What Is an Inductive Load, and How Does It Relate to RMS?
An inductive load is any component in an electrical circuit that creates a magnetic field when current flows through it. Motors, transformers, solenoids, and compressor windings are all common examples, anything that relies on electromagnetism to do its job.
How Does an Inductive Load Affect Current and Voltage?
When alternating current (AC) flows through an inductive load, the fluctuating magnetic field generates a voltage that opposes the current, called back electromotive force (EMF). This opposition causes the current to lag behind the voltage, the amount of lag depends on how much inductance is in the load. This lag is a real, measurable effect, and it’s the reason a motor draws more apparent power than the actual work it’s doing would suggest.
What Is RMS, and Why Does It Matter Here?
RMS (root mean square) is a way of expressing the effective value of an AC waveform, calculated by squaring the instantaneous values, averaging them over one cycle, and taking the square root. For any sinusoidal waveform, RMS is naturally higher than the simple average, that’s true whether the load is resistive, inductive, or capacitive, it’s a property of the math, not something the inductance itself causes.
What inductance does change is the relationship between voltage and current, the phase lag we just covered. That lag creates a gap between the power a circuit appears to draw (apparent power) and the power it actually uses to do work (real power). The ratio between the two is called the power factor, and it’s a genuine efficiency concern: a low power factor means a motor or compressor is pulling more current from the panel than its actual output would suggest, which matters for wire sizing, breaker selection, and utility billing on commercial accounts.
Why This Matters on the Job
For techs and electricians, this isn’t just theory. Motor starting current is a real-world example, an AC motor can briefly draw several times its running current the instant it starts, largely due to this same inductive lag, which is why motor circuits need breakers and wire sized for that inrush, not just steady-state draw. Capacitor sizing on HVAC compressors exists specifically to correct power factor and reduce that inrush penalty. Getting inductance right isn’t academic, it shows up directly in equipment selection, panel capacity, and callback-worthy mistakes if it’s ignored.
The Discovery of Inductance
Inductance was uncovered independently by two scientists working an ocean apart in the early 1830s. Joseph Henry, an American physicist, observed the effect in 1830 but didn’t publish his findings right away. Michael Faraday, working in England, demonstrated electromagnetic induction and published his results in 1831, earning him credit as the first to publish. Henry continued his own research and published his findings on self-induction in 1832, work significant enough that the standard unit of inductance, the henry (H), is named after him. Both men are considered foundational figures in electromagnetism, and their work laid the groundwork for the motors, transformers, and solenoids technicians work with every day.
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About the Author, James R. Leichter
James is a successful entrepreneur and master mechanic widely referred to as Mr. HVAC. His accomplishments include being the CEO and founder of Aptora, the President of RA Tax and Accounting, the founder of MrHVAC.com, and a partner with Pro-American Investments. He is also the creator of Flat Rate Plus®, which is hosted on this flatratesoftware.com website.
James is well known for his burning passion to help contractors and it shows in his unique speaking style. His articles have been widely published by the industry’s most popular magazines. His videos have had over one million views. James has hosted management workshops all around the United States and has conducted onsite consulting with hundreds of contractors.