Electricity (For Leases, Etc.) Explained And Possibly Demystified

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Nothing in today’s Ruminations posting should shock its readers.

We’re sure that more than a few readers know that calling for 600 amp electrical service doesn’t assure that you’ll get usable electrical service. Doing so only calls for one ingredient in the recipe that gets the place properly lit, the computers to run, the HVAC to work, and … well, you get the idea. Today, we’ll try to explain what those who throw electrical specifications around (like they know what they are talking about) might want to know. It won’t be easy because it’s somewhat technical, but we’ll try to make it simple (if not interesting).

To begin with, Ruminations would like to introduce readers to three guys from the 18th century. You’ll want to know them if you want to understand something about a user’s power requirements. The three are: André-Marie Ampère (France), Alessandro Volta (Italy), and James Watt (Scotland). They didn’t invent the electrical terms that you realize relates to their respective names. They were just honored in that way. This is also a good time to re-introduce Antoine-Laurent de Lavoisier (France, and you know him as the person who reputedly first learned that Oxygen supports combustion).

From this gang of three-plus, we get (respectively): amps, volts, watts, and the unit prefix, kilo (meaning, one thousand). Yes, “kilo” comes out of the thinking of Lavoisier and his scientific team, sometime in 1795. Let’s get this out of the way right now – a kilowatt is 1,000 watts; a kilovolt is 1,000 volts; and you get the idea. The prefix “kilo” is a multiplier, specifically standing for “one thousand.” [“Mega” stands for “one million”; there are lots of other prefixes, but you won’t come across them in this line of work.]

Amps [short for (surprise!), “amperes”], are a measure of current – how much electricity passes through a wire. Think water: a gallon would be one way to measure how much water passes through a pipe.

Volts are a measure of (electrical) potential difference (or “electromotive force”) between two points (in an electrical circuit) you might choose. Think “pressure” (such as in a water pipe) or “force” (such as pushing against a wall).

Watts measure the amount of power being used. A 120 watt light bulb consumes 120 watts of power. That means that the rate at which it consumes power is 120 watts. If you leave that bulb on for 10 hours, it will consume 1,200 watt-hours of energy (120 watts times ten hours). 1,200 watts is 1.2 kilowatts. 1,200 watt-hours is 1.2 kilowatt-hours. When we write about “kilowatt-hours,” we are writing about “energy,” not “power.” “Kilowatts” and “kilowatt-hours” are related by the factor of “time.”

[It’s time for some abbreviations. These are intuitive. A “watt” is abbreviated as “W.” A thousand watts (i.e., a kilowatt) is abbreviated as “kW.” Similarly, a “volt” is abbreviated as “V,” and a thousand volts (i.e., a kilovolt) is called a “kV.” An “ampere” is abbreviated as “A.” Finally, a “kilowatt-hour” is abbreviated as “kWh.”]

Commercial (and industrial) users of electricity care BOTH about power (watts, kilowatts) and energy (watt-hours, kilowatt-hours). That’s because their electricity bills are based on both. An electric meter keeps track of “how much electricity” was used. That measure of consumption is in kilowatt-hours. The commercial user’s electric meter also keeps track of the peak power demanded by the user in each billing period. That measure of consumption is in kilowatts. It is easy to understand that one would pay for what is consumed, just like for natural gas or water or gasoline. Those are measured in cubic feet or gallons. That’s also how electrical “energy” is paid for – specifically, by the number of “kilowatt-hours” consumed.

As to a user’s peak demand (measured in “kilowatts”), think a “standby” charge. Imagine a user had a humongous electric motor, one that draws a million watts of “power” (that’s a “megawatt”), but only runs it for one minute each month. That’s not going to “consume” much “energy.” [In fact, by our calculations, the energy so consumed is 16.67 kWh. A 100 watt light bulb burning for 10 hours each day in a 30 day month consumes 30 kWh that month, about twice what the humongous motor would consume.]

If all the user was operating was that single light bulb, the utility provider wouldn’t need a very big power plant or very thick wires. It only needs to be able, at any one time, to generate 100 watts of power. For the motor, however, even though its generating plant would sit idle 44,639 minutes every 31 day month just to be able to provide a megawatt of power during the other minute, someone has to pay for that size facility and the fat transmission wires needed for that one minute of glory. That’s why commercial users of electricity pay a “demand” charge for power as well as a “consumption” charge for energy.

[For a slight elaboration on how electrical usage is billed (and a discussion of submetering), click HERE.]

Hang on (Sloopy?) while we finally get around to explaining why asking for 600 amp service isn’t very informative and why we’ve told you about the Frenchman, the Italian, and the Scotsman.

