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If the local times of two places differ by one hour, the difference in longitude between them is 15° (360°/24h). Before telegraphy, absolute time could be obtained from astronomical events, such as eclipses, occultations or lunar distances, or by transporting an accurate clock (a chronometer) from one location to the other. The FCC required operators to black out programming that comes in from distant markets and duplicates a local station’s own programming (if the local station demanded it). What had been the accepted norms for the industry for sometimes, 80 years, have suddenly been thrown out and replaced by fundamental changes in design, manufacture and operation. This "2-prong" design, with two flat parallel non-coplanar blades and slots, is used in most of North America and on the east coast of South America on lamps; consumer electronics such as clocks, radios, and battery chargers; and other double-insulated small appliances that do not require grounding (earthing). Surge protective devices are designed to reduce the random energy surges of voltage transients and electrical noise on the power supply line, which can damage sensitive electronics such as TVs, computers, what is electric cable and smart appliances. However, they can usually charge Type 1 as well.

Newer NEMA 1-15 plugs with wider protective faces (middle right) have a safety advantage; plugs for electric toys (right) as well as very early plugs (left) have noticeably wide faces to discourage touching the electrical contacts. A NEMA 1 cord from 1932, with wide protective face to prevent touching the electrical contacts. The 50 A (and 5-50) receptacles look like bigger versions of the 5-15 A. 6-15R and 6-20R receptacles are usually manufactured on the same assembly line as "Industrial" or "Commercial" grade 5-15R and 5-20R receptacles, with all 4 receptacles sharing the same "triple wipe" T contacts behind the varying faceplates. All NEMA 5 devices are three-wire grounding devices (hot-neutral-ground) rated for 125 V maximum, with the 5-15, 5-20 and 5-30 being grounded versions of the 1-15, 1-20 and 1-30, respectively. Polarized 1-15P plugs will fit 5-15R grounded receptacles, which have the same wider slot for the neutral blade. There are no 1-20R and 1-30R receptacles, because 1-20P and 1-30P can mate with a corresponding NEMA 5 receptacle. The plugs can be detached from the receptacles by pulling back on the plug body.

Many plugs manufactured since 1948 are polarized; the neutral blade is 5⁄16 in or 7.9 mm wide, 1⁄16 in or 1.6 mm wider than the line blade, so the plug can be inserted only one way. Between the 1890s and the 1930s, line work was considered one of the most hazardous jobs. In the late 1880s and early 1890s smaller electric companies merged into larger corporations such as Ganz and AEG in Europe and General Electric and Westinghouse Electric in the US. Electric toothbrushes in the UK are normally supplied with the same plug. In older plug designs both blades were the same width, so the plug could be inserted into the receptacle either way around. This plug was also once used in theatrical installations for the same reasons as the 15 A model below. Internationally, the NEMA 5-15P plug and NEMA 5-15R receptacle are the basis for the International Electrotechnical Commission's IEC 60906-2 standard IEC system of plugs and sockets-outlets for household and similar purposes - Part 2: Plugs and socket-outlets 15 A 125 V a.c.

The neutral blade on 5-15P plugs is not always wider than the line blade, since the ground pin enforces polarity. When the ground blade of a receptacle is on the bottom, the neutral blade is on the upper left and the hot blade is on the upper right. One blade is wider on a polarized 1-15P plug. One approach was to have resonators of several different frequencies act as carriers of a modulated on-off signal. These tasks may have to be performed with primitive manual tools where accessibility is limited. It is usually installed in a duplex configuration; two receptacles may share a common circuit or may each be wired separately, sometimes to a switch. Replacement of obsolete NEMA 1 receptacles requires either rewiring with an additional ground conductor for a NEMA 5 receptacle, or a NEMA 5 receptacle complete with a ground fault circuit interrupter for two-wire non-grounded configurations (when a ground conductor is not available). This is accomplished by an interlocking mechanism that requires hot and neutral blades inserted simultaneously to release the small doors blocking the slots. The blades of a NEMA connector are identified within the dimensional standard as follows: 'G' identifies the grounding conductor, 'W' identifies the (grounded) neutral conductor, and 'X', 'Y', and 'Z' are the "hot" line conductors.