Fuses time delay or not.

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Old 11-17-14, 03:45 PM
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Fuses time delay or not.

The other day a customer wanted a replacement for the round glass fuses. An exact replacement of this type. This was for a typical house hold and if memory serves me correctly it was 20 amp. I looked at her old fuse and saw that it said time delay, so that's what I sold her.

My question, is a time delay fuse typical for a normal household use? I thought an instant blow would be more common. And why would a time delay be used in a household environment?

 
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Old 11-17-14, 03:54 PM
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No, just like breakers they are slow blow. That's so motors that may draw 3 times the running amps or more can start with out blowing the fuse.
 
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Old 11-17-14, 04:08 PM
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Think of the effort you have to put in to taking off on a bike. You push and push and eventually you get some momentum and it becomes easier to peddle.
A motor has to do essentially the same thing to get something spinning when it is in a still position, so it draws a huge amount of current at startup, then drops to the running current stamped on the nameplate.
As ray said, if you did not have a time delay fuse, you would instantly blow the fuse as soon as you turned on the vacuum for example.
Look up "inrush current" if you're curious and would like to learn more.
 
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Old 11-17-14, 04:28 PM
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Yes of course. I should've thought of that myself.
 
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Old 11-17-14, 05:33 PM
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Don't feel bad. I have seen professional electricians not know. Grew up in a small town. While still working and living there I bought a 18,000 BTU window A/C. The house's 60 amp breaker box had no open spaces so I called the local electrical contractor to get a 240 receptacle installed. Well instead of adding a breaker subpanel they installed a fused disconnect next to the meter. They didn't even bother to test before leaving. When I got home that night the A/C ran all of 30 seconds before blowing the fast blow fuses they put in. Just how stupid could you be. Had to the sweat the night out till I could buy some time delay fuses the next day.
 
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Old 11-17-14, 06:33 PM
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ray,
Having a brain fart and not putting in the right fuses... ok, sometimes stuff happens.
But not testing is a pet peeve of mine. The last jman I worked with didn't like to "waste time testing" and I found it embarrassing when we would get callbacks every so often because he did something wrong and didn't test.
 
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Old 11-17-14, 06:37 PM
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Well Mr. A how about the fused disconnect next to the meter. Just imagine how that was probably connected.
 
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Old 11-18-14, 05:10 AM
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Not sure if it is local, but we can't just replace Edison based fuses on a remodel. We have to provide inserts and Fusestats, which all have different sized bases considering the amperage of each. One failing I remember was grand dad increasing the amperage rating of fuses in his fusebox, way back last century, until he smelled wires burning. Totally possible with Edison based fuses, but not possible with Fusestats.
 
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Old 11-18-14, 02:59 PM
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It is possible with fusestats but only if you put in the wrong insert
 
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Old 11-18-14, 04:26 PM
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Thats funny Larry,
Just today I installed a new panel in a farm garage and saw these for the first time in person.
14AWG wire everywhere with 15-30A fuses. Guy had a 50A welding receptacle wired with #8 but 30A fuses, air compressor, and several trucks plugged in to a single circuit. Also had a fused disconnect rated for 60A but 50A fuses in it.
Guy: "Yeah I keep replacing fuses like crazy and don't know why so I called for a new panel"
 
 

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