.
In the figure above, the nominal 240 Volts and 120 Volts are the outputs of the transformer out on the street.
So when some appliance specifications say "240 Volts," and other appliance specifications say "220 Volts," they are not referring to different power requirements.
Note that in Europe, a new standard that many countries (including Italy) are using is 230 Volts at 50 Hertz.
Remember, the specification is telling you the power (Watts) and current (Amps) assuming that the appliance is running at 230 Volts. In the main electrical panel in your building (where all of the circuit breakers are), Phase 1 and Phase 2 "zig zag" down the panel so that in each bank of circuit breakers (the left side, and the right side), every other breaker is powered by the same phase (that is, adjacent breakers are powered by different phases). It is interesting (although not important to us) to note that if the current drawn in each phase is the same, then since they are exactly out of phase, the current flowing in the Common return will be zero. Each single circuit-breaker in the panel controls an independent (from the other breakers) 120 Volt AC circuit. In all of the discussion and figures above, we spoke about 240 Volts as if it worked the same as 120 Volts.
To deliver 240 Volt power to an appliance like a commercial espresso machine, we connect the "Hot" terminal of the appliance to one 120 Volt phase, and we connect the "Common" terminal of the appliance to the other 120 Volt phase. Note that if you subtract the Red curve (Phase 1) from the Blue curve (Phase 2), you get the 240 Volt waveform shown in Black. And by the way, if we return the discussion to the basement, the reason that the two phases are "zig-zagged" back and forth down the center of your main electrical panel is exactly so that any two adjacent slots in the panel will be on different phases.
When we connect 240 Volts to an appliance in this way, we know that the "Common" terminal on the appliance is moving up and down with 120 Volt amplitude at 60 Hertz, but the appliance doesn't know this. Because the 240 Volt AC difference is generated from two 120 Volt "phases," some people will call this "240 Volt two-phase power." This is meaningless.
Some industrial facilities (and also some rural areas) have "three phase power" instead of two phase power. Three phase power is generally used in applications where large electrical motors need to be driven. The way that high voltage is derived from three phases is exactly the way it was derived from two phases.
For the two phase system, the two phases are exactly out of phase (shifted by 180 degrees), so that the magnitude of the waveform becomes twice that of the phases: 2 X 120 Volts = 240 Volts. While going down to 208 Volts is not too big of a stretch from 212 Volts, remember that we need to allow for an 8% line loss in the 208 Volt system as well.
Except for manufacturers of large electrical motors, when 208 Volts is mentioned in the specifications, it is not that they are advocating 208 Volts as a "best" operating point. Standard 120 Volt household appliances (by and large) all have the same standard plugs on the ends of their power cords, and those plugs can be plugged into any standard household outlet. The main reason for having different plugs is to ensure that the appliance does not exceed the current limit of the wiring in the wall. If your appliance will draw 25 Amperes (and you should look at the specification), you would not want to plug it into a 20 Ampere circuit, because you will trip the circuit breaker (if you are lucky) or worse. Make sure that the circuit that your electrician installs will comfortably handle the current that your appliance will pull. Another reason (other than current) that you might have different kinds of plugs is that some plugs have a "key" (one prong with a different shape) if there are two "Hot" inputs and a "Common" input.


And a final reason is that some plugs are made to "lock" into their socket with a slight twist after the plug is inserted.
In the first place, there will be plenty of equipment in a professional kitchen that will make volatile gasses explode just by using the equipment the way it is intend to be used. Second, you are interested the current and the power for different reasons, and the manufacturer tries to give you the numbers that you probably want. And finally, most appliances appear (to the power delivery circuit) as things that are a little more complicated than simple resistors. The effect of the reactive component (2i Ohms in this case) is to put the voltage and the current out of phase with each other.
Except for the previous few paragraphs, if you've read and (more or less) understood this article, you should be comfortable looking at the commercial espresso machines specifications, and you should have no problem speaking with your electrician about what needs to be done.
P = power, I or J = Latin: influare, international ampere, or intensity and R = resistance. V = voltage, electric potential difference Δ V or E = electromotive force (emf = voltage).
The apparent power S is calculated according to Pythagoras, the active power P and reactive power Q.
Charge Q, (unit in ampere-hours Ah), discharge current I, (unit in amperes A), time t, (unit in hours h). Not only that, but you will be told that it has to be "single phase" voltage, or that it has to be "two phase" voltage. So instead, they will repeat some credible sounding nonsense that they've heard, re-read the spec-sheet to you (as if you can't read it yourself), and tell you to "go talk to your electrician" (as if you might not be quite smart enough to understand what they don't understand).
The purpose of this article is to demystify it for you so that you can talk directly to your electrician, and be comfortable with what needs to be done. And you don't really need to understand this part anyway, so don't despair if you find it confusing. The size of the current is proportional to the number of loops in the coil, and also to the rate at which the magnetic field is changing. When the coil is perpendicular to the magnetic field, the maximum amount of surface area (inside the coil) is exposed to those magnetic field lines.
