In electrical theory, the answer to what is powered by electricity is formally defined as the load—any component, appliance, or device that consumes electrical energy and converts it into heat, light, motion, or data processing. The specific type of load you connect dictates the circuit's current draw, power factor, and inrush requirements, fundamentally changing how you must size your wire, breakers, and power supplies. Most DIYers and junior technicians commonly confuse a load's nominal wattage rating with its actual apparent power (Volt-Amps) draw, leading to undersized breakers that nuisance-trip or power supplies that brownout under startup surges.
The Four Core Load Profiles
Every device powered by electricity falls into one of four load categories. Understanding these profiles is the foundation of NEC-compliant circuit design and reliable DC power supply selection.
| Load Type | Phase Relationship | Power Factor | Common Examples | Sizing Gotcha |
|---|---|---|---|---|
| Resistive | Voltage & Current in phase | 1.0 (Unity) | Space heaters, incandescent bulbs, toaster coils | Draws exactly what the wattage tag says. No inrush. |
| Inductive | Current lags Voltage | 0.7 to 0.9 | AC motors, transformers, solenoids, relays | Massive inrush current (Locked Rotor Amps) at startup. |
| Capacitive | Current leads Voltage | 0.0 to 0.9 | Capacitor banks, long underground cables, flash tubes | High inrush current when initially charging empty capacitors. |
| Non-Linear | Harmonic distortion | 0.5 to 0.9 (Displacement) | LED drivers, PC power supplies, VFDs, phone chargers | Generates harmonic heat in neutral wires; requires True-RMS meters to measure. |
Worked Example: Sizing a Branch Circuit for Mixed Loads
Let's look at a real-world scenario. You are wiring a 120V, single-phase workshop branch circuit to power two devices simultaneously: a 1500W resistive space heater and a 1 HP (746W) inductive air compressor motor.
Step 1: Calculate the Resistive Load
The heater is purely resistive. Using Ohm's Law (I = P / V):
1500W / 120V = 12.5 Amps.
Because this heater will likely run for 3 hours or more, the NEC (Article 210.20) classifies it as a continuous load. We must multiply by 125%: 12.5A × 1.25 = 15.625 Amps.
Step 2: Calculate the Inductive Load
The compressor is inductive. You cannot just divide 746W by 120V (which would yield 6.2A) because you must account for motor efficiency and power factor. Instead, we use NEC Table 430.248, which dictates the Full Load Amps (FLA) for a 1 HP, 115V single-phase motor is 16 Amps. Motors are generally considered non-continuous unless specified otherwise, so we use the 16A base value for the branch circuit calculation.
Step 3: Combine and Size
Total minimum circuit ampacity = 15.625A (heater) + 16A (motor) = 31.625 Amps.
According to NEC 240.4(B), we round up to the next standard breaker size. The correct breaker is a 35A or 40A two-pole breaker (if using 240V) or a 40A single-pole breaker for 120V, paired with 8 AWG THHN copper wire (rated 50A at 75°C, safely handling the 40A protection).
Where You Meet This in Practice
Load profiling isn't just textbook theory; it dictates hardware selection on the jobsite and the workbench:
- Panel Schedules & Voltage Drop: When filling a subpanel, grouping too many non-linear loads (like LED drivers) on a single phase can cause neutral currents to exceed phase currents due to triplen harmonics. You must derate the neutral wire or use a K-rated transformer.
- Generator Sizing: A 2000W portable inverter generator can easily run a 1500W resistive heater. But it will stall and bog down if you plug in a 1500W inductive air compressor, because the generator's alternator cannot supply the 6x inrush current (9000W surge) required to start the motor's magnetic field.
- DC Power Supplies (ESP32/Arduino): When powering a 5V relay coil (inductive) directly from an ESP32 GPIO pin, the collapsing magnetic field generates a reverse voltage spike (flyback) that will instantly fry the microcontroller's silicon. You must place a 1N4007 flyback diode across the coil to clamp the spike.
