This page covers those mains plugs and sockets which are not in common domestic use but do not count as industrial or multiphase either.
Old Spanish sockets
Older buildings in Spain may have sockets that take a particular type of plug that has two flat contacts and a round earth pin, somewhat similar to the ones found on American plugs.
The live and neutral measure 9 mm × 2 mm × 19 mm, and are 30 mm apart. The earth pin is a cylinder with a diameter of 4.8 mm, and is 19 mm long.
While the plug may look like a USA-style connector at first glance, the spacing between the two flat contacts on this obsolete plug is much wider than found on a standard American plug. Therefore, American plugs will not fit in these sockets.
No appliances are sold with these plugs. Adaptors are necessary.
The British electric clock connector
Fused plugs and sockets of various proprietary (and non-interchangeable) types are often seen in older public buildings in the UK where they are used to feed AC electric wall clocks. They are physically smaller than conventional socket outlets, commonly being made to fit BESA junction boxes, and often of very low profile, for neatness. Early types were available fused in both poles, later types fused in the live only and provided with an earth pin. Most are equipped with a retaining screw or clip to prevent accidental disconnection. The prevalence of battery powered quartz controlled wall clocks has meant that this connector is rarely seen in new installations.
NEMA 2-15, and 2-20
These ungrounded (unearthed) plugs with two flat parallel pins are variants of the 1-15 but are intended to deliver 240 volts instead of 120. The 2-15 has both pins rotated 90 degrees from vertical and is used for 240 V service at 15 amperes, while the 2-20 has one pin rotated 90 degrees and is used for 240 V service at 20 amperes. NEMA 2 plugs and sockets are rare because they have been prohibited for household use in the United States and Canada for several decades. They are potentially hazardous since they have no ground or neutral, and in some cases plugs can be inserted into incorrect-voltage sockets. Prior to the adoption of the NEMA standard, a plug nearly identical to the 2-20 was used for 120 V at 20 A. A 2-20 plug would fit into either a 5-20 or a 6-20 socket (explained below) which use different voltages.
American "Type I" 10 A/250 V or 15 A/125 V
The American electrical supply manufacturer Hubbell, Eagle, and possibly others made outlets and plugs that would match Type I plugs and sockets exactly. Type I connectors are used in Australia for 250V. These American outlets date back to the 1930's to the early 1950's, and predated the modern American 3 prong Type B sockets and plugs. These were meant for appliances that needed grounding, 120V at 15 amps, and to be used in laundry rooms for washing machines and such. These did not become popular for the obvious reason that American type A 2 prong plugs would not fit.
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The American Type I duplex outlet, made by Hubbell -
Demo of the compatability of the American and Australian Type I plugs -
an Eagle brand adaptor to go from a 2 prong Type A outlet to a 3 prong Type I plug
Perpendicular duplex outlet, USA
Another obsolete outlet, made by Bryant, 125V 15A and 250V 10A rating. A NEMA 5-20 125V 20A or 6-20 250V 20A plug with a missing ground pin would fit this outlet. But a NEMA 2-20 plug is a little too big to fit.
The upper (as seen in the picture) slots connect to silver colored wiring screws on the upper side, and the lower (as seen in the picture) slots connect to brass colored wiring screws on the lower side .
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Combination parallel and tandem duplex outlets, USA
This is an extremely old outlet. The brand name looks to be "NURPOLIAN", and also says "250V 10A". Though it was normally supplied with 120V.
It accepts normal parallel NEMA 1-15 plugs and also tandem NEMA 2-15 plugs. Both plugs are fed internally by the same supply.
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A newer and fairly common version of this is the "T slot" outlet. The locations of the tandem and the parallel slots were combined to create the T shaped slots here. This version also accepts normal parallel NEMA 1-15 plugs and also tandem NEMA 2-15 plugs. And as in the perpendicular outlet pictured further above, a NEMA 5-20 125V 20A or 6-20 250V 20A plug with a missing ground pin would fit this outlet (as would NEMA 1-20P plugs). But a NEMA 2-20 plug is a little too big to fit. These went out of production sometime in the late 50's or early 60's.
Dormond & Smith (D&S)
The D&S plug was used by the BBC for technical supplies. The LINE pin was a fuse which unscrewed to change, unfortunately these often came unscrewed and were left in the socket, live, when the plug was removed.
Walsall Gauge 13A plug
These were also used by the BBC for technical supplies at a later date. Unlike the standard BS1363 plugs found in the UK the earth pin is on a parallel axis to the live and neutral pins
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Walsall Gauge 13A plug -
Walsall Gauge 13A plug
