{"id":80,"date":"2020-01-13T13:36:19","date_gmt":"2020-01-13T18:36:19","guid":{"rendered":"https:\/\/opentextbc.ca\/basicmotorcontrol\/chapter\/forward-reverse-starters\/"},"modified":"2023-03-02T11:54:50","modified_gmt":"2023-03-02T16:54:50","slug":"forward-reverse-starters","status":"publish","type":"chapter","link":"https:\/\/opentextbc.ca\/basicmotorcontrol\/chapter\/forward-reverse-starters\/","title":{"raw":"Forward\/Reverse Starters","rendered":"Forward\/Reverse Starters"},"content":{"raw":"[caption id=\"attachment_79\" align=\"aligncenter\" width=\"362\"]\"\" NEMA Forward Reverse motor starter with OLR[\/caption]\r\n\r\nA forward\/reverse magnetic [pb_glossary id=\"227\"]motor starter[\/pb_glossary] is constructed from two regular contactors installed with a [pb_glossary id=\"260\"]mechanical interlock[\/pb_glossary] that prevents both coils from pulling in simultaneously.\r\n\r\n[caption id=\"attachment_78\" align=\"aligncenter\" width=\"394\"]\"\" Forward\/Reverse power circuit[\/caption]\r\n\r\nThey are connected so that under normal conditions, one coil will connect L1 with T1, L2 with T2, and L3 with T3. When the alternate coil is energized, Lines 1 and 3 are interchanged with Terminals 1 and 3, allowing for a phase shift in the 3-phase circuit, driving the motor and causing it to rotate in the opposite direction.\r\n\r\n[caption id=\"attachment_79\" align=\"aligncenter\" width=\"394\"]\"\" Reversal of three-phase motor rotation[\/caption]\r\n\r\nBoth coils power contacts feed through a single set of OLR to provide running protection in both directions.\r\n\r\nTo prevent unintentional energization of both the forward and reverse coil at the same time, the coils are equipped with [pb_glossary id=\"230\"]normally closed contacts[\/pb_glossary], which are then wired in [pb_glossary id=\"269\"]series[\/pb_glossary] with the opposite direction's coil to act as an [pb_glossary id=\"259\"]electrical interlock[\/pb_glossary]. This means that if the coil that drives the motor in the forward direction is energized, a normally closed set of contacts wired in series with the reverse coils will prevent that coil from being energized as long as the forward coil remains energized.\r\n\r\nhttps:\/\/media.bccampus.ca\/id\/0_jonttm4k?width=608&height=402&playerId=23449753","rendered":"
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NEMA Forward Reverse motor starter with OLR<\/figcaption><\/figure>\n

A forward\/reverse magnetic motor starter<\/a> is constructed from two regular contactors installed with a mechanical interlock<\/a> that prevents both coils from pulling in simultaneously.<\/p>\n

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Forward\/Reverse power circuit<\/figcaption><\/figure>\n

They are connected so that under normal conditions, one coil will connect L1 with T1, L2 with T2, and L3 with T3. When the alternate coil is energized, Lines 1 and 3 are interchanged with Terminals 1 and 3, allowing for a phase shift in the 3-phase circuit, driving the motor and causing it to rotate in the opposite direction.<\/p>\n

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Reversal of three-phase motor rotation<\/figcaption><\/figure>\n

Both coils power contacts feed through a single set of OLR to provide running protection in both directions.<\/p>\n

To prevent unintentional energization of both the forward and reverse coil at the same time, the coils are equipped with normally closed contacts<\/a>, which are then wired in series<\/a> with the opposite direction’s coil to act as an electrical interlock<\/a>. This means that if the coil that drives the motor in the forward direction is energized, a normally closed set of contacts wired in series with the reverse coils will prevent that coil from being energized as long as the forward coil remains energized.<\/p>\n