fuses


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Old 08-31-06, 06:55 PM
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fuses

Is it ok to replace a non-slow blow fuse with a slow blow? Are 20 amp fuse types (slow blow, time delay etc) interchangeable as long as they all say 20 amps? Thank you if anyone can explain this.
 
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Old 08-31-06, 07:15 PM
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a fast acting (non-slow blow) fuse will burn out as soon as the current gets to the rated current. A slow blow fuse will give you a time delay to allow for high inrush things like motors to start. When a motor starts, it pulls many times its nominal operating current. The slow blow allows for this high starting current and will only burn out on at rated current on a much longer duration. To answer your question, it depends on the applicaion. Typically there would not be much harm in the replacement, but there might be certain circumstances that it would cause a problem. What does the fuse protect?
 
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Old 08-31-06, 07:23 PM
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As Scott explained, the slow blow/time delay fuses are used to allow motors to start. While they can be used on any circuit, they do not serve much of a purpose on a circuit that does not have a motor, for example, on it.

A typical application might be where a freezer is on the circuit. The freezer and whatever else is on the same circuit do not require more current than the circuit can supply, except for the brief period of time when the compressor of the freezer kicks on. If this in rush of current blows the fuse, then a time delay fuse is called for.
 
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Old 08-31-06, 11:49 PM
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It is an ordinary circuit in an apartment, with an air conditioner on it. The a/c would sometimes blow the fuse so I replaced it with a slow blow and that fixed it. The only thing that concerns me is that you say it wouldn't do "much" harm.
 
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Old 09-01-06, 05:29 AM
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Some would say that replacing a fuse in an apartment, or more apporopriately changing the fuse, ahoukld not be done by the person renting the apartment. I won't attampt to address that issue.

What I will say, however, is that you had better be darn sure that this is a circuit capable of handling 20 amps. Now that YOU have put in a 20 amp fuse, it will be your problem if 20 amps is the wrong size and the circuit really is only a 15 amp circuit. Yiou could be contributing to a fire.
 
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Old 09-01-06, 05:49 AM
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slo-blo

These days, "slo-blo" protection is essentially a requirement and is provided by CBs. The slow reaction fuse I'm familiar with is the "Fusetron" which had assorted screw bases that were tailored to the fuse rating. For example, a 20a type can not be inserted into a 15a receptacle. I have not seen a fusebox still in use, ordinary or fusetron, in years except in old and non-updated inner city houses.
 
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Old 09-01-06, 09:40 AM
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You are safe with a time-delay plug fuse protecting this circuit, with the caveat that the fuse-rating does not exceed, but equals, the ampacity of the circuit conductors .
 
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Old 09-03-06, 02:38 AM
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Ok, to sum up then, make sure fuse has same rating, if in apt check with landlord, use only when needed due to loads with higher starting current because although still considered safe they provide a bit less protection.
 
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Old 09-03-06, 04:56 AM
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NEVER replace a slow blow with a fast blow and viceversa. Guys fuses are there for one purpose and one purpose only to protect. how can a slow blow protect a circuit that if the current exceed the limit it blows parts. A slow blow does not delay anything period but it allows current to pass in excess before it itself blows. A 20 amps fuse will blow at specified a slow blow will do the same thing at 20 amps but it will require a more sustained overcurrent condition for a longer time. And finaly a fuse the size of a beer bottle for 300 amps does not means that the core is huge in wire size. TAKE IT APART you will find a strip of jagged strip of 2-3 mills the rest is SAND. If someone is interested of why i will explain later.
 
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Old 09-03-06, 07:55 AM
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Sorry neon. You advice is not accurate. It is factually true but does NOT apply here. Either fuse is fine.
What if the fuses were replaced with breakers? As Volts says, breakers are inherently time delay.

Gortek, listen to the others. They are spot on.
 
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Old 09-06-06, 04:01 PM
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Talking

As everyone stated, the reason to use a "slow-blow" fuse is for motor loads. If you read what Gortek posted, he said that he was replacing the fuse on an a circuit with an AC. That's exactly what these fuses are made for.

Don't worry, you still have the same protection rating as the "one time" fuse that you replaced. Your apartment will not burn down.
 
 

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