Volts, amps, and ohms
Voltage pushes current through a heater, and the heater's resistance holds it back. You change the voltage and the heater and watch the meters show that amps equal volts divided by ohms.
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What to try
- 1Start on 240 V with the 4 ft baseboard and note the amps. Then set Volts to 120 V. Half the voltage gives half the amps.
- 2Set Heater to 2 ft baseboard. It has twice the ohms, so it draws half the amps.
- 3Set Volts to 240 V and Heater to Water heater. Its resistance is low, so 18.75 amps flow.
NEC 2026 sections it covers
- 422.13
- A water heater counts as a continuous load.
- 424.5
- A baseboard heater counts as a continuous load.
- 210.20(A)
- A continuous load gets a breaker of at least 125% of its amps.
- 240.4(D)
- 14 and 10 AWG copper get 15 and 30 A breakers at most.
- 200.8(C)(1)
- A white wire used as a hot is re-marked with tape at both ends.
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