Point at or tap any part to name it. Tap a receptacle to plug the drill in there.
This is a small office building. The office receptacle inside needs no GFCI. Outdoor receptacles do, 210.8(B)(6).
210.8 calls for a Class A GFCI in a readily accessible spot.
A GFCI protects its own face and anything wired to its LOAD screws. It can't see current that never passes through it.
Splicing the wires to the next receptacle onto LINE is fine when that receptacle needs no GFCI. This one is outdoors, so it needs protection.
Install a listed device the way its instructions say, 110.3(B). GFCI instructions put the feed on LINE.
Since 2006, a listed GFCI with the feed on LOAD must keep its face and LINE screws dead. Most do it by refusing to reset. The LOAD screws stay live, because the feed lands there.
Each pole has two sets of contacts, one to the face and one to the LOAD screws. When they open, the face is cut off from LOAD.
Press Test after every install (trade practice).
When you replace a receptacle that needs GFCI protection, the new one needs it too, 406.12(D)(3).
A GFCI that is off or wired wrong can still have live screws. Test before you touch (trade practice).
The drill has worn insulation, so its metal case is live. Its ground pin is broken off, so the leak goes through the person to earth. Tag the drill out until it is fixed (trade practice).
The worn spot is a poor-contact fault. The 20 A breaker carries only about 0.1 A, so it never trips.
The drill is plugged in but not running. The leak is the only current, so the red diamonds move at a speed set by the milliamps.
UL 943 sets the limits. A Class A GFCI stays on below 4 mA and shuts off at 6 mA or more. This one shuts off at 5 mA, in about 25 ms. The trip is slowed down so you can see it.
Shock effects are typical figures from OSHA, not code.
Model: 120 V, 12 AWG copper on a 20 A breaker at 1.93 Ω per 1,000 ft (Chapter 9, Table 8). 40 ft to the office receptacle, 15 ft to the GFCI, 15 ft more to the last one. 8 ft of 18 AWG cord. Worn insulation about 50 Ω from hot to case. Wet skin 1 kΩ. Earth return through a 25 Ω rod and the utility ground.
The run outdoors is in PVC conduit with separate wires and a green ground, in weatherproof boxes. NM cable is not allowed in wet or damp places, 334.12(A)(4).
Both outdoor receptacles are listed weather-resistant, 406.9(B)(1)(d). Each gets an extra-duty in-use cover, 406.9(B)(1)(a) and (b). The covers are left off the picture so the parts show.
The devices are drawn flattened, with the brass and silver screws on one edge. A real device has brass screws on one side and silver on the other.
The panel is the service, so neutral and ground are bonded there. Cut open, not to scale.