Contact Intermountain Fuse Supply Inc.
Salt Lake City, Utah
Call: 1-800-246-8336
Fax: 1-801-466-1998

 

 

Salt Lake City, UT, US

Now
Partly Cloudy
81°F, Windchill: 81°F
Wind: 12 mph N
Humidity: 15%
Visibility: 0 mi
pressure: 29.78 in falling
Sunrise: 6:58 am
Sunset: 7:53 pm
Sun
Clear/Wind
Hi: 81°F, Low: 44°F
Mon
Sunny
Hi: 70°F, Low: 51°F
How fast?
Monday, 23 February 2009 20:29
How Fast?  The fourth rating for fuses is how fast they will blow. There are very fast, fast and slow blowing fuses. Very fast fuses will blow in as little as 1/200th of a second. They are designed to protect sensitive electronic circuits such as rectifiers and solid state electronics. Fast blowing fuses are designed for non-inductive loads, such as heating elements and lighting. Slow blowing fuses are designed for inductive loads, such as motors and transformers. They will blow fast as well, but only under a short circuit condition. This is because a motor typically draws 3-5 times its rated current during the first few seconds of operation. For example, a 3-phase 2 horsepower, 230-volt motor may be rated at 6.8 amps, but during its first 3 seconds of operation it may draw up to 25 amps. Such a motor would typically be fused with a slow blow, sometimes called "time-delay" fuse, rated at 10 amps. These fuses are normally designed with two seperate elements, one for short circuit protection, the other for overload protection and are referred to as "dual element fuses". The overload link will only get hot enough to blow if it sees an inrushing current sustained for more than the normal start up time of a few seconds. If however, it sees a current significantly higher than the expected inrush current, for example 70 amps, it will blow immediately. So the fuse gives dual protection. It protects from a direct short instantaneously and it also protects a motor which is slowly overheating due to an abnormally heavy load or operation at less than the appropriate voltage.