What happens when a resistor is in parallel with a short circuit?
Nothing happens to a resistor in parallel to a short circuit. It still is a resistor and still has its rated resistance. If you try to pass current through it the short keeps the IR drop equal to 0V. Thus no power will ever be dissipated in the resistor.
Do resistors fail short or open?
Resistor failures are considered to be electrical opens, shorts or a radical variation from the resistor specifications. A fixed composition resistor normally fails in an open configuration when overheated or overly stressed due to shock or vibration. Excessive humidity may cause an increase in resistance.
What happens when a resistor fails to short circuit?
Generally speaking resistors fail short circuit, but a high value resistor, with a voltage across it exceeding its maximum voltage rating, can fail short by arcing over, which can drastically reduce the resistance value. I think Hero999 means generally open circuit.
Why can a 20 ohm resistor be ignored?
When there is two resistor in parallel then the current divides itself accordance to conductance of the resistors. The more conductance the more current. Here we have a resistor with unlimited conductance, so all current flows through it. Therefore, the other resistor has no effective value. That’s why the 20 Ohm resistor can be ignored.
How can you tell if a resistor is bad?
Because of this, the result of a failed resistor can be difficult to debug. Direct measurement outside of the circuit is usually the best method for checking any device, but in most case this means physically removing the device, and doing so may cause the failure to disappear (hairline solder shorts, internal defects, etc.).
Why do resistors always open under fault currents?
In high-energy circuits, it’s important to either use a fuse in line, or specify a fusible resistor, which is tested to always become open under fault currents. About permanent changes in resistance: these are more likely in older-style carbon composition resistors.