Information and photos of several old electrical hardware items of the variety used in the US, plus a small amount of information about historic aspects of electrical power distribution (AC versus DC.)
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In the early days of electrical power distribution in the US, there was a "war of the currents" over the promotion and adoption of AC versus DC. Thomas Edison had a preference for DC over AC, even though AC later became almost exclusive. At the same time, DC was not unknown even in the mid 20th century. Author Robert Claiborne mentioned New York's Greenwich Village in 1942 as being a neighborhood that used DC, and noted that appliances would be labeled to indicate whether they worked with AC, DC, or both. In the 1940s, there were locations where the Consolidated Edison power company offered both AC and DC power, often with the configuration where both AC and DC went into the same building and were supplied to the same types of receptacles. The Waldorf-Astoria Hotel in New York had separate supplies for AC and DC and some of its receptacles were fed with DC. Up into the 1960s, the city of Boston used 110 volts DC in a small area near to Boston University.
The photo below shows an electrical switch of a variety that is intended for use with fixed wiring. The switch was made by the GE Co. (General Electric Company) and has an indicated rating of 5 amps at 250 volts or 10 amps at 125 volts. When turned on or off, the switch makes a noticeable "click." Unlike many modern switches, this switch does not appear to be marked "AC only" or specifically marked with regard to AC. This indicates an AC/DC general use switch that can be used with AC (alternating current) or with DC (direct current) under certain circumstances.
View larger image (AC/DC switch; 328KB)
The continuous nature of DC causes more severe arcing across switch contacts when a switch is being turned on or off; an "AC only" switch is not designed to deal with this increased arcing. An AC/DC general use snap (toggle) switch can be used to control a resistive load (such as a heating element) or an inductive load (such as a fluorescent light or a transformer-based power supply) and if the switch has a horsepower rating it can be used to control electric motors. If an AC/DC general use switch is marked as being "T-rated" (this is not the case for the previously depicted GE Co. switch) it can be used to control a tungsten filament lightbulb.
The photo below shows a Slater brand switch that appears to have the letter "T" stamped on the metal bracket to the left of the upper-left gold-colored screw. This indicates a "T rated" switch (see the previous paragraph) that can be used to control a tungsten filament lightbulb on an AC or DC circuit, in addition to controlling certain other loads. When power is initially applied to a tungsten filament lightbulb, there can be a momentary but substantial increase in current because cold tungsten has a very low electrical resistance. A "T rated" switch is designed to be able to handle this momentary increase of current.
View larger image (T rated switch; 396KB)
On another GE switch that is of the AC/DC general use variety but which is not pictured on this page, there is the rating 15A 120V AC 5A 250V 10A 125V T and there is no "AC only" indication. This rating appears to indicate that the switch has a maximum rating of 15 amps for most purposes when used with 120V AC but that the lower rating of 10 amps applies when controlling a tungsten filament lightbulb, likely because of a cold filament causing a momentary inrush of current and putting additional strain on the switch contacts that would not occur when the switch is used in other circumstances. (Though it is not clear, the 10 amp rating may also apply if the switch is used with DC.)
In the photo below there is a different item of electrical hardware in the form of an electrical fuse. This electrical fuse is rated for 30 amps at 125 volts and has an Edison type screw base of the same type used on light bulbs. (To guard against the situation where a fuse is replaced with a different fuse that has the same screw base but an improper rating, the use of Edison base fuses is disallowed in new installations. "Type S" fuses are an alternative that use differently threaded adapters to prevent mismatched fuse ratings.) The fuse pictured below has a notable feature in the form of a slot on the end of the handle and what appears to be a neon indicator bulb inside.
View larger image (Signalite electrical fuse; 136KB)
The front end of the fuse where the handle is appears to be made of hard plastic and carries the designation "6-SIGNALITE-6"; the other end of the fuse appears to be a porcelain cone with a metal contact. The July 1948 issue of Popular Science describes the Signalite fuse as containing a neon bulb that comes on to indicate when the fuse has blown. In addition, the fuse contains six elements and it is possible to engage a different element when one has blown by turning the fuse handle clockwise. The manufacturer is specified as Signalite Fuse Co. of Bloomfield, New Jersey, USA.
The photo below shows a Pyrotite electrical fuse which is rated for 30 amps at 125 volts. The fuse is made almost completely of metal and porcelain and it carries a reference to a US patent which was issued to the Bryant Electric Company of Bridgeport, Connecticut, USA on April 27, 1909. The patent describes a design where a fuse has a large hollow interior space, a flat metal strip with a narrow section that can "blow," and a somewhat flexible cover (i.e. of mica.) The specified advantage of such a fuse design is the need for neither vent holes nor smothering/padding material inside. For the fuse shown in the photo below, there appears to be a mass of light-brown solid powder or paste inside at the point where the fuse strip reaches the rim of the porcelain cup, near the 5 o'clock position with regard to the front of the fuse. Though the age of the depicted fuse is unclear, the 1909 McGraw Electrical Directory from the General Electric Company mentions "Pyrotite" fuses of porcelain and mica from the Bryant Electric Co.
View larger image (Pyrotite electrical fuse; 396KB)
This web page is copyright © 2012-2017 by Richard Green. The photos of electrical hardware are copyright © 2012 by Richard Green. All rights reserved. Unauthorized reproduction is prohibited. All trademarks are the property of their respective owners. To contact the webmaster, please use the contact form or send e-mail to richard at thedoorintomorning dot com. If you are interested in encrypted e-mail messaging (PGP/GnuPG), please inform the webmaster. This page was last updated on March 14, 2017.
The ad for HYLO light bulbs is from The American Magazine, October 1917 (Vol LXXXIV No. 4), on page 72. This ad is out of copyright in the USA because it was published prior to 1923. The ad for the Con Cord Fireplace Flicker Flame extension cord is from page 89 in the October 1951 issue of Popular Science. The ad for the Dremel Moto-Tool product is from page 234 in the April 1940 issue of the same publication. These ads appear to be out of copyright in the USA because they were published without a copyright notice prior to 1978. Foreign copyrights may apply.