[Elecraft] [OT] Grounding negative side of power supply?

[David Woolley (E.L)]

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
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