Safety Switch or Disconnect Switch

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
Both terms are correct and interchangeable.
The term "safety switch" refers to an enclosed switch and goes back some 100+ years when open style, think Dr. Frankenstein, switches were very common. In fact putting enclosures around open style switches is responsible for the name 'Square D'

Of course there will be some local slang usage that comes into play, just like there is for many electrical products.
 

garbo

Senior Member
Have to say fused or non fused safety switch when asking for one at supply houses. One time I asked for a 250 volt three pole non fused safety switch and after I took it up to the roof & opened the box found out it had two poles and a neutral block. Never made that mistake again. Wish they still made the original best in class bullet proof Bulldog safety switches like the ones they made in the 1970's. They got sold at least twice and turned into garbage with plastic parts inside.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
I see no reason to use the term safety switch. Disconnect switch is much more useful.
 

synchro

Senior Member
Location
Chicago, IL
Occupation
EE
Personally, I dislike the use of the term “disco” for this. I lived through the Disco era, I don’t ever want to be reminded of that…

Two of my coworkers were at the Disco Demolition Night at Comiskey Park in Chicago, but they stayed in there seats and were not part of the crowd that rushed the field. At least that's what they told us. ;)

https://en.wikipedia.org/wiki/Disco_Demolition_Night
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Consulting Electrical Engineer - Photovoltaic Systems
Still have your Leisure Suits, huh?? :)
Actually, I do. Once a year I go to a party during Mardi Gras in Lafayette, LA, where leisure suits are the costume of choice for the male participants. The women dress as Krewe Sluts. That's a Frank Zappa reference for those of you too young to remember Uncle Frank
:D

 

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
I see no reason to use the term safety switch. Disconnect switch is much more useful.
A “disconnect switch” can be any number of devices, a safety switch (in this context) is a specific type of disconnect switch.

The Square D story, for those who never heard it, is that the company was originally called McBride Manufacturing Co., but started making fuses, so changed to the "Detroit Fuse Manufacturing Co." based, obviously, in Detroit. But at the time, fused switches were, as mentioned, the open knife switches, like in the Frankenstein movie set, where anyone walking by and brushing up against the conductive parts could be shocked or killed. Ford wanted something less dangerous for their new assembly lines and since they were using Detroit fuses, Ford came to them for ideas. Detroit Fuse enclosed the knife switch (at first in a cast iron box, but by 1915 it became sheet metal) with a handle to the outside to operate it.
Detroit Fuse Co Safety Switch.jpg

The idea was wildly popular. Detroit Fuse put their logo on the front of the box, a "D" for Detroit, in a square box, to represent the enclosed aspect of it. But over time, people just kept referring to them as "them switches with the square and D on 'em". Eventually that became so much more important to their business than the fuses, that they sold off the fuse production and changed the name of the company to The Square D Co. (and later, just Square D).

1921 advertisement;
439px-SquareD_SafetySwitchAd_JonesIsDead_1921.jpg
 
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