chassis isolation, contrary to UL1740?

[Al Skierkiewicz]

Jonathon,
There are a variety of issues that your specification is intended to cover that does not apply to the problems encountered in FRC robots. The high current capability of the power supply in either fixed or mobile robot services can allow a significant voltage to be developed should the robot frame not be bonded to a good ground and power supply common. This is based in part on the known failure of fuse components and the developed hazards due to the failure of these protection devices. Entering into these specifications are such documented variables as common skin resistance, breakdown of typical footwear, hazardous voltage levels, etc. all designed to prevent injury to anyone standing near or on a piece of equipment or in casual contact with it.
The deliberate prevention of using the robot frame as a power supply common or current carrying conductor is in direct response to the experience of robot interaction in an FRC event. As the game changes from year to year, there are often severe robot contacts that include arms and other appendages becoming entangled in the opposing robots. It would be possible therefore for an arm to contact the power supply distribution terminal, pre fused or protected, and pass current through both robots when and if the frames should touch. (i.e. the path from positive terminal through arm/appendage to robot frames and back to the negative terminal) By isolating power from the frame, a continuous circuit cannot be made simply by robot to robot contact. Not only does this practice prevent damage to control components, it minimizes fires and battery damage on the field. Remember that two robots entangled as described above, would continue to complete a maximum current circuit even if the robots were disabled.
This brings up an interesting issue with the new control system as the NI CrIO case is connected to power supply common to be in compliance with specifications you have described but puts FRC robots at some risk not previously encountered. I am sure that FIRST engineers are working on this problem as we speak/write.