# Open circuit?

1. Oct 22, 2005

### asdf1

The statement, "when a resistor fails, it will normally open." is true.
But I don't understand:
when a resistor fails, doesn't that mean that the resistor doesn't work? so doesn't that mean that resistance=0=short circuit?

2. Oct 22, 2005

### Staff: Mentor

If a resistor burns out so that the counductive material is disrupted, then it is an open circuit with infinite resistance, i.e. conductance = 0.

If somehow, the resistor short circuits then it has no resistance (and it is then no longer a resistor).

Last edited: Oct 22, 2005
3. Oct 22, 2005

### asdf1

is a failed resistor one that has 0 resistance?

4. Oct 22, 2005

### FredGarvin

A resistor is "failed" when it doesn't provide the amount of resistance it is rated to, whether it be too much or too little.

5. Oct 22, 2005

### Ouabache

That's a good point. Perhaps I can expand on that..
Resistors are given a tolerance rating, which could be within 1%, 2%, 5%, or 10% of its nominal value. (You will see what I mean by following the link). If your resistor has a tolerance of 1% and it now measure more than that, it fails to meet its specification. Its a bad part and cannot be trusted to hold even its present measured value in a circuit.

asdf1 said, "when a resistor fails, it will normally open" . A resistor normally heats up as it conducts current. If the resistor is weakened or defective, that heat can cause the resistor to fuse open. Just like a real fuse, the resistor becomes an open circuit.

Last edited: Oct 22, 2005
6. Oct 23, 2005

### asdf1

i see! thanks!!! :)