busted fuses of manufacturing equipments

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ACidGaMbiT

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what could be causing fuses to bust for a manufacturing equipment? the downstream side of the fuses are connected to an MOV/ varistor. Also the equipment's main circuit breaker's downstream side is coupled to an EMI filter. could transient or voltage causing these? thanks.
 
ACidGaMbiT said:
what could be causing fuses to bust for a manufacturing equipment? the downstream side of the fuses are connected to an MOV/ varistor. Also the equipment's main circuit breaker's downstream side is coupled to an EMI filter. could transient or voltage causing these? thanks.
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Could you provide a little more info?

Are they actually breaking apart, or just blowing?

What kind of fuses... circuit voltage? ... size?

Are they sized appropriately?
 
the equipment is for a semiconductor company where i am working for. the fuse is rated 1 A as per diagram. 5 A was tried and still it blew up. the source is 480 V. one more thing that I've forgot to mention is that it's MOV got damaged also. a PQ device was installed on its distribution CB to check if there are PQ issues that may caused this problem. the equipment is now running for two hours with no interruption after the fuses and MOV were replaced. what could be the root cause behind these? thanks and sorry for the duplicate post.
 
I'm afraid this question if far too general for us to be much help. Fuses blow when there is too much current flowing through them. There is nothing wrong with your fuses, you just need to figure out where the high current is coming from.
 
I would double check your fuse ratings as far as voltage and AIC ratings. Many times I have seen folks substitute the wrong fuse especially on the smaller amperages. Many will "explode" when they detect a short as would possibly be the case with your MOVs
The protection ahead of these fuses will also be of importance. Do you know the withstand rating on the equipment itself ?
 
Normally semiconductor fuses are very fast blowing. If you do not use a very fast blow fuse on the semiconductor, the semiconductor will go before the fuse will.

Its possible that you are seeing some transients that are causing the MOV to turn on. While it is on, it is basically a short circuit so the fuse could see a lot of current for a very short time. It could well be even to blow the fuse.
 
A small amperage fuse with a MOV located downstream will indeed blow during a surge event that would normally not be an issue for the MOV or the equipment.

The best way to protect both the equipment and thwe MOV would be to do the following:

line in - 15amp slo-blow fuse - EMI filter and MOV - fuse rated to protect the equipment.

Note that the equipment fuse is now "downstream" of the EMI filter and MOV, that means it should only blow for an actual equipment fault.

The 15amp slo-blow fuse should only fail if the EMI filter or MOV takes a surge in excess of their capabilities.
 
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