Content on this page supplied from the web site of Jim Lux

Reasons not to use wirewound resistors beyond their ratings

At first glance, the readily available wirewound power resistor appears to be a good solution to inexpensive high voltage resistor requirements. The breakdown voltage is typically several kilovolts per inch of length, so a 100 watt resistor 6 inches long will probably work at 20 kV, particularly for an application where the substantial inductance isn't a problem. However, in systems where there is a lot of stored energy, the failure mode for these resistors can cause catastrophic damage to other components.

A wirewound resistor is made by winding a very fine resistance element (e.g. Nichrome) on a ceramic form. If a small open develops (the typical failure mode, either due to a physical impact deforming or severing the wire, or due to excessive power disspation) an arc will form at the gap, melting the wire back, making the arc bigger. This is a continuing process that can be quite spectacular.


 Copyright 1997, Jim Lux/ resww.htm / Back to Resistor page / Back to High Voltage Main Page / Back to home page / Mail to Jim (

Main Links Directory

Subscribe to energy2000
Powered by

Encyclopedia of free energy now on CD click for more information