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Please refer to the image below:

enter image description here

Taken from the datasheet: http://www.songchuan.com/db/pictures/AdminModules/PDT/PDT090410001/201191913495127935.pdf

lukecam95
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    There is an asymmetry between the operating force and speed (provided by the solenoid) and the release force and speed (provided by a spring). A solenoid is strongest when the airgap is 0 so if it's strong enough to overcome the spring and start pulling in, it's MUCH stronger than the spring when it's closed. That gives a higher current rating when closed by the solenoid, i.e. for a NO contact. –  Aug 23 '17 at 12:17

1 Answers1

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The normally close contact is held by the spring pressure. The normally open contact is closed by the coil, which is stronger (and does not wear out with time as a simple spring). Contact pressure in turn varies the contact resistance (hence the different ratings). See here for more information:

http://www.willow.co.uk/html/components/com_virtuemart/shop_image/product/Catalogues/pdfs/W_Durakool-Contact-Versus-Pressure-Information.pdf

next-hack
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