Fuse protection of 84 137 020, fuse selection Outline · [ Standard ] · Linear+

[anitalyq]

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!

[Ronnie Haiduk]

Hi, to select the proper fuse for solid state relays the I²T of the fuse must be less than the I²T 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 I²T 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/.

[anitalyq]

Could you please recommend the exact type of ferraz shawmut for this case?
Thanks a lot!

[Ronnie Haiduk]

Do you want a fuse to protect the relay or to protect the load?