This figure shows two common voltages that we are familiar with in our households, and in office buildings. It is much more efficient to transmit power at extremely high voltage, because it takes much less current to do so. Generally, there will be a power distribution station somewhere near you, and power will be sent into your neighborhood at 7.5 Kilovolts (7,500 Volts). For the most part, motors and heaters (as are used in restaurant appliances) do not care too much what the frequency is, as long as it's in this general range. Every electrical plug will have at least two prongs, and usually three (and sometimes more). It is wired to a metal electrode that is driven deep into the actual ground so that it makes good contact with the cold damp Earth.
After all, the people are standing on the ground (unless there is a carpet, in which case you can build up some charge, and get a "shock" when you touch the appliance). They are different things, but they manifest as one another in simple circuits, so are sometimes naturally discussed in this way.
Voltage is denoted "V," and is measured in "Volts." It is exactly analagous to the potential energy of a drop of water.
The amount of resistance is literally called "Resistance," is denoted "R," and is measured in "Ohms." For example, a narrow pipe will "resist" the flow of water more than a wide pipe, which will resist the flow of water more than a waterfall.
And a power line can run hundreds of feet from the transformer (up on the telephone pole, or in the ground on your street) to your house or building.
They are allowed a maximum of an 8% voltage drop in the wire, after which they are required to use a heavier (and more expensive, and harder to work with) gauge of wire. Have you ever picked up an extension cord with too many things plugged into it that felt hot? By the time these voltages get to your building, go through the electrical panel, then get back upstairs and through the walls to your espresso machine, they could have lost as much as 8% of the voltage.
They are just making different assumptions about where the equipment is plugged in relative to the transformer.
We've already explained that the "50 Hertz" piece of it does not matter to the appliances that we are concerned with.
The specifications were written for the European market, but the appliance will work just fine in the U.S. That is to say, we talked about a single sinusoid of 240 Volts (or of 120 Volts), having a "Hot" voltage wire (or terminal) and a "Common" return wire (or terminal). It is a first 120 Volt AC power line (shown in Blue), a second 120 Volt AC power line (shown in Red) that is running ? of a cycle behind the Blue power line, and a Common return shared by the two AC signals. The breaker outputs run to the various circuits in your house and building, and all share the "Common" return. In fact, two-phase power was conceived partly for this reason, to save on the cost of the wires. The fact that half of your outlets are on one phase, and half on another doesn't matter, as long as you don't connect the two phases together.
Specifically, we spoke about a "Hot" line (120 Volts or 240 Volts) and a "Common" line (which is 0 Volts). What the appliance "sees" is then the voltage difference between the two phases, as shown in the figure below.
From the point of view of the appliance, the appliance "sees" the power as a single phase 240 Volt signal.
In this case, the appliance will use the phase going to its "Hot" terminal as the 120 Volt AC input, and will regulate this down to a few DC volts relative to the 0 Volt "Common" ground. For this reason, many commercial appliances are shipped without a plug at the end of the power cord. For high voltage outlets, there are 20 Ampere sockets, 30 Ampere sockets (these are what you will likely see), and various others.
The good news is that you will not be able to plug it into a 20 Ampere circuit because the 30 Ampere plug on your appliance will not fit into a 20 Ampere outlet. For commercial espresso machines, 1-group machines will draw about 15 Amperes, and can work on a 20 Ampere circuit.
This is to make sure that the "Common" input gets connected correctly, because the machine will know the difference.
If you look at some of the specifications of our commercial espresso machines (in which all three numbers are given), you will see that this equation doesn't seem to hold.
You probably want to know the peak value of the current (that is, the maximum current that the machine could draw at any instant). Instead, you'd like to know the average power, because this is what will drive your electric bill.
You might recall that in a single instance above, we used the word "impedance" instead of "resistance," and said that we were not going to discuss it.
In addition to resistance, appliances (and wires) also have capacitive and inductive elements that behave differently at different frequencies. So when calculating power, you can't simply multiply the amplitudes of the voltage and current, and divide by the square root of 2.
In fact, your electrician probably doesn't know this either, and certainly doesn't worry about it.
If you have any questions, or if you'd like us to speak to your electrician too, just drop us a note, or give us a call.


Note also that when the coil is face up, the induced current will be moving in the opposite direction as when the coil is face down. As we will discuss below, "Ohm's Law" dictates that the higher the voltage, the lower the current, hence the less Voltage will be lost. In Europe (where many of the commercial espresso machines are made), the standard frequency is 50 Hertz.
Nominally, "Common" should be at 0 Volts, which is why it is the reference point for the power line.
Within an appliance, the building ground is connected to the appliance chassis, and to all metal parts that a person could touch. If anything goes wrong inside of the appliance, and the live voltage somehow gets connected to the chassis (usually because of a worn wire), the appliance will short-circuit the live current directly to the Earth, and a circuit-breaker will trip.
If the drop of water happens to be at the top of a waterfall, its potential energy is very large, because it can fall and exert force.
