single fuse blown

[salem]

Hi'
in three phase motor circuit, is it required to replace all the three phases fuses' if one phase fuse blown ?

 

[DRWeig]

No, no good reason to replace good fuses...

Have you determined why one fuse is blown?

Best to you,

Goober Dave

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[jraef]

I disagree. In a three phase system, unless there is a ground fault, the event that causes one fuse to blow must have occurred in at least two of the phases, but you only see the one. The fuse that cleared was just the first one to go and once it cleared, the current stopped so the other(s) didn't need to clear. But they still saw some if not most of the fault current up to that point and are stressed. That means it might take less current to cause the other fuses to clear next time. That is not inherently dangerous, but it is a nuisance.

If you cut open a good fuse and look at how they are made, you can better appreciate how the near-clear fault current can deform the fuse element and weaken it. Years ago when I started in this industry, we used fuses with replaceable links (now illegal here in the US). My first boss made us replace all 3 links if one blew, and that gave us newbies the opportunity to see the other two "good" fuses. It was an eye opener.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[ScottyUK]

Agree with jraef, replace the set. Whatever cost you save in fuselinks will be eaten up when someone has to come back and replace the already-weakened fuse when it fails; normally failure occurs sometime after you've left site for the night and some poor sod gets called out on a breakdown. Leaving latent defects on the system is a great way to lose friends.

 

[jraef]

Murphy's Law says that the next fuse will fail only after you have reached the maximum distance away from your facility, and only when you are on call...


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[ScottyUK]

In my experience Murphy was an optimist.

 

[waross]

If you are lucky the starting surge will take out the secnd fuse while you are stll at the motor. That will avoid an expensive return call to replace it later.
Moderate overloads may be the worst. By the time one fuse melts through and clears the other two may be partly melted and badly compromised.
Yes! Replace all three fuses.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[itsmoked]

When I was about 13 and repairing a TV scrounged out of a house fire I happened to be looking at the fuse when I powered the TV up. It was easy to see the fuse as the case had melted off the back. When powered up the fuse flashed orange like a dim incandescent filament every time. That fuse would last about 4 months of service then snap in two like clockwork. It was failing on being worked as close inspection would see it start to kink as it got longer when hot.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[DRWeig]

I stand corrected!

Best to you,

Goober Dave

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[LionelHutz]

Well, it's not "required" Dave...

You also asked a good question - if it's known that the fuse blew due to a single phase to ground short then you know the other fuses weren't stressed by the fault.

The nature of the equipment can play a role too. We don't change good fuses in our test bench area.