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double throw disco #36275 04/03/04 02:19 AM
Joined: Feb 2004
Posts: 17
S
seattleman Offline OP
Member
Has anyone used a double throw safety switch. Just wondering what applications this had been used for.

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

Re: double throw disco #36277 04/03/04 06:43 AM
Joined: Dec 2000
Posts: 4,286
electure Offline
Member
Manual transfer switch, as Paul says.

Re: double throw disco #36278 04/03/04 08:32 AM
Joined: Mar 2001
Posts: 93
M
Matt M Offline
Member
We use them all over the place in the factory that I work at to reverse 3-phase motors. Matt

Re: double throw disco #36279 04/04/04 09:25 AM
Joined: Jun 2001
Posts: 642
N
nesparky Offline
Member
Another use is to select which load gets power when the same source runs one OR another load.


ed
Re: double throw disco #36280 04/04/04 03:05 PM
Joined: Apr 2002
Posts: 2,527
B
Bjarney Offline
Moderator
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.]

Re: double throw disco #36281 04/04/04 04:51 PM
Joined: Sep 2001
Posts: 806
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NJwirenut Offline
Member
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.

Re: double throw disco #36282 04/04/04 09:37 PM
Joined: Apr 2002
Posts: 2,527
B
Bjarney Offline
Moderator
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.

Re: double throw disco #36283 04/04/04 10:03 PM
Joined: Apr 2002
Posts: 2,527
B
Bjarney Offline
Moderator
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}
[Linked Image from 6l6.net]
Note also the two applications on page 24 fig. 8-7 — “two sources” versus “two loads”.
[Linked Image from 6l6.net]




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

Re: double throw disco #36284 04/05/04 01:18 AM
Joined: Mar 2004
Posts: 11
K
kody wilson Offline
Member
should it be called a three posion insted of a "double trough"?


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