Point at or tap any part to see its name. Tap a heater to change its setting. Tap the drop neutral to show it whole or broken.
Amber dots show current in the wires. Red diamonds show current going back through the earth. Earth current under 0.1 A is not drawn.
The faster the dots move, the more current flows. Every wire uses the same scale. Real electrons drift far slower than a snail.
This is AC, so the current turns around 120 times a second. The dots show one half of the cycle. In the other half, every dot turns around at once.
Leg B is drawn red so you can tell the legs apart. In the field, both hots on the drop and in the mast are black. Inside, service cable often has a red leg.
The utility grounds the neutral at the transformer. That is utility practice, not NEC.
At the house, the grounding electrode conductor connects to the neutral at the service, 250.24(A)(1).
The main bonding jumper is in the service panel, the service disconnect, 250.24(C). It is not in the meter base. The meter can is usually tied to the neutral too. 250.142(A)(1) allows that on the supply side. That bond is not the main bonding jumper. After the service, neutral and ground stay apart, 250.24(B).
A metal underground water pipe is a grounding electrode, 250.52(A)(1). It needs a second electrode, here a ground rod, 250.53(D)(2). The electrodes are bonded together, 250.50.
A broken utility neutral is a failed connection, often a corroded splice or a damaged drop. No NEC section covers it. The utility repairs it.
With the neutral broken, the 240 volts split between the legs by load. The leg with less load gets more voltage. Lights flicker, and motors and electronics can be damaged.
The readouts turn red outside 114 to 126 volts, the normal range in ANSI C84.1. That is a utility standard, not code.
This is a teaching model. Each wire on the drop is 0.01 Ω, the ground rod 25 Ω, the water pipe 3 Ω to earth, and the utility's grounds 5 Ω. Real values vary a lot, so real voltages differ.
With the neutral whole, up to about 16 milliamps still go back through the earth. That is normal.
Each heater is an oil-filled heater with 600, 900, and 1500 W settings at 120 V. It is drawn as a fixed resistance, 120 × 120 ÷ watts.
The glow shows how much heat each heater makes. A real oil-filled heater does not glow.
A heater is treated as a continuous load because it can run for three hours or more. 12.5 A × 1.25 = 15.6 A, so each heater gets its own 20 A circuit, 210.20(A), on 12 AWG copper, 240.4(D)(6).
The drop is dead-ended on an insulator below the weatherhead and spliced in drip loops, 230.54(C) and 230.54(F).
AFCI protection and the cover plates are left out. The drawing is cut open and not to scale.