Fusing: Interrupting 100A @ 1VAC vs. 600VAC

[david90]

If a fuse is rated @ 100Amp @ 600VAC, will it able to interrupt a fault @ 100Amp @ 1VAC (hypothetical value)? From my understanding, the 600VAC rating on a fuse is the maximum voltage that a fuse can burn out correclty under a fault condition. If the voltage is too low, won't that cause the fuse element not to burn up since heat = V * I?

 

[berkeman]

If a fuse is rated @ 100Amp @ 600VAC, will it able to interrupt a fault @ 100Amp @ 1VAC (hypothetical value)? From my understanding, the 600VAC rating on a fuse is the maximum voltage that a fuse can burn out correclty under a fault condition.

Correct. The voltage rating of the fuse is dependent only on its geometry, and is an indicator of what voltage can be applied across the fuse after it opens, and you still won't get an arc-over:

http://en.wikipedia.org/wiki/Electrical_fuse

.

 

[sophiecentaur]

If a fuse is rated @ 100Amp @ 600VAC, will it able to interrupt a fault @ 100Amp @ 1VAC (hypothetical value)? From my understanding, the 600VAC rating on a fuse is the maximum voltage that a fuse can burn out correclty under a fault condition. If the voltage is too low, won't that cause the fuse element not to burn up since heat = V * I?

You are right that "Heat is VI" but the V, in the case of a fuse, is the voltage drop across the fuse and not the supply volts.

 

[david90]

I guess my question is not clear :).

My question is why does a fuse with rating 100A @ 600VAC still blow @ 100A with a line voltage of 240V (or does it?) ?

The heat that develops across the fuse element with 100A @ 600VAC should be greater than 100A @ 240VAC. If so, then the fuse in the latter scenario should not blow since the fuse element feels less heat.

 

[david90]

ops nevermind. Brain fart. The fuse element has a fixed resistance value so 100A across it will develop the same voltage drop regardless of line voltage.

 

[Jiggy-Ninja]

The voltage rating is the amount the fuse can handle when open.

When the fuse is good, it's resistance is very low, so the voltage dropped should be very low.

When it's blown, it's resistance is infinite, and it is blocking the current. It has to withstand all of the supply voltage. If the voltage is too high, you might get arcing across it, and it might even weld itself closed. That is obviously a very bad thing.

 

[sophiecentaur]

ops nevermind. Brain fart. The fuse element has a fixed resistance value so 100A across it will develop the same voltage drop regardless of line voltage.

Yes.
Although, of course, when you propose a 1V circuit, you would need a slightly lower load resistance for 100A to flow if a fuse were inserted in the circuit because the fuse resistance is finite. Actually, tin has a resistivity at least 10 times that of copper and a fuse tends to be quite thin so the fuse resistance could be higher than the connecting cable. Certainly, a 1V circuit would have to use pretty thick cables! 230V is a much cheaper system to implement.