The safety problem is that, with typical ham radio equipment, that negative connection is connected to exposed metalwork, e.g. on the K2, the microphone socket, bezel screws and headphone socket on the front panel, any morse key and the multiple sockets on the back panel. The paintwork, also, isn't designed for electrical isolation.
If there is a fault in the power supply transformer, these can become hot to AC; a Class II power supply addresses this (most amateur radio supplies are not Class II - any that has an earth wire is not Class II). If the rig is grounded to the real earth, electrical faults, or lightning can produce a dangerous voltage between it and other metalwork, which should be connected to mains earth according to your NEC/Building Regulations; ensuring that there is no real ground connected to the rig addresses this one. It doesn't, of course have to be the negative side; there is no absolute rule against positive "earth" systems, it is just that valves and current generation semiconductors are naturally negative "earth" devices. The original, alloy junction, PNP transistors favoured positive common systems. Joe Planisky wrote: > Correct, and I agree that the power supply chassis should be connected > to the AC (mains) safety ground. But that wasn't the situation I was > asking about. I was asking whether the negative side of the DC output > should be connected to the chassis. > -- David Woolley "we do not overly restrict the subject matter on the list, and we encourage postings on a wide range of amateur radio related topics" List Guidelines <http://www.elecraft.com/elecraft_list_guidelines.htm> ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
