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> Fuse protection of 84 137 020, fuse selection
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anitalyq
post Apr 6 2006, 04:33 AM
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We have installed hundreds of the captioned SSR for controlling mains power to the air-conditioner. In order to protect the SSR from damage, we would like to install a fuse at the output side. We would be grateful if you can advise us the detail specifications ( normal rating, breaking capacity and type ) of the fuse for such application.
Can the 13A mains fuse ( high breaking capacity of 6000A @ 250VAC, fast blow type ) be used for this application.
Please be informed that we cannot find I2t value for the mains 13A fuse ( RS stock number is 412-605, www.rshongkong.com ), but the I2t is surely different from the breaking capacity ( the units of them are different and specifications of RS# 420-145 also have different values: breaking capacity of 1500A and I2t of 26 ).

Please advise the relation between I2t and the max. non-rep. 1- cycle surge. To my understanding,

if t = 20 ms ( 1 cycle of 50 Hz ), then I2t = IxIx 0.02 = 3042 ( for 50 Hz ), then I = 390, then 1 cycle surge shall be 390 A instead of 780 A ( exactly double of the calculated value );
if t = 16.67 ms ( 1 cycle of 60 Hz ) , then I2t = IxIx 0.01667 = 2535 ( for 60 Hz ), then I = 390, then 1 cycle surge shall be 390 A instead of 780 A ( exactly double of the calculated value ).

If we cannot find the I2t value of the fuse, and not practical to change the 50A SSR to 75A SSR ( hundreds of 50A SSR are being used ), can you recommend fuse ( breaking capacity, rating and type ) for protection of the SSR.

Thank you very much!
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Ronnie Haiduk
post Apr 6 2006, 08:06 AM
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Hi, to select the proper fuse for solid state relays the IT of the fuse must be less than the IT of the relay. In this case it has to be less than 2458. Typically you will have to use a semiconductor fuse. You want to use the melting IT rating of the fuse. I would recommend using Ferraz Shawmut fuses. They have a variety of different body styles to choose from. To get the proper fuse I would reccomend you visit their web site, http://www.ferrazshawmut.com/.


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anitalyq
post Apr 6 2006, 10:21 PM
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Could you please recommend the exact type of ferraz shawmut for this case? unsure.gif
Thanks a lot!
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Ronnie Haiduk
post Apr 10 2006, 07:01 AM
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Do you want a fuse to protect the relay or to protect the load?


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