Wirewound resistors are common seen in power supplies and other equipment where lots of power is dissipated. A high-resistance wire is wound on an insulating form — usually a ceramic tube — and attached to electrodes at each end.
  These are made to dissipate a lot of power in sizes from one-watt to hundreds of watts. Wirewound resistors are usually intended to be air cooled, but some styles have a metal case that can be attached to a heatsink or metal chassis to get rid of undesired heat. Microhm Nual Series are metal clad wirewound resistor, chassis installation type, up to 100W.
 
 
Because the resistive material in these resistors is wound on a form, they have very high LS. For this reason, wirewound resistors are not used in audio and RF circuits.

 
Small wirewound resistors look an awful lot like film or carbon comp resistors. There is usually a wide color band on wirewound resistors, but not always. If you’re in doubt, test the resistor at the frequencies you expect to encounter. There are special versions with windings that cancel most of the inductance, but have a much higher CP that also affects the resistor’s performance above 50 kHz.