Thanks for the info on the "Clix" stacking plugs. We never had the inclination to investigate the insides of the plugs as we were too busy with our experiments.
I have posted some more examples of the use of “Lights” and “Amps” to describe current ratings. The installation costs estimates use “Lights” for the switches and “Amp” for the cut-outs. The installations are for a 50V DC supply voltage using 16CP lamps which, as has been observed, did consume about 1 Amp, so on a 50V system, 1 Light did mean 1 Amp. Perhaps 50V was preferred for private lighting systems before public electricity supplies became widely available.
Re Hubbell's plug, the date of 1904 that is given on the Wikipedia's AC plugs site seems to be based on information that used to appear on the Hubbell web site but has since been removed. The earliest Hubbell patent I have found that illustrates something like the present US flat pin plug configuration is US 1,064,833 that was filed on Jan 2, 1912, but it has detents in the
edges of the pins rather than the central holes that are still found on some US plugs.
The drawings of both US 783,275 of 1904 shown on Wikipedia, and US 776,326, filed by Hubbell on the same date, clearly show round pin plugs of the European pattern. Hubbell’s invention lay in the provision of jackplug-like detents in the ends of the prongs to prevent the plug from falling out of the adopter when hanging from a pendant lampholder. US 776326 "Multiple attachment plug" is possibly the first multi-way adapter. Its Fig 4 shows a 3 way socket adopter for the round pin latching plugs, plugged into what is described as "a receptacle of any ordinary type" that seems from the drawings to consist of a square insulating plug having two contact strips on opposite faces: think of a square Schuko plug with no pins where the earth strips are as wide as the sides and are used as the two contacts. Hubbell did patent a flat pin latching plug in 1905, US 793,197, but the pins lay in the same plane like a UK BS1363 plug; a polarised 2 pin plug with two flat pins oriented at right angles [as was/is used in New Zealand?] ; and in his patent US923,179 of 1909, a plug with parallel flat pins similar to the present US pattern, but with the pins shaped like sugar tongs to provide latching detents.
US 1,064,833 can be viewed at the EPO’s Espace web site at the following link:
http://worldwide.espacenet.com/publi...m&locale=en_EP
US 776, 326 here:
http://worldwide.espacenet.com/publi...m&locale=en_EP