Why voltage drops
Every foot of wire has a little resistance, so the wire acts like a small resistor in series with the heater. You change the length, the wire size, and the load and watch the volts lost on the way.
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What to try
- 1Start on 25 ft with the 1,000 W heater. The heater gets nearly the full 120 volts.
- 2Set Length to 200 ft. The wire now loses far more voltage and turns it into heat.
- 3Keep 200 ft and set Wire size to 10 AWG. Thicker wire has less resistance, so the heater gets more of the voltage.
NEC 2026 sections it covers
- 210.19
- An informational note suggests losing no more than 3% on a branch circuit.
- 215.4(A)(2)
- With the feeder counted too, the target is 5%.
- 90.5(C)
- Informational notes are advice, not rules.
- 240.4(D)
- 14 AWG copper gets a 15 A breaker at most.
- 250.122(D)
- When the hots are made bigger for voltage drop, the ground gets bigger too.
- 424.19(B)(1)
- A breaker that is the heater's shutoff must lock off when it is out of sight.
- 110.29
- In sight means you can see it and it is 50 ft away or less.
- 210.12(B)
- Many rooms in a home also need AFCI protection.
Section numbers only. Read the full text in your code book. Temperatures and times in the visual are teaching models.
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Practice it and teach it
- Voltage Drop simulationStretch a run across the yard and watch the lamp dim, then size the wire to keep the drop in spec.
- Voltage drop lessonVoltage drop (NEC 2026 informational notes and Chapter 9, Table 8)
More visuals
- A circuit is a loopCurrent flows only when it has a full path out and back. Open the switch or break a wire and watch it stop.
- Conductors and insulatorsPut copper, aluminum, rubber, or skin on the meter and see how hard each one makes it for current to get through.
- Volts, amps, and ohmsChange the voltage or the heater and watch the amps follow. Amps equal volts divided by ohms.