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#36275 - 04/02/04 11:19 PM double throw disco
seattleman Offline
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Registered: 02/01/04
Posts: 17
Loc: 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 01:03 AM Re: double throw disco
pauluk Offline
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Registered: 08/11/01
Posts: 7520
Loc: 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.
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#36277 - 04/03/04 03:43 AM Re: double throw disco
electure Offline


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Registered: 12/24/00
Posts: 4259
Loc: Fullerton, CA USA
Manual transfer switch, as Paul says.
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#36278 - 04/03/04 05:32 AM Re: double throw disco
Matt M Offline
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Registered: 03/25/01
Posts: 93
Loc: Laporte, MN, USA
We use them all over the place in the factory that I work at to reverse 3-phase motors. Matt
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#36279 - 04/04/04 07:25 AM Re: double throw disco
nesparky Offline
Member
Registered: 06/21/01
Posts: 642
Loc: omaha,ne
Another use is to select which load gets power when the same source runs one OR another load.
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#36280 - 04/04/04 01:05 PM Re: double throw disco
Bjarney Offline
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Registered: 04/10/02
Posts: 2527
Loc: West-Southern Inner-Northeast ...
Note that nowadays there are two styles of ‘double-throw’ XOP switches. See http://ecatalog.squared.com/catalog/173/html/sections/03/17303014.html
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.]
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#36281 - 04/04/04 02:51 PM Re: double throw disco
NJwirenut Offline
Member
Registered: 09/15/01
Posts: 806
Loc: 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.
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#36282 - 04/04/04 07:37 PM Re: double throw disco
Bjarney Offline
Moderator
Registered: 04/10/02
Posts: 2527
Loc: 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.
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#36283 - 04/04/04 08:03 PM Re: double throw disco
Bjarney Offline
Moderator
Registered: 04/10/02
Posts: 2527
Loc: West-Southern Inner-Northeast ...
Two C-H double-throw switch versions [one set of movable blades versus two] are illustrated on page 26 of www.eatonelectrical.com/unsecure/cms1/TB00800001E.PDF {Aaak! 5MB file}

Note also the two applications on page 24 fig. 8-7 — “two sources” versus “two loads”.





[This message has been edited by Bjarney (edited 04-05-2004).]
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#36284 - 04/04/04 11:18 PM Re: double throw disco
kody wilson Offline
Member
Registered: 03/17/04
Posts: 11
Loc: vancouver wa. 98664
should it be called a three posion insted of a "double trough"?
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