fuses in series

[Willbe]

Why would anyone put a 500v 2A fuse in series with a 250v 1A fuse in series with the common lead of a Simpson 260?

 

[flat5]

Why? and why the common lead?
You will not be protected to 750 volts.
The max current will still be 1 amp.

What might make some sense is a 2 amp fast in series with a 1 amp slow. Not sure if that will have the desired result it implies.
I don't know how fast a 1 amp slow fuse opens when you feed it 2 amps.

 

[power58]

No real reason to do such a thing. The 260 Voltage measuring circuit would never load enough to blow a 1 amp fuse. If you were measuring current the 1 amp would blow first. Seems an odd set up.

 

[dark]

Why would anyone put a 500v 2A fuse in series with a 250v 1A fuse in series with the common lead of a Simpson 260?

When Fuse is put in series , they are derated very heavily , if I recall there are graphs which has to be analized to understant the I2T for your combination.

 

[Willbe]

What might make some sense is a 2 amp fast in series with a 1 amp slow.

You may have it. A 500v fuse will probably open faster than a 250v fuse. I should go back and look in the P/L and then go to the trip curves.

 

[ericgibbs]

Why would anyone put a 500v 2A fuse in series with a 250v 1A fuse in series with the common lead of a Simpson 260?

hi,
This is what the 260 manual states:

 

[Willbe]

hi,
This is what the 260 manual states:

Thanks, Mr. G.

I've e-mailed Bussman and Littlefuse for trip curves on these buggers. I see now that I also should have asked for interrupting capacity.

I also cut & pasted your link for further reference.

Today I have learned something.

 

[ericgibbs]

Thanks, Mr. G.
I've e-mailed Bussman and Littlefuse for trip curves on these buggers.

hi Mr W.

Attached is the manual, in case you dont have it already.

 

[Diver300]

The early Fluke multimeters also had two fuses.

The idea is that a cheap fuse will blow if the current is a bit larger than it should be, where the current is 10 amps or so, or where the voltage is small. This is quite common so it is convenient to have a cheap fuse.

If the meter is used incorrectly, and left on amps and connected to a high voltage supply that can supply thousands of amps, the is a big risk that the cheap fuse will not stop the current. The short circuit current can exceed the Breaking capacity - Wikipedia, the free encyclopedia of the fuse. The current continues to flow across an arc where the fuse used to be.

This is when the expensive fuse blows and saves the user's life / sight / eyebrows.

 

[Willbe]

The plot thickens. . .

The Interrupt Rating for the 312001 (1A) is 10kA @ 125Vac, 35A @250Vac., and for the BLS002 (2A) it's 10kA @ 600Vac

Apparently Simpson was concerned interrupting current from voltages over 250v. Higher V is more prone to arcs.