Electrical · Smart Grid & Energy Management
Residential Load Profile & Peak Demand Study
Log a continuous 24-hour power trace of a real household with a clamp-on current sensor, then do what a distribution planner does with it: find the peak, compute daily kilowatt-hours, measure the coincidence factor between appliances, and calculate the load factor. This is the single most transferable project on this site for anyone who wants to work at a utility.
Safety: Use an AC line splitter so the clamp goes around one conductor that is already separated for you. Never cut, strip, or open a live cord to get at a single conductor, and never open your electrical panel.
Major
Electrical
Focus area
Smart Grid & Energy Management
Total hours
10-15 hours
Why this project matters
Every utility in the country runs on this analysis. Before anyone builds a substation, upgrades a transformer, or approves a new subdivision, someone opens a load profile and answers the same questions you are answering here: when does this thing peak, how much energy does it move in a day, and how hard is the equipment working relative to its rating.
Most students who apply to utilities have never seen a load profile. If you can open one, read it, and say something intelligent about load factor and diversity, you are already ahead of most entry-level candidates, and you did it with about $60 of parts and a weekend.
The numbers you compute here also carry straight into building energy auditing, data center capacity planning, EV charging infrastructure, and anything else where someone has to size equipment for a load that moves.
How it works
A clamp-on current transformer works without touching the conductor. Current flowing through a wire creates a magnetic field around it, and the split core clamped around that wire turns the field back into a small current in the sensor's winding, proportional to what the wire is carrying. A burden resistor turns that small current into a voltage your microcontroller can read.
The catch is that it has to be one conductor. A normal appliance cord carries hot and neutral side by side, flowing in opposite directions. Clamp around the whole cord and the two fields cancel almost perfectly, so you read nothing. An AC line splitter solves this by separating the conductors into a loop you can safely clamp, with the insulation never opened.
Current alone is not power. You are measuring amps, and power is volts times amps times power factor. For a rough audit, assuming 120 volts and a power factor near 1 is fine for resistive loads like heaters, kettles, and incandescent bulbs. Motors and switching power supplies have power factors well below 1, so your number will read high for those. Say so in your write-up. Naming the limitation is what separates an engineering report from a science fair poster.
Once you have power numbers you trust, the first thing anyone at a utility asks for is load factor: average demand divided by peak demand over the same window. A house sitting at 0.3 is drawing, on average, only 30 percent of what its peak forces the system to supply. That gap is the whole headache of utility planning, because the grid gets built for the peak and then sits mostly idle.
Then comes the number that surprises people. Add up the peak draw of your fridge, your microwave, your dryer, and your AC and you will get something far bigger than the peak you actually measured, because those things almost never fire at the same moment. Divide the measured group peak by the sum of the individual peaks and you have the coincidence factor. It is why a transformer serving 10 houses never gets sized for 10 times one house peak.
What you'll need
- ESP32 development board (or Arduino Nano)
- SCT-013-030 clamp-on AC current sensor
- AC line splitter with a separated conductor loop
- 33 ohm burden resistor and 10uF capacitor (if your sensor has no built-in burden)
- 3.5mm audio jack breakout board
- Breadboard, jumper wires, and a USB cable
Steps
- Plug the AC line splitter into the wall and the appliance into the splitter, then clamp the sensor around the separated single-conductor loop. Do not modify any cord.
- Wire the sensor through the burden resistor into an analog input and confirm you read near zero with nothing running, then a sensible value with a known load like a 60 W bulb.
- Calibrate against something you can verify. A resistive load with a printed wattage is the easiest check, and your reading should land within about 10 percent.
- Log whole-house or whole-circuit current every 10 to 60 seconds for a full 24 hours, including an overnight window, and write each sample with a timestamp.
- Separately, measure each major appliance's own peak draw: fridge, microwave, AC or space heater, dryer, electric kettle, whatever you have.
- Convert current to power, then integrate over time to get kilowatt-hours for the day.
- Find your peak demand, then compute load factor as average demand divided by peak demand.
- Compute coincidence factor as your measured whole-house peak divided by the sum of the individual appliance peaks, and explain the gap.
- Zoom into the 2 to 5 a.m. window, identify your baseload, and hunt down what is drawing it.
- Write up the profile, the four numbers, and what you found overnight.
What usually goes wrong
Clamping the sensor around a whole two-conductor appliance cord and reading almost zero.
