Figure 7 Commentary (Compared to Fig.6 Above) New window.
11 [p-h]- Two flat (2-wire) cables at an outlet are rarely meant to do what is going on here, but maybe you should be made aware of the possibility. The white of cable-h is hot -- made hot by the black of incoming cable-p. Why? Notice that this is a receptacle whose lower half is switched by the black of cable-h (coming back here from a switch across the room). So if the room this outlet is in has no overhead light, and this half-switched receptacle is being replaced, hooking it up as if it were like receptacle-1 (without breaking the hot-side tab) would return cable-h's black's hotness (when you turned the switch on) on its white onto the neutral side, making the circuit's breaker trip immediately.
12 [p-p-h]- This one is like #11 but with an additional cable feeding the circuit out to something else. What makes receptacle-12 even rarer, though, is that the whole receptacle is being switched (found mainly in 1950s homes). More often the two-wire cable "switch loop" would be switching just half the receptacle, and a pigtail would probably used be used to join two blacks, one white, and the hot-side always-hot-half terminal. See box-13 (next).
13 [p-p-p-h]- This one adds one more outgoing p-cable and shows just one half of the receptacle being switched again. Not common either.
14 [f-f]- The more common way of switched half-receptacles is shown here. Unlike #4 above, here we have two 3-wire cables. We might like to think of one as incoming and the other outgoing, as we do with 2-wire cables. It is true that both constant and switched hot wires are receiving and/or passing on their form of hotness to another outlet box. But it can be that the black of one cable might be incoming while the red of the same cable would be outgoing! (And vice versa for the other cable.)... This would be a good place to mention something about two or more outlets of a room being switched like this. If a person replaced receptacles without regard to their being switched and then found that the switch can no longer turn a lamp off, they will not be able to solve the problem by finally breaking the hot-side tab off the receptacle they were used to using for their one lamp. The other receptacles that used to be switched (though the person didn't use them) would all need their tabs broken off too, so that blacks would not keep reds hot all the time. Either that, or the person could remove (and wirenut together) all reds from receptacles they do not want switched.
15 [p-f-f]- (Assume that this one is not a case of a double circuit doing something odd.) This demonstrates all the principles involved with #4, #5, and #14. But what is the dotted red? An outlet box that has two 3-wire cables is sometimes itself not switched at all (then the tab would still be shown in place) and the two red wires in the box would simply be wirenutted to each other and not connect to the receptacle. This would have been a convenient way to get the switching wire ultimately to a receptacle elsewhere that is the one meant to be switched. Or it might be to give the homeowner some versatility for determining which outlets (out of all that have these red wires in their boxes) will end up being switched. Different furniture layouts may call for different outlets to be switched. In answer to the question, then, the dotted red line means this could be a half-switched receptacle (with the red line solid) or it could be (if the tab were restored) an unswitched receptacle that has the potential for being switched by an added wire and the tab gone as shown.
16 [p-p-h-f]- Before reading on, you could consider this one as a midterm test: tell yourself what is going on here. ...
Right -- all the principles in #4, 5, 6, 11, 13, and 14 are happening here. Cable-h is a switch loop, so its white is given hotness, but the switched black that returns does not end the story. It passes its switchedness on to the red of cable-f. So in this example, this black should not be attached with the other black but with the red, as shown. How would you diagram a box with cables identified as p-h-f? How h-f?... It would be possible for three 2-wire and one 3-wire cables not to involve a switch loop like this (an h-cable, in other words). Such a box would have its cables identified as p-p-p-f. It would still be housing a switched receptacle. Unless, of course, it were a case of a double circuit -- along the lines of #8 or #18 (coming soon).
17 [d-d]- The double-circuit outlets common in kitchen and dining rooms of 1960s USA homes would typically pass their two circuits along together from box to box using 3-wire cable. By virtue of serving the kitchen, these would have been 12-gauge cables ("12-3"). In Canada they have been able to be 14-gauge and are still commonly installed to meet a Code requirement. In both countries neutrals needed to be pigtailed for the reason given regarding receptacle-8. Where people have replaced such receptacles without breaking off the hot-side tab, they create a 240-volt short, though they may not realize it (see Double circuit). By now Code calls for many kitchen outlets to have GFCI protection. But GFCI-type receptacles and their load receptacles can't get along with a double circuit. So when any of these "split-circuit" receptacles are replaced now, either a two-pole GFCI circuit breaker may have to be installed in the panel, or the receptacle may have to be converted to using just one circuit or the other, as illustrated somewhat in #8 and #18.
18 [d-p-p]- Here the #8 box is given an additional outgoing cable, so that both circuits continue beyond this box, not just one. This receptacle-18 is not set up to be a double-circuit (a.k.a. "split-circuit") receptacle, so no tab is broken off. The arrangement shown here is a common one for the first box that a two-circuit cable from the panel arrives at. Although all the neutrals could have been pigtailed, only two are required to be, in this case -- the shared one (in "d") arriving from the panel and the one going out with the circuit that is not connected to this receptacle. If the neutrals attached to this receptacle-18 were loose or purposely detached, the red circuit would continue to work properly and could not bother the black circuit with odd voltages. See Two-circuit cable.