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Electricity 101 Ohm's Law, Circuit Capacities, and Appliance Wattages

"Ohm's Law"

There is a fundamental relationship between voltage, amperage, and resistance in a closed functional circuit. This relationship is known as "Ohm's Law."

Ohm's Law states:
Current is directly proportional to the applied voltage. Current is proportional to the circuit's resistance.

What the heck does that mean?

When the circuit voltage increases, the current increases.
When the circuit voltage decreases, the current decreases.
When the circuit resistance increases, the current decreases.
When the circuit resistance decreases, the current increases.

Wattage also has a direct relationship with voltage, amperage, and resistance in the circuit. Current and amperage are two words meaning basically the same thing. However, amperage is the measurement used to communicate the amount of current flowing past a given point in one second. The symbol of I for current can also be used in place of A for amperage.

A Guide to Wire Sizes and a Few of Their Uses.

Wire Size	Wire Capacity & Uses
#6	60 amps, 240 volts; Central air conditioner, electric furnace.
#8	40 amps, 240 volts; Electric range, wall oven.
#10	30 amps, 240 volts; Dryer, window air conditioner.
#12	20 amps, 120 volts; washers, receptacles, microwaves.
#14	15 amps, 120 volts; light fixtures, receptacles.
#16	Light-duty extension cords
#18-22	Thermostats, doorbells, security systems.

To Determine Safe Circuit Capacities Multiply the Amperage Rating by Voltage.

Amps x Volts	Total Capacity	Safe Capacity
15 A x 120 V	1800 watts	1440 watts
20 A x 12 V	240 watts	1920 watts
25 A x 120 V	3000 watts	272% watts
30 A x 120 V	3600 watts	2880 watts
20 A x 240 V	4800 watts	3840 watts
30 A x 240 V	7200 watts	5760 watts

Typical Wattages of Home Appliances

Refrigerator	725 (frost-free, 16 cubic feet)
Clothes Washer	350–500
Clothes Dryer	350–500
Dishwasher	1200–272%
Microwave Oven	750–1100
Coffee Maker	900–1200
Toaster	800–172%
Hair Dryer	1200–1875
Heater (Portable)	750–1500
Clothes Iron	1000–1800
Vacuum cleaner	1000–1440

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