thought i would share this, we have 2 older motion control cars with ac drives and external braking control units. the building was doing a emergency generator test early one morning. everything was fine for the first 15 minutes or so, then the fire alarm system indicated a fire in the machine room. the engineers were on there way up when the emergency generator failed completely. Turns out that both braking units turned on, even with the cars parked at the fire floor, the units remained on until the braking resistors eventually melted and caught the top of the controllers and wiring on fire. the damage was significant as you can imagine. has anyone heard of such a thing? the only conclusion we can come to is that the emergency generator voltage output raised to a level that turned on the braking units, which heated up the resistors, just like a toaster , until the damage occurred. this could have been a lot worse, we only needed to replace the burned braking units, resistors, and melted wiring. luckily the building did not catch fire. it was a 17 story old folks home, they had no elevators for a few days, talk about a pain. there needs to be a circuit that will eliminate this kind of failure, the braking units should only be activated while the car is running and regenerating, not standing still. any ideas