[H] Serial port voltages and amperages

[Thane Sherrington]

I have a usb to serial convertor that is being blamed for burning up 
a cable to a car scanner (one of those things used in repair shop to 
check the car's computer.)  When I check the voltages on it, I get 
-5V and 28mA.  From my reading, -5V is fine, but I can't find 
anything about mA.  However, if the thing is running 5V and 28mA, 
could it generate enough heat to burn a cable?

T