Do this instead: Use an AC line splitter. The hot and neutral in a normal cord carry equal and opposite current, so their magnetic fields cancel and the clamp sees nothing. The splitter separates one conductor into a loop you can clamp without ever opening insulation. If your reading is suspiciously near zero, this is why, every time.
Sampling too slowly and missing the peak entirely.
Do this instead: Log at least every 60 seconds, and every 10 seconds if you can. A microwave runs for 90 seconds. A well pump might run for 40. Sample every 5 minutes and you will walk right past the event that sets your peak, then report a peak demand that is quietly wrong.
Mixing up energy and demand.
Do this instead: Energy is kilowatt-hours, which is what your utility bill charges you for. Demand is kilowatts, the instantaneous rate, which is what the equipment has to survive. A space heater running all night uses far more energy than a microwave, but the microwave may set your peak demand. Residential customers usually pay for energy. Commercial customers pay for both, and that is exactly why demand matters.
Reporting apparent power as if it were real power.
Do this instead: You are measuring current and assuming voltage. For motor loads and electronics, the actual power is lower than amps times volts because the power factor is below 1. Either state the assumption clearly in your write-up or, if you want to do it properly, add a voltage sensing channel and compute real power from the instantaneous product of the two.
Logging only one circuit and calling it the house.
Do this instead: A single outlet is a single outlet. If you are only clamping one appliance, say so and call it an appliance profile. If you want a true whole-house profile, you need to measure at the service entrance, which means a licensed electrician, not a student with a breadboard. Scope honestly and the project is still strong.
From the field
When I open a raw 24-hour load profile, I am not really looking at the big afternoon peak. Everyone sees that. I am looking for baseload creep and unexpected thermal cycling.
The moment that makes me pause and say huh is usually discovering that a home's baseline draw at 3:00 a.m., with everyone asleep, is 800 watts. Then the hunt starts. Is it an old crawlspace dehumidifier running continuously? A pool pump on an improper timer? A refrigerator with a defrost heater stuck in a cycling loop?
In distribution planning, that hidden baseline tells you more about system stress and chronic energy waste than the obvious peak ever will. So when you do this project, do not just chart your peak. Go hunting at 3 a.m. and find out what is still awake.
Your Engineering Sister, PE (Electrical: Power), distribution planning
What to photograph for your portfolio
- The full 24-hour load profile chart with the peak hour labeled
- A bar chart of each appliance's individual peak next to the measured whole-house peak
- The clamp on the line splitter, showing the safe single-conductor loop
- Your load factor and coincidence factor calculations written out
- The overnight baseload window zoomed in, with the mystery load called out
Resume bullet starters
Copy one, then swap in your own numbers.
Instrumented a residential service with a clamp-on current sensor to capture a continuous 24-hour load profile at [insert your sampling interval]
Calculated daily energy consumption, peak demand, load factor, and coincidence factor, finding a coincidence factor of [insert your result] across [number] measured appliances
Identified [insert your result, such as a 300 W continuous overnight baseload] and quantified its annual energy cost at [insert your number]
If this is on your resume, expect to be asked
You measured a whole-house peak of 4.5 kW, but when you added up the peak draws of your individual appliances you got 11 kW. Why can't a utility just sum the peak nameplate ratings when sizing a neighborhood transformer, and how did your coincidence factor calculation prove it?
What they're listening for: Not textbook definitions. They want to hear that appliances never fire simultaneously because of human behavior and duty cycles, which is diversity, and that the practical consequence cuts both ways: underestimate it and you undersize grid assets and burn them up, overestimate it and you waste capital on equipment that never gets used.
What was your sampling interval, and how do you know it was fast enough?
What they're listening for: Whether you thought about the shortest load event you cared about catching and picked an interval under it. A candidate who says 'every 5 minutes' without flinching has not thought about what a microwave does.
What is your biggest source of measurement error?
What they're listening for: The power factor assumption, almost always. Knowing where your own number is weak is more impressive than a clean number you cannot defend.
Take it further
- Add a voltage sensing channel and compute real power and power factor instead of assuming them.
- Log for a full week and compare a weekday profile against a weekend one.
- Get two or three friends to run the same logger, then compute the coincidence factor across households rather than across appliances. That is the number a planner actually uses.
- Overlay your local utility's time-of-use rate periods on your profile and calculate what shifting your dryer would save per year.
- Repeat in summer and winter and compare how much of your peak is weather-driven.