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#36275 - 04/03/04 03:19 AM double throw disco  
seattleman  Offline
Joined: Feb 2004
Posts: 17
Seattle, WA, USA
Has anyone used a double throw safety switch. Just wondering what applications this had been used for.


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#36276 - 04/03/04 05:03 AM Re: double throw disco  
pauluk  Offline
Joined: Aug 2001
Posts: 7,520
Norfolk, England
I would have thought one of the most common uses would be to select different power sources, e.g. utility power or generator.

#36277 - 04/03/04 07:43 AM Re: double throw disco  
electure  Offline

Joined: Dec 2000
Posts: 4,259
Fullerton, CA USA
Manual transfer switch, as Paul says.

#36278 - 04/03/04 09:32 AM Re: double throw disco  
Matt M  Offline
Joined: Mar 2001
Posts: 93
Laporte, MN, USA
We use them all over the place in the factory that I work at to reverse 3-phase motors. Matt

#36279 - 04/04/04 10:25 AM Re: double throw disco  
nesparky  Offline
Joined: Jun 2001
Posts: 642
Another use is to select which load gets power when the same source runs one OR another load.


#36280 - 04/04/04 04:05 PM Re: double throw disco  
Bjarney  Offline
Joined: Apr 2002
Posts: 2,527
West-Southern Inner-Northeast ...
Note that nowadays there are two styles of ‘double-throw’ XOP switches. See
A newer style has two sets of movable blades and two sets of fixed jaws. Older is one set of movable blades and two sets of fixed jaws. (Note upper vs. lower photos.)

[I believe Cutler-Hammer has a similar variation.]

#36281 - 04/04/04 05:51 PM Re: double throw disco  
NJwirenut  Offline
Joined: Sep 2001
Posts: 806
Bergen County, NJ
AFAIK, the 2 different variations in construction are a result of fusible or non-fusible design.

The extra length needed for 2 sets of fuses requires 2 separate interlocked switch mechanisms, while a non-fused switch can be made with a single set of blades.

#36282 - 04/04/04 10:37 PM Re: double throw disco  
Bjarney  Offline
Joined: Apr 2002
Posts: 2,527
West-Southern Inner-Northeast ...
NJ, that is a good point. I installed one fusible double-throw switch in a service-entrance application in the 1970s to accommodate a standby genset. One set of fuses was normally hot through the utility feed [with the switch open.] At the time there was an NEC exception that clearly allowed the practice.

By job completion, a prominent label warned of the condition, and a piece of clear acrylic secured with non-metallic machine screws covered the {utility-powered} set of fuses.

#36283 - 04/04/04 11:03 PM Re: double throw disco  
Bjarney  Offline
Joined: Apr 2002
Posts: 2,527
West-Southern Inner-Northeast ...
Two C-H double-throw switch versions [one set of movable blades versus two] are illustrated on page 26 of {Aaak! 5MB file}
[Linked Image]
Note also the two applications on page 24 fig. 8-7 — “two sources” versus “two loads”.
[Linked Image]

[This message has been edited by Bjarney (edited 04-05-2004).]

#36284 - 04/05/04 02:18 AM Re: double throw disco  
kody wilson  Offline
Joined: Mar 2004
Posts: 11
vancouver wa. 98664
should it be called a three posion insted of a "double trough"?

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