Is a normal blow fuse the same as fast acting?

Everything you ever wanted to know about fuses.

http://www.flippers.com/fuses.html

One thing John doesn't discuss is what "MDL" stands for.

"AGC" stands for "automotive glass cartridge"
"MDL" stands for "method detection limit"

It is generally understood that an "AGC" fuse is fast blow whereas a "MDL" fuse is slow blow.

In the glass cartridge variety for the 1/4 x 1 1/4" size, "time delay" fuses are

New Edison - MDL
Old Edison - BDL
Bussmann - MDL
Old Bussmann - MSL
Gould - GDL
Littelfuse - 313

For "fast acting"
New Edison - AGC
Old Edison - BGC
Bussmann - AGC
Gould - GGC
Littelfuse - 312

If you look at this old Bussmann catalog that John Robertson posted - http://www.flippers.com/pdfs/Buss_Fuses_Catalog_569.pdf - you will notice that not all fuse values come in all types. It also distinguishes between "fast acting" and a "glass tube" fuse in the 1/4" x 1 1/4" size where the fast acting will open at 200% load in 5 seconds or less. And while I would say this is one of the defining features of a fast acting fuse, most people would say that "fast acting" = normal blow and "time delay" = slow blow.

viperrwk
 
they are the same thing....i just loaded a fast acting 3amp 250v where a 3amp 250v normal blow should be and it had zero problems.
 
they are the same thing....i just loaded a fast acting 3amp 250v where a 3amp 250v normal blow should be and it had zero problems.

false. they are most certainly NOT the same thing. plz don't be ignorant of this.

A slow blow fuse is different from a fast acting fuse in its capability to withstand transient pulse currents, i.e., it can withstand the surge current upon power-on/off, thus ensuring the equipment works normally. Therefore, slow blow fuses are often called time-delay fuses. Technically, a slow blow fuse features a higher I2t value, and it requires more energy to blow, so it is more capable of withstanding pulses compared with a fast acting fuse of same rated current.

When an overcurrent occurs in a circuit, the breaking time of a slow blow fuse takes longer than that of a fast acting fuse because of the larger I2t. Is it less protected this way as some people are worried? The answer is no. Once the circuit fails, the overcurrent will last and corresponding energy released will go beyond the I2t of the fuse until it blows out. The timing difference of slow blowing and fast acting is not significant to their protection. Slow blowing will affect the protection performance only when sensitive components existing in the protected circuit need to be protected.

Due to the previous difference, slow blow and fast acting fuses are applied to different circuits. Fast acting fuses must be used in purely resistive circuits (no or fewer surges) or the circuits where IC and other sensitive components need to be protected, while slow blow fuses are preferably used in capacitive or sensitive circuits where surges occur upon power-on/off and power input/output. Apart from circuits for IC protection, most applications with fast acting fuses can be replaced with slow blow ones to enhance anti-surge capability. Contrarily, replacement of applications with slow blow fuses to fast acting ones may cause the fuse to break as soon as the equipment is switched on and fails to work.

Furthermore, economic consideration is also an indirect factor for selection because a slow blow fuse is much expensive than a fast acting one.
- from: http://aemcomponents.com/applications/faq/
 
there is still a difference between fast acting, normal blow, and slow blow (time delay)

If anyone would actually bother to read the data sheet you would see the differences in I2T ratings and other surge related parameters.

It may not matter in this instance since the only purpose the 3A fuse has is to protect the yoke coil from blowing up when the thing fails, and the yoke can take quite a beating.
 
there is still a difference between fast acting, normal blow, and slow blow (time delay)

If anyone would actually bother to read the data sheet you would see the differences in I2T ratings and other surge related parameters.

It may not matter in this instance since the only purpose the 3A fuse has is to protect the yoke coil from blowing up when the thing fails, and the yoke can take quite a beating.

Can you link to the data sheet and (or if in the doc above) post the page number?
 
Back
Top Bottom