120 and 240 volts
One coil on the pole feeds a home two hot legs that mirror each other. You move a meter between the wires and watch why one hot to the neutral reads 120 V and hot to hot reads 240 V.
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What to try
- 1On Wired right, set Meter across to A to N, then to A to B. One leg to the neutral reads 120 V. Leg to leg reads 240 V.
- 2Set Leg A to Lamp and Leg B to Toaster. The neutral carries only the difference between the two.
- 3Pick Heater on one leg and set Meter across to Heater. Both heater wires are on leg A, so it reads 0 V.
NEC 2026 sections it covers
- 120.5(A)
- 120/240 V is a nominal system voltage.
- 250.26
- The neutral is the wire that gets grounded.
- 250.24(C)
- The neutral and the panel are tied together at the service.
- 250.24(B)
- The neutral is not bonded again past the service.
- 250.53(A)(2)
- One ground rod usually needs a second electrode.
- 200.8(C)(1)
- A white wire used as a hot is re-marked with tape at both ends.
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
More visuals
- Switch the hotWires are colored by voltage. See why a light can be off and still live.
- From the pole to the panelThe transformer on the pole sends two hots and a neutral to the house. Break the neutral and watch the voltages split.
- Three-phase powerA three-phase panel has three hots, each a third of a cycle apart. Two hots read 208 volts, not 240.