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


#36276 04/03/04 04:03 AM
Joined: Aug 2001
Posts: 7,520
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 06:43 AM
Joined: Dec 2000
Posts: 4,291
Manual transfer switch, as Paul says.

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

#36279 04/04/04 09:25 AM
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 03:05 PM
Joined: Apr 2002
Posts: 2,527
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 04:51 PM
Joined: Sep 2001
Posts: 806
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 09:37 PM
Joined: Apr 2002
Posts: 2,527
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 10:03 PM
Joined: Apr 2002
Posts: 2,527
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 from]
Note also the two applications on page 24 fig. 8-7 — “two sources” versus “two loads”.
[Linked Image from]

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

#36284 04/05/04 01:18 AM
Joined: Mar 2004
Posts: 11
should it be called a three posion insted of a "double trough"?

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