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Topic Title: Rating of fuses / cables
Topic Summary: Rating of fuses / cables
Created On: 26 September 2013 05:19 PM
Status: Read Only
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 26 September 2013 05:19 PM
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nickstick

Posts: 1
Joined: 01 May 2013

When sizing a fuse, there are various derating factors that should be taken into account, ambient temperature, frequency, altitude etc etc.

The cable current rating taken from the IEC standards must be greater than or equal to the nominal current of the fuse. But do you take the derating factors into account when sizing a cable? To put it another way, is In always the value printed on the side of a fuse, or is it In x derating factors.

For a hypothetical example, a 200A fuse is installed in a hot ambient, at altitude carrying high frequency harmonics. So the max rms current for the fuse is derated to 160A.

So is the cable rated at 200A or 160A? My feeling is that the cable should be rated at the 200A, but I need to be able to back up my position.

Thanks
Nick
 26 September 2013 07:34 PM
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Zuiko

Posts: 518
Joined: 14 September 2010

Of course,

If your current carrying capability is derated by 20% because of the environment; you cannot chose a smaller cable, because the smaller cable would be derated, and you would end up compounding the problem!

When you are derating a cable, you end up with a bigger cable not a smaller one!
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