understanding electricity for portable generators benjamin-franklinDo you recognize this man?  I’d ask you to look on a hundred dollar bill, but if you’re like me, you don’t have one lying around.  Well it’s Ben Franklin.  Remember him and his kite and his key in the lightning storm?  Well from lightning to the shock that you’d give your sister after rubbing your feet on the rug, we know it’s there but don’t know much about it.

But now you’ve purchased a portable generator or are thinking about it.  You want an understanding of electricity for portable generators to get the most use out of one, but also to operate it safely.  You know that a motor turns mechanical energy into electrical energy (read “How a Portable Generator Works” on this site).  You see receptacles on the power panel.  Some look simple enough – like the ones on your kitchen walls.  But some larger models have some funny looking power outlets. For a general review of some typical outlets and necessary power cords, check out the article on extension cords on this site.

You might be confused by the designations on the power panel like 120V/240V, 30A, 60Hz and the model number is based on its watts.  You want at least enough knowledge to know how to safely use a portable generator.  You will not be a certified electrician after reading this (nor am I), but you will gain a basic knowledge of electricity whether supplied by your power company or by your portable generator.

Understanding Electricity for Portable Generators

Direct Current (DC)

The simplest way to look at Direct Current (DC) is to look at your standard battery that you use to power your flashlight or remote control device.  You notice that there is a positive end or terminal (+) and a negative end (-).  Current always wants to flow from the positive end to the negative end.  When the two ends are connected, usually with a copper wire or some other conductor, a circuit is formed.  Negatively charged electrons in the wire can then flow from the negative end to the positive terminal.

The source of electricity (whether it is a generator, battery or something else) will want to push electrons out of its negative terminal at a certain voltage. For example, one AA battery typically wants to push electrons out at 1.5 volts.

light bulb currentMoving electrons have energy.  The flow of electrons is called in this case is called a current.  If a load such as a light bulb or motor is connected between the terminals and connected to the wire, the electrons flow through the bulb or motor and make it do its thing – light up or spin a shaft.  You might think of it as water flowing and turning a paddle wheel along the way.  To get scientific for a moment, in a light bulb, the electrons produce heat in the filament which creates light.  In the motor, the electrons create a magnetic field, which interacts with other magnets (attraction and repulsion) to create motion.

Many portable generators have an outlet to supply 12 volt direct current for uses such as charging your car battery.  All portable inverter generators have DC outlets.  For more information, you can read our article about inverter generators.

Electrical circuits can get quite complex, but basically you always have the source of electricity (such as a battery), a load and two wires to carry electricity between the two. Electrons move from the source, through the load and back to the source.

Alternating Current (AC)

wall outlet standardAlternating Current (AC) differs from Direct Current (DC) in that the direction of the current reverses, or alternates, 60 times per second (in the U.S.) or 50 times per second (in Europe, for example). This is where the 60 in 60Hz or 60 cycle electrical power comes from.  The power that is available at a wall socket in the United States is 120-volt, 60-cycle AC power.

The power grid which supplies power to our homes needs AC, because it is relatively easy to change the voltage of the power, using a device called a transformer. Power companies use very high voltages to transmit power over long distances and eventually to your home.

To illustrate, let’s say that you have a power plant that can produce 1 million watts of power. One way to transmit that power would be to send 1 million amps (Amps is a measurement of current flow) at 1 volt. Another way is to transmit 1 amp at 1 million volts. Sending 1 amp requires only a thin wire, and not much of the power is lost to heat during transmission. Conversely, sending 1 million amps would require a huge wire.  Power companies convert alternating current to very high voltages for transmission (such as 1 million volts), then drop it back down to lower voltages for distribution (such as 1,000 volts), and finally down to 120 volts inside the house for safety.  Read on for a simpler version of how voltage and amperage relate.

Most portable generators produce 120 volts or a combination of 120 volts and 240 volts, and up to 50 Amps.  the most common provide from 1000 watts up to 10,000 watts.

Voltage, Current and Resistance

As mentioned earlier, the number of electrons in motion in a circuit is called the current, and it’s measured in amps. The “pressure” pushing the electrons along is called the voltage and is measured in volts.

To better visualize this, think of a tank of pressurized water connected to a hose that you’re using to wash your car. If you increase the pressure in the tank, more water comes out of the hose, right? The same is true of an electrical system: Increasing the voltage (water pressure) will result in greater current flow through the same wire.

understanding electricity for portable generators water hose analogy

If you know the amps and volts involved, you can determine the amount of electricity consumed, measured in watts.  There is a mathematical relationship between the three:

Watts = Volts x Amps

We know that our standard wall outlet supplies 120 volts.  If our electrical device draws ½ Amp, then 120 volts x ½ Amp = 60 watts.  And you guessed it, a 60 watt light bulb draws ½ Amp.  Think of a 1200 watt hair dryer.  Simple math tells you that it draws 10 Amps.