Absent power losses, if the “pressure” of the electricity between two points of an electrical circuit (think, between the two prongs of a common electrical plug) is one volt and the amount of current [think, the amount of electrons (like the amount of water) flowing between those two points is one ampere, then the amount of power being drawn by whatever is using that electricity (think, a light bulb) is one watt. Yes, one amp of current at one volt of electromotive force equals one watt of power. A 120 watt light bulb draws one ampere of current when plugged into a 120 volt outlet (1 amp times 120 volts equals 120 watts). If you keep that light lit for one hour, it will consume 120 watt-hours of energy. [Whereas, the power of a car’s engine is measured in horsepower, the power of a light bulb is measured in watts. In fact, one horsepower (a measure of power) is equivalent to 746 watts (also a measure of power). Consuming energy to keep that light bulb lit is like burning gasoline to keep that car’s engine running. Are you getting it?]

The next seven sentences are for wonks only. There is a unit of measure called the “volt-ampere.” Like “watts,” it measures “power,” but not the kind of power that is “consumed” (by creating heat, light, etc.). A thousand “volt-amperes,” abbreviated “VA” is, as you would expect, a “kilovolt-ampere,” abbreviated, “KVA.” The difference between watts and volt-amperes is that a “watt” measures how much power is being “drawn” or “used,” whereas a “volt-ampere” measure “potential” power. The ratio of watts to volt-amperes (W/VA) is called the “power factor,” or “PF.” Volt-amperes tell professionals how big the wires, circuit boxes, and fuses or circuit breakers have to be, not how much the connected electrical devices are actually drawing.

Now, a typical space will has appliances that run on 120 volt and 240 volt circuits. [Today, 120 volts and 240 volts are the standard circuits. Today, when someone refers to a 110 volt or 115 volt circuit, they are really asking for a 120 volt one. Similarly, today, the standard 240 volt circuit covers the historic 220 and 230 volt circuits.]

A 120 watt light bulb will draw 120 watts of power whether it runs on (“is designed for”) 120 volts or 240 volts. The difference IS CRITICAL TO KNOW. As pointed out above, a 120 watt light bulb plugged into a 120 volt outlet draws one ampere (amp) of current, BUT in a 240 volt outlet, it only draws 1/2 ampere (amp) of power. That’s because 120 watts also equals 240 volts times 1/2 ampere equals 120 watts. (One-half of 240 is 120.)

This lets Ruminations get back to today’s opening paragraph where we derided a call solely for 600 amp electrical service. Users draws “power” as measured in watts. Yes, add up the wattage of all the light bulbs. Add up the wattage of all of the cash terminals. Add in all of the wattage drawn by the HVAC equipment. Don’t forget the employee refrigerator. In fact, don’t forget anything that uses electricity in the space. Suppose that adds up to 72,000 watts, or 72 kilowatts. Now, how much current (in amperes) will be needed to see that all of those things can run at the same time? Well, if the power supply is for 120 volts, we just divide 120 into 72,000 (and get, 600 amps). BUT, IF THE POWER SUPPLY IS 240 VOLTS, we divide 72,000 by 240. That comes to 300 amps, exactly half (no surprise).

What does this tell us? When you call for enough “power” to operate a space, you need to specify both “voltage” and “amperage” because what you really need to do is have enough “power” (in “watts”) to cover all of your equipment.

Some readers may want to drop off at this point, but that would be a shame. We’re going to write a little about single-phase and three-phase electrical power. We have to. That’s because while houses are usually serviced with single-phase power (whatever that is), commercial buildings are commonly hooked up to 3-phase power (whatever that is). Ruminations is willing to fend off the slings and arrows that would rightly be hurled at us by electrical engineers just so that we can try to be “simple.” We might have to write about one other wrinkle, “three-wire” versus “four-wire” service. You’ll have to press on to see if we do.

One reason large electricity using properties are served with three-phase electrical power is that the wires don’t need to be as thick. Hence, there is money to be saved. [One of its inventors is Nikola Tesla. Use the savings to buy his namesake car. It is really something special.] But, we digress. (Again, no surprise.)

The electricity you receive is “alternating” current (or “AC”). Over time (through 50 cycle service or, much, much more commonly in the United States, through 60 cycle service), the voltage in each electrical wire (say, 120 volts maximum) goes from a “plus” 120 volts to a “minus” 120 volts and back again. Yes, at the beginning, middle, and end of each cycle, the voltage passes through “zero.” [As to “plus” and “minus,” think of the two poles of a battery (the + and – poles), or think of a magnet with a “north” pole and a “south” pole, each of equal strength, but opposite in character.

In a single phase (common household) electrical circuit, the power to your light bulbs actually fluctuates (in voltage) from a peak “plus” to a “peak” minus, passing, 120 times each second, through “zero” volts. That’s too fast for you to see it happen – your eyes “average” out the lighting effect.