Decision Tree: Selecting the Right Protection for Your Load
Use this decision path to select the exact overcurrent protection device (OCPD) for your specific load type. Do not default to standard thermal-magnetic breakers for everything.
| If Your Load Is... | And The Application Is... | Then Select This Protection Type | Concrete Part Recommendation |
|---|---|---|---|
| Purely Resistive (Heaters, Lighting) | Standard residential/commercial branch circuit | Standard Thermal-Magnetic Breaker (HACR rated) | Square D QO120CP (20A, 120/240V) |
| Inductive (Motors > 1/8 HP) | Dedicated motor branch circuit with high inrush | Motor Protection Circuit Breaker (MPCB) or Inverse-Time Breaker sized at 250% FLA | Siemens 3RV2021-1FA10 (MPCB, adjustable 3.2-4.5A) |
| Capacitive (Large capacitor banks) | Power factor correction panels | Capacitor-switching contactor with pre-insertion resistors + fuses | Schneider Electric LC1DPK12 (Capacitor Contactor) |
| Non-Linear (Server racks, LED banks) | Commercial lighting or IT panels | HID/Switching duty rated breaker with 200% neutral bus | Eaton BR2020HID (HID rated to handle harmonic heating) |
Common Confusions: Watts vs. Volt-Amps (VA)
The most frequent mistake when calculating what is powered by electricity is assuming Watts (W) and Volt-Amps (VA) are the same thing. They are only identical in purely resistive DC circuits or unity-power-factor AC circuits.
For inductive and non-linear loads, we must account for the Power Factor (PF). The formula is: VA = Watts / PF.
If you buy a 1000W (real power) LED grow light with a cheap driver that has a power factor of 0.6, the apparent power (VA) drawn from your circuit is 1000 / 0.6 = 1666 VA. At 120V, this light pulls 13.8 Amps, not the 8.3 Amps the wattage tag implies. If you put two of these on a standard 15A breaker, it will trip, even though the combined 'wattage' is only 2000W. According to Electrical Engineering Portal's guides on power quality, ignoring displacement power factor in commercial LED retrofits is the number one cause of unexplained breaker trips.
FAQ: Load Sizing and Power Supply Matching
Can I use a standard 20A breaker for a 15A inductive motor?
No. While the Full Load Amps (FLA) might be 15A, the NEC requires motor branch circuit short-circuit and ground-fault protection to be sized up to 250% of the FLA for inverse-time breakers. A 15A motor would require a 35A or 40A breaker to prevent nuisance tripping on startup, paired with a separate motor overload relay set precisely to the motor's nameplate FLA.
Why does my 12V DC power supply shut down when I connect a solenoid?
Solenoids are highly inductive. When the plunger pulls in, the inrush current can be 5 to 10 times the holding current. If your 12V DC power supply has 'hiccup mode' overcurrent protection (common in Mean Well supplies like the LRS-35-12), it will interpret the inrush as a short circuit and shut down. Fix this by adding a large electrolytic capacitor (e.g., 4700µF, 25V) across the supply output to buffer the surge, or use a supply with a constant-current limiting mode rather than hiccup mode.
Do I need to derate wires for non-linear loads like computers?
Yes, specifically the neutral wire. In a 3-phase wye system, non-linear loads generate 3rd-order harmonics that do not cancel out in the neutral; they add up. The neutral current can actually exceed the phase current. NEC 310.15(B)(5)(c) requires you to count the neutral as a current-carrying conductor for derating purposes when serving non-linear loads, and many engineers upsized the neutral to 200% of the phase wire size in data centers.
The Default Recommendation for General Purpose Sizing
If you are wiring a general-purpose 120V/240V branch circuit and the exact load profile is mixed or unknown, do not guess. Default to sizing the circuit for a continuous load (multiply the maximum expected wattage by 1.25) and use standard copper THHN wire in conduit. For a standard 20A circuit, use 12 AWG copper and a Square D QO120CP or **Homeline HOM120CP** thermal-magnetic breaker. This provides a robust, code-compliant baseline that safely handles minor inductive surges from power tools and harmonic currents from phone chargers without nuisance tripping, while maintaining strict fire safety margins.