Now let’s add one more factor to current and voltage: resistance, which is measured in ohms. We can extend the water analogy to understand resistance, too. The voltage is equivalent to the water pressure, the current is equivalent to the flow rate and the resistance is like the hose diameter.

Now say you increase the diameter of the hose and all of the tank’s fittings. This adjustment would also make more water come out of the hose. This is like decreasing the resistance in an electrical system, which increases the current flow (like a greater diameter wire).  We can measure this water flow in volume per second, while electrons flowing in a current we measure in Amps.

When you look at a normal incandescent light bulb, you can see this water analogy in action. The filament of a light bulb is an extremely thin wire. This thin wire resists the flow of electrons. The resistance causes heat and then light.

Confused yet?  Read on for more applicable knowledge for using your portable generator.

Electrical Ground

We can’t talk about electricity basics and their relation to portable generators without a discussion on electrical grounding, or just ground. For example, an electrical generator will say, “Be sure to attach to an earth ground before using.”

The planet is a good grounding conductor, and it’s huge, so it makes a handy return path for electrons. “Ground” in the power-distribution grid and referenced in the portable generator recommendation is literally the ground that you walk on.

Every utility pole on the planet has a bare wire stapled in a coil to the base of the pole as a ground. That coil is in direct contact with the earth once the pole is installed, and is buried 6 to 10 feet (2 to 3 meters) underground.

Similarly, near the power meter in your house or apartment there is a 6-foot (2-meter) long copper rod driven into the ground. The ground plugs and all the neutral plugs of every outlet in your house connect to this rod. This is to reduce the chance of your coming in contact with the voltage flowing through a hot lead (pronounced leed not led) wire.

Portable generator manuals recommending attaching a ground wire from its grounding terminal to a rod driven into the ground whenever you operate it.  Whereas most people rely on the bonded neutral ground to its frame in a portable generator, when attaching a portable generator to your home’s power, an electrician will always connect to your homes ground.

Grounding Plugs – Why?

SONY DSCThree-prong plugs help guard against electric shock.

­Let’s start with what the holes in an outlet do. When you look at a normal 120-volt outlet in the United States, there are two vertical slots and then a round hole centered below them. The left slot is slightly larger than the right. The left slot is called “neutral,” the right slot is called “hot” and the hole below them is called “ground.” The prongs on a plug fit into these slots in the outlet.

Remember in a battery, electricity flows from one terminal of the battery to the other. In a house outlet, power flows from hot to neutral. The appliance you plug into an outlet completes the circuit from the hot slot to the neutral slot, and electricity flows through the appliance to run a motor, heat some coils or whatever. Let’s say you plug a light bulb into the outlet. The power will flow from the hot prong, through the filament and back to the neutral prong, creating light in the process.

What if you were to directly connect the hot slot to the neutral slot of an outlet?  Like say with a single thick copper wire.  Unlike an appliance, which limits the amount of electricity that can flow to 60 watts (for a light bulb) or 1200 watts (for a hair dryer) the wire would let an incredible amount of electricity flow through it. Back in the breaker box, the circuit breaker for the outlet would detect this huge surge and it would cut off the flow of electricity. The circuit breaker prevents the wires in the wall or the outlet itself from overheating and starting a fire.

The ground slot and the neutral slot of an outlet are identical. That is, if you go back to the breaker box, you will find that the neutral and ground wires from all of the outlets go to the same place. They all connect to ground. Since they both go to the same place, why do you need both?

If you look around your house, what you will find is that just about every appliance with a metal case has a three-prong outlet. The metal casing is connected directly to the ground prong wire.  This is for your protection.

Let’s say that a wire comes loose inside an ungrounded metal case, and the loose wire touches the metal case. If the loose wire is hot, then the metal case is now hot, and anyone who touches it will get a potentially fatal shock. With the case grounded, the electricity from the loose hot wire flows straight to ground, and this trips the breaker in the breaker box. Now the appliance won’t work, but it won’t kill you either.

Wrap Up and Disclaimer

Well, that should give you a pretty basic overview of electricity and how it relates to your use of a portable generator.  This is BY NO MEANS a comprehensive review of electricity.  Do NOT use the information to perform any work or repairs that are better left to a qualified electrician.

If you’re like me, you like to know how things work.  You get a good start here.  But for more extensive information or to confirm what you read here, do your due diligence and satisfy your knowledge accordingly.

Filed under: Understanding Electricity