In a balanced three-phase (three wire) power system, this fluctuation takes place in each of the three wires. The cycles in each of the three wires “overlap” so that whatever is hooked up to the three-phase power (and is taking full advantage of the three-phase power, such as a motor) doesn’t see “zero” volts at any time (i.e., it never sees that the power is turned “off”). That’s one beauty of a “balanced” three-phase supply.

Sometimes, perhaps very often, a three-phase power supply will have a fourth wire that acts as a “neutral” (whatever that might be). Rather than go into the details (“neutral,” “wild phase,” “Delta,” or “Wye”), we’ll drill down to what comes out of the outlet.

The most common of three-phase power systems in other than power-hungry industrial buildings, are the following: (a) the older, 3-phase, 4-wire Delta 120/208/240 Wild Phase Service because you get those three voltages depending on which pair of wires you hook up to your outlets or equipment; and (b) the more common commercial service, the 3-phase, 4-wire 208Y/120V Service, which gets you 120 volts or 208 volts out of the outlets or into the equipment.

In a lot of smaller buildings (and in modern houses), you’ll see 3-wire, 240 volt, single phase electrical service. Where such service is used in a building, you get “normal” 120 volt service by connecting between one of the two “hot” wires and the “neutral, third” wire. For 240 volt service, you connect to the two “hot” wires. That will explain why, sometimes, your power will go out for only “half” of your lights. When that happens, only one of the “hot wires” went dead. Lights and outlets connected between the other “hot” wire and the “neutral” or “dead” wire will still be operating.

Let’s bookend today’s blog posting. So, instead of just calling for 600 amp electrical service, what would a more correct requirement look like? By way of example ONLY, try this:

The Leased Premises must be furnished with a dedicated 3-phase, 4-wire 208Y/120V electric service with capacity of not less than 600 amperes.

NOW, THIS IS VERY IMPORTANT. Just because you’ve reached this point in today’s posting, don’t think you can specify electrical service requirements. Though we wrote this posting, even we wouldn’t do so without help from someone who knows what might be needed. Ruminations has left out far more about electrical service requirements than it has included. We haven’t told you that large spaces often have 240/480 (or, more likely, 240/415/480) volt service, and you don’t see “120 volts” in that list. We haven’t said anything about CT Panels, distribution panels, meter boxes, and whatever.

So, just as you’d like business people to rely on us as leasing (or contract) professionals for our (supposed) special knowledge in the area, we should rely on electricians, architects, and engineers for their special knowledge in their areas. Hopefully, however, today’s posting will bridge the language gap with them when it comes to “electricity.” Remember, in the words of Albert Einstein, “A little knowledge is a dangerous thing. So is a lot.”



  1. Robert Roth says:

    In a post-Sandy world such as we have here in the New York metropolitan area this information can also be useful in writing backup power (generator, etc.) specifications.

    Ira, what is the status of DC as well as “double phase” AC? Are these even used at all any longer?

    • There is no expertise behind this answer, just my old engineering “hat” coming off the shelf, “old” being the key word. “Double phase” AC electric power is from even before your time. [For wonks], it was a supply where four wires were used, two for each phase (though it could work with three “hot” wires and one “common” wire as well). The two phases were 90 degrees apart. That will mean something to readers who understand that alternating (“AC”) power is delivered in (sine) waves). It was designed for motors that were designed for its use. Back in the early days of electric power supply, motors weren’t all self-starting. Using a multi-phase (such as a two phase) supply would make those specially designed motors “self-starting.” For uses other than those motors, one would use one pair of wires or the other. Two-phase AC power was long ago replaced by 3-phase power. My reading tells me that there are vestiges of two-phase power in some parts of Philadelphia (just as there is utility-supplied live steam available under the streets of lower Manhattan (New York City). The steam makes good sense; two-phase electric does not.

      As to DC power, some engineering historians will tell you that it wasn’t science that allowed AC power to triumph in the marketplace (the same being true for gasoline cars over electric cars), but the mighty buck being spent by industrialists. Utility supplied DC power for users is still available in limited metropolitan areas, always alongside of AC power. But, like VHS versus BETA, the equipment industry supports AC, not DC. DC power is very desirable for certain industrial applications and where that is true, users convert AC power to DC power on-site because DC power is not utility-supplied. DC power can have significant cost advantages in high voltage transmission as well and is used in places before converting it to AC power for final distribution.

      That’s all a long way of saying that ordinary retail and office users have no use for DC power or two-phase AC power coming into the building because almost every line voltage device they use is designed to be plugged into an AC outlet of either 120 volts or 240 volts.

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