Staying Safe Around Electricity At Home

Everything You Need To Know About Rheostats

by Victoria Leclercq

Rheostats are also called a variable/adjustable resistor because it is used for applications that require adjustments or different degrees of resistance in an electrical current, without disrupting the flow of the current. It is beneficial in starting or controlling motor speeds, dimming lights, or other adjustments needed in generator operations. Continue reading to learn more about how rheostats work.

How it Works

Ohm's law is the principle behind a rheostat. The current decreases as the resistance increases. Therefore, after the current goes into the rheostat, it then flows through the coil and exits. One end of the wire isn't connected to anything, and the other is connected to a live-feed wire. The third wire is a wiper that allows the current to reach its load. That is how a dimmer switch works, with the use of a rheostat.

For example, using water flow analogy, the electric current is the water running through the pipe; the resistor is the thin pipe that can limit the flow of the water. The voltage is the difference in the height of the water that can allow the water to flow.


A straight rheostat's coil is pulled straight. Space is saved with a rotary style. These units are placed in a case to protect them from elements/debris outside of the coils, such as dirt or moisture.

Composition and Uses

Rheostats can be crafted from any material allowing it to remain durable during intense changes. Depending on its application, the resistant element can be carbon, ribbon, or a metal wire. Carbon is used for smaller currents. Metal is the most common for average currents. Larger currents require an electrolytic unit where electrodes are most suitable in a conducting fluid.

A potentiometer is a special instrument/rheostat known for measuring an unknown voltage. An example of a more common potentiometer is when two fixed terminals and a third terminal are connected to a varied contact arm, like audio equipment volume control units. Other uses include as a motor speed control and light dimmers. Industries can use them with respirators, medical equipment, pumps, lamps, or fans and blowers.

Rheostats are modeled to be used with smaller currents. It will not work well with a unit such as a heater blower because the current required to reach the load would be too strong. It should not be used with anything but smaller jobs such as the dimmer switches (mentioned previously). For more information, contact professionals like those at Global Electric & Lighting Inc.