Therefore equipment that is specified at 240 Volts should be expected to work at 220 Volts.
In practice, the equipment should work anywhere in the 220Volt - 240Volt range, since the manufacturer can't know the actual voltage at the socket into which you are going to plug the appliance. In Europe, the 230 Volt appliances must also work with an 8% line loss, so they must work all the way down to 212 Volts. In fact, the power coming out of the stepdown transformer on the telephone pole near your building has three different wires, but they are not 120 Volts, 240 Volts, and Common. This is called "two phase power," because there are two "phases," which (in this case) are 180 degrees apart.
Each circuit breaker is designed to "trip" when a specified current limit is exceeded, which disconnects the circuit from the voltage source. A 240 Volt circuit breaker is twice the width of a 120 Volt circuit breaker because it occupies two (adjacent) slots in the panel. This makes the other terminal (to which we've connected the other phase of the 120 Volt line) "look like" it is connected to a 240 Volt AC power line.
This is irrelevant to commercial kitchen appliances, but if the building that you are in has three phase power (which is possible but unlikely), you need to understand it too.
Most (but not all) 240 Volt appliances will work at 208 Volts, but you will not get the same performance out of them. For commercial espresso machines, the difference is that the power will be lower (than what is specified for 240 Volt operation), and it will take the boiler longer to warm up in the morning.
There are different kinds of plugs and different kinds of outlets for high voltage, and they are not compatible. The person doing the installation first looks at the outlet, and then provides a compatible plug which they put on the end of the power cord as part of the installation procedure. If your appliance will draw 18 or 19 Amperes, don't try to "squeak by" with a 20 Ampere circuit.
2-group machines will draw close to 20 Amperes, and should not be put on a 20 Ampere circuit. If you intend to plug other appliances into this same circuit, you need to add up the currents from all of the appliances, and put in a circuit that can handle the total current. Some zoning boards will require this as a "safety feature." They are concerned that if someone trips over the cord, the plug will get pulled out, and there could be a small spark (like miniature lightning) that would cause any nearby volatile gasses to explode. This "safety requirement" is just a rule that makes sure that if someone accidentally trips over the cord, the cord will hold firm so that they go down hard.
To calculate power, we are really interested in the area under the curve, and not in the peak of the curve.
So the two numbers given in the specifications are not meant to be consistent with each other. If you really want to know the power, you have to know the complex impedance, the operating frequency (or the frequency components of waveforms that are not pure sinusoids - which can be found with Fourier transforms), and the phase shift that the impedance will induce in the current at the operating frequency (or frequency components). So when you are talking to him or her, don't bring this up unless you are trying to intimidate them. This probably isn't intentional, but it can get very confusing to someone who isn't quite familiar with electricity. This means that on every half rotation, the current will change from positive to negative, and back again on the next half rotation. The coils are made so that the ratio of the number of loops in the two coils creates the "stepdown" in Voltage. Because "Common" it is nominally 0 Volts, it is sometimes casually referred to as "Ground," although it is not the same Ground as the building Ground (which is the real Ground). Among the insulated wires, there will be a white one, a black one, and if there are more wires, these should be colored too. You should not touch them unless you know that they are not connected to anything, or unless you know that the circuit breaker has been turned off at the main panel. If it is at the bottom of the waterfall, its potential energy is zero, although it is the same drop of water.
To get the total resistance, you have to multiply this number by the length of the wire (in feet).
Like the pipe that will burst if too much water is run through it too quickly, a wire will burn itself up if too much electrical current is run through it. Similarly, lights and appliances that are specified as using 120 Volts should be expected to work at 110 Volts. If you look at the circuit breakers in your main panel, you will see numbers on them like "15" and "20." These numbers specify the amount of current (in number of Amperes) that will trip the circuit breaker. The appliance has no way of "knowing" that its common terminal is not sitting still at ground potential (0 Volts). In Trigonometry, we would say that they were "120 degrees out of phase" from each other as shown in the figure below.
If the manufacturer specifically mentions 208 Volts as an operating point (as does FAEMA), the equipment will certainly work.
In our example above, where we posited an espresso machine having an resistance of 10 Ohms, and an impedance of 9.8 + 2i Ohms, the "imaginary" 2i part is the part that will shift the phase of the current. Note that the potential energy depends only on the position of the drop of water, and not on whether it is in motion. The higher voltage, 240 Volts, is used for large appliances, like commercial espresso machines.
That the single phase 240 Volt waveform happens to be generated by the transposition of two 120 Volt phases doesn't matter to the appliance. Note that machines that are built for the European market in which the standard voltage is 230 Volts must work at 212 Volts to allow for an 8% line loss. And the amount of the shift would be different in Europe (at 50 Hertz) than it would in the U.S. The drop of water does not change when you change its position; only its potential energy changes. This is simply our standard way of providing 240 Volts, and the machine can't tell the difference. But its impedance might be 9.8 + 2i Ohms, where i represents the square root of -1 (which is imaginary).



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