A potentiometer is a three-terminal resistor with a movable wiper. How you wire those three terminals — not the part itself — determines whether you have a voltage divider (three wires, outputs a voltage) or a rheostat (two wires, controls a current). Confusing the two is one of the most common mistakes in analog design, and it burns up more pots than any other failure mode.

Voltage divider mode (3-terminal): Connect the outer terminals across a voltage source (say +5V and GND). The wiper outputs a voltage proportional to its position, from 0V to +5V. The current through the pot is fixed by the total resistance and supply voltage — it doesn't change as you turn the knob. This is how volume knobs on audio gear, joystick position sensors, and analog input pots for microcontroller ADCs are wired. A 10kΩ pot across 5V draws a constant 0.5 mA regardless of wiper position.

Rheostat mode (2-terminal): Connect one outer terminal and the wiper in series with your load. The pot now acts as a variable resistor. Current through the load changes as you turn the knob — and critically, all of that load current flows through the wiper contact. This is how old-school motor speed controls, lamp dimmers, and current-limiting adjustments work.

Why this matters — the wiper current problem: Pot wipers are typically rated for only 100 mA or less because the contact area is tiny. In voltage divider mode, wiper current is nearly zero (it's just driving an op-amp input or ADC). In rheostat mode, the wiper carries the full load current. Turn the pot toward zero resistance while a 12V motor is drawing 2A, and you'll incinerate the wiper track in seconds.

Rule of thumb for rheostat sizing: Maximum load current should be no more than 50% of the pot's wiper rating, and the pot's power rating must exceed I²R at minimum resistance setting — because that's when current peaks. For a 1W, 100Ω pot, max safe current is √(1W/100Ω) = 100 mA at full resistance, but at 10Ω the same 100 mA only dissipates 0.1W. Always check both ends of the sweep.

Practical tip: If you need a rheostat but only have a pot, tie the unused outer terminal to the wiper. If the wiper ever loses contact (dirt, wear), the pot fails to maximum resistance instead of open circuit — the load current drops to zero instead of arcing across the gap.