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"On Topic" Operations Management Jogging Knife Switches
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<blockquote data-quote="hiro" data-source="post: 2566900" data-attributes="member: 5768"><p>Management isn't supposed to use the disconnects as a means of starting/stopping/jogging a belt, but the reason is mainly the protection of equipment and not for safety reasons. </p><p></p><p>For the most part, it shouldn't be possible to jog one section of a belt by using a disconnect. UPS design calls for each belt to be interlocked to the belt that it feeds. This is done with current sensors (pre '88ish) or SSIs. Obviously, a lot of this depends on the age of the building and what the design called for at the time and if any changes were made over the years. And there are also a few exceptions to the interlock requirement.</p><p></p><p>Again, this is done to protect packages and equipment. If a belt is shut off and the belt feeding it is still running, packages are likely backing up/jamming with the potential for damages and packages setting on a transition point between two belts provides an opportunity for a bag or package to be sucked in and cause more damages or ripping a belt.</p><p></p><p>The video posted can happen, although it is unlikely and the disconnects should have an arc flash shield inside to prevent that from happening. The physical "knife blades" aren't typically designed for constant switching and will prematurely wear out if this is done regularly. Also, there are combo motor starter/disconnects that have a motor starter in the disconnect, although I don't think they are used often at UPS, at least in larger facilities.</p></blockquote><p></p>
[QUOTE="hiro, post: 2566900, member: 5768"] Management isn't supposed to use the disconnects as a means of starting/stopping/jogging a belt, but the reason is mainly the protection of equipment and not for safety reasons. For the most part, it shouldn't be possible to jog one section of a belt by using a disconnect. UPS design calls for each belt to be interlocked to the belt that it feeds. This is done with current sensors (pre '88ish) or SSIs. Obviously, a lot of this depends on the age of the building and what the design called for at the time and if any changes were made over the years. And there are also a few exceptions to the interlock requirement. Again, this is done to protect packages and equipment. If a belt is shut off and the belt feeding it is still running, packages are likely backing up/jamming with the potential for damages and packages setting on a transition point between two belts provides an opportunity for a bag or package to be sucked in and cause more damages or ripping a belt. The video posted can happen, although it is unlikely and the disconnects should have an arc flash shield inside to prevent that from happening. The physical "knife blades" aren't typically designed for constant switching and will prematurely wear out if this is done regularly. Also, there are combo motor starter/disconnects that have a motor starter in the disconnect, although I don't think they are used often at UPS, at least in larger facilities. [/QUOTE]
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