If you have electrical questions you’d like answered in a future edition of this column, send them to the Editor at northshorejournal@gmail.com, or email John directly at john@clovervalleyelectric.com.
Volts, Amps, Watts, and Ohms: The Basics of Electricity
Gabe J. asked me to explain the difference between volts, amps, watts, and ohms, which may seem very basic, but is also an excellent place to start on a series of columns about how electricity gets to our homes, cabins, and businesses here in the Arrowhead region.
Volts, amps, watts, and ohms are scientific units describing different physical aspects of electricity, and they’re tied together by a set of relationships or scientific laws.
One of the easiest ways to picture volts, amps, and ohms is water in a pipe. Voltage is the pressure pushing the water through the pipe. Current is the flow rate, or how much is moving. Ohms, or resistance, is how much the pipe restricts that flow – a small-diameter pipe needs more pressure to push a given flow rate through it than a large-diameter pipe does. Volts, amps, and ohms are related through Ohm’s Law, which says that voltage equals amps times ohms. So, if a household circuit operating at 120 volts has 10 ohms of load, the circuit should have 12 amps flowing on the conductors.
Watts combine voltage and amperage. The watt is the electrical unit of power, which is the rate at which electrical energy is actually doing work. An electric space heater might pull about 1,500 watts – 120 volts times 12.5 amps. A dryer can pull far more power when operating at a higher voltage – 240 volts at about 22.5 amps is 5,400 watts. When a higher voltage is used on a circuit, the same amount of power can be delivered with lower current, and lower current is easier on wires and connections because the interaction of current and resistance creates heat. This relationship – pushing the voltage up to bring the current down – is how the electrical grid transmits power across long distances, which is a discussion I’ll get to later this summer.
Here’s the part most people rarely explore outside of a physics class. In an alternating-current system, voltage and current don’t hold steady over time. They rise and fall many times a second – roughly 60 cycles per second in America – creating a wave shape when viewed over time. When those two waves rise and fall together, in step with each other, every watt of the electricity does useful work. But some equipment – anything with a motor or a coil of wire, such as a well pump, a fridge compressor, or a transformer – pulls the current wave out of alignment. When they’re out of alignment, some of the electricity “sloshes” back and forth without doing any work. That sloshing takes up capacity on the wires, like water partially filling a pipe but never reaching the far end. We measure the out-of-alignment electricity separately, in a unit called VARs.
A glass of beer is the analogy normally used here. The liquid beer is the real power – the part you drink and use. The foam is the sloshing, out-of-step part: it’s still beer, but it fills space in the glass without giving you much to drink. The ratio of liquid beer to the whole pour is what engineers call power factor. A glass that’s nearly all liquid has a power factor near one, which is what you want, and a foamy one has a poor power factor. I’ll have more to say about power factor in a future column on how electrical energy is delivered across the grid.
The last fundamental unit of electricity is energy, which is what your bill reflects. Electric bills report kilowatt-hours used — basically 1,000 watts running for one hour. That 1,500-watt space heater running for exactly one hour uses 1.5 kilowatt-hours. When electricity is priced at 10 cents per kilowatt-hour, the heater costs 15 cents an hour to run. If it runs for a full week (168 hours), it adds around $25 to your bill that month.
So that’s the foundation of electricity: pressure (voltage), flow (current), and resistance (ohms) describe electricity in a pipe while watts, VARs, and power factor describe how it behaves when doing “work” as alternating current in our homes, cabins, and businesses. Next time, I will walk through how these units describe the transmission and distribution of electrical energy from the generator to the meter.
John Christensen is a licensed Master Electrician in Minnesota and has a bachelor’s degree in electrical engineering from the University of Minnesota – Duluth. If you have electrical questions you’d like answered in a future edition of this column, send them to the editor, or email John directly at john@clovervalleyelectric.com
The advice provided in this column is intended for general informational purposes only. If you have specific concerns or a situation requiring professional assistance, you should consult with a qualified professional for advice or service tailored to your individual circumstances. The author, this newspaper, and publisher are not responsible for the outcomes or results of following any advice from this column. You are solely responsible for your actions.
