# Resistor with allowed voltage 800V but only 25W power rating. How is this possible?

1. Jun 1, 2012

### IronHamster

I recently bought this resistor:

I want to hook it up to about 50V DC, but I want to know if this would be harmful to the resistor. According to the description it can handle up to 800V, but its power rating is only 25W. This doesn't make sense to me, because according to that power rating even a 9V battery would break it.

Anyone know how to reconcile the two? Would 50V be okay?

2. Jun 1, 2012

### AlephZero

Re: Resistor with allowed voltage 800V but only 25W power rating. How is this possib

These resistors come in a wide range of values. The "800V" rating would only make practical sense for the high values resistors and for short duration voltage pulses, so the average power stayed within the 25W power rating.

Alternatively the 800V might be the breakdown voltage between the actual resistor and the outside of the casing. (In other words it would be OK if one end of the resistor was at 800V above ground potential and the other end was 799V above ground).

http://www.nteinc.com/resistor_web/pdf/twentyfive.pdf

At 50V DC the power dissipation would be 50^2 / 0.47 = 5.3 kW, so a 25W resistor isn't going to last very long. It mgiht explode rather than just catching fire, operated so far outside its power rating.

3. Jun 1, 2012

### IronHamster

Re: Resistor with allowed voltage 800V but only 25W power rating. How is this possib

Ah, I understand perfectly. Thanks Aleph!