Doug Fleenor Design DMX Relay Packs use dry contact air-gap relays. These relays have advantages and disadvantages over the solid state relays found in dimmer packs. Solid state relays can be switched on and off rapidly with no wear, but tend to leak current even when in the off position. Air-gap relays do not leak current, but due to their mechanical design have a finite life span. Doug Fleenor Design relay packs should be used where a true-off condition is required (no voltage, no current). They should not be used in applications where they will be turned on and off rapidly (for example in chase lights). DMX512 control of low voltage switch closure devices (such as slide projectors and fog machines) is made possible with these low voltage DMX Relay Packs.