Whenever I'm working in labs, I have always disconnected the +V terminal first because I've always been taught powering a chip without a ground is dangerous and likely to blow the chip. I've also experienced that happening so I'm pretty sure it's true.
However, the other day I was messing around in my car and long story short the battery died. I was instructed to disconnect the ground first because if I was disconnecting the +V and accidentally shorted it to a piece of metal the circuit would still be complete and a whole bunch of amperes would flow and perhaps electrocute me.
Now it seems to me that even with the ground terminal disconnected, if I short the +V of a battery to say the chassis of a car with something like a screw driver, won't current still flow?
Are there other reasons for the reverse paradigm? Any other safety considerations I should be aware? Thoughts in general on this situation?
Best Answer
The main reason for disconnecting the negative terminal on a car battery first is that the whole of the car body is linked to that negative terminal.
Disconnecting it first removes all the possibility of a short between positive and negative without going direct to the battery negative terminal.
For disconnecting individual items within the car, disconnect the positive first as you would with any other device.
As for powering chips without a ground (or \$V_{SS}\$) connection, the power will probably try and find its way out somewhere and yes, could cause problems.
Personally I usually turn off the power supply rather than unplug it live.