Does it matter what Voltage resistors work at?

Question

When a resistor (100k) says it works at 500v does this mean that it will work until the amount of voltage passed through it exceeds 500v? after which it will melt, blow up or whatever?

also does it matter what power rating it has? 1W or 2W? will this make any difference?

Thanks in advance

Tom

Answer 1

No it doesn`t matter what voltage a resistor operates at as long as the current through the resistor does not exceed the amount that would cause more power absorption than the resistor is rated at.  For example a 100k ohm resistor with 1000 vdc at one end of it and 900vdc at the other end of it would dissipate the same wattage as a 100k ohm resistor with 100dc at one end of it and 0vdc at the other end of it.

A 100k ohm resistor offers the same amount of resistance to 500 volts as it does to 50 volts or 5 volts or any other value of voltage. Resistors are specified by their ohmic value, wattage rating and ohmic value tolerance. Resistors do not normally have voltage specifications, however  the wattage rating does determines the maximum voltage that can safely be applied across a resistor.

Voltage does not pass through a resistor. Voltage is stationary in location but may vary in amplitude at any location in a circuit. Excessive current flow is what burns up resistors.

Yes it does matter what power rating a resistor has. Since amps squared  times resistance equals watts this means that a 2 watt resistor of a given ohmic value can safely handle 1.414 times as much current as a 1 watt resistor of the same ohmic value.

Answer 2

Voltage does not pass through.

It is current that passes through.

I = 500 / 100 mA

I = 5 mA is the current rating.

If W and V are known, operating current may be calculated.

Answer 3

Voltage is not "passed through" a component. It is measured or applied to.

Yes, the resistor will be damaged if you exceed either it's voltage or it's power rating.

So yes, the power rating of a resistor is important. It is a value not to be exceeded if you don't want to damage the resistor. But if your application is only dissipating 1/2 watt, you can use either a 1 W or a 2 W resistor.

Answer 4

I once needed a load resistor for 1,000 volts.  I only wanted to draw 100 microamps.

R = E / I = 1,000 / .0001 = 10,000,000 ohms

P= I * E = .0001 * 1,000 = 0.1 W

So I need a one tenth watt, 10 meg ohm resitor.  WRONG!!

The resistor failed within hours.  I had exceeded the voltage rating of the resistor.  I ended up with a series string of 1W resistors.  It was gross overkill for the watage rating but it gave me the voltage rating I needed.

As long as you meet or exceed the power rating everything will be OK on power.  But you must also meet or exceed voltage rating...

2W resistors usually have a higher voltage rating than a 1W resistor.

Answer 5

If you exceed the working voltage or power rating of the resistor it is likely to fail.  At worst it will catch light.