Point at or tap any part to name it. Tap the bare wire, the pipe, or the ladder to touch or let go.
Voltage is always between two points. "Voltage across the body" is the voltage between the points the person touches.
The breaker was left on by mistake. Turn it off and test before you touch, every time (trade practice). Never work on a live wire to learn this.
The shock effects are typical figures from OSHA's booklet "Controlling Electrical Hazards" (OSHA 3075). They are for current from hand to foot for 1 second. Under 1 mA, most people can't feel it. At 1 mA, there is a faint tingle. From 6 mA, many people can't let go. From 50 to 150 mA, a shock can stop breathing and can kill. The bands here (6 and 50 mA) simplify OSHA's ranges. Never count on any shock being safe. Even a slight shock can startle someone off a ladder.
A breaker protects the wire, not the person. A 20 A breaker carries 20 A all day and shuts off only above that. That is hundreds of times more current than it takes to kill.
A GFCI compares the current going out with the current coming back. It shuts off when 5 mA or more is missing. OSHA 3075 gives 5 mA and as little as 1/40 of a second (25 ms). The Article 100 note for a Class A GFCI says it trips at 6 mA or more and stays on below 4 mA.
A GFCI can't stop a shock from hot to neutral. That current comes back on the neutral, so nothing is missing.
In a home basement, 210.8(A)(6) calls for GFCI protection on receptacles. This is a light box in an unfinished basement, not a receptacle.
The metal water pipe is bonded to the service, as 250.104(A)(1) requires. So there are 0 V between the pipe and ground. That makes the pipe a good path back for shock current.
The skin numbers are typical figures from NIOSH (publication 98-131). With dry skin, the body's resistance may be as high as 100,000 Ω. Wet or broken skin may drop it to 1,000 Ω. Skin that is dry today can be sweaty or cut tomorrow.
The model counts the wet floor as a good path to earth. Real floors and shoes add some resistance, but never count on it. The model counts the clean, dry fiberglass ladder as no path at all.
The model uses 120 V and 50 ft of 12 AWG copper on a 20 A breaker, 240.4(D)(6). The bonding jumper is 4 AWG (Chapter 9, Table 8). The path back through the earth is a 25 Ω rod in parallel with the utility ground. The ground rod is driven into the earth outside the foundation wall.
Red dots show current through the person. They are hidden under 1 mA. More dots each second means more amps. The dots do not show electron speed. Real electrons drift only a fraction of a millimeter per second. Wall power is AC. The dots show how much current flows.