[Elecraft] Was Grounding negative side of power supply? -CORRECTING A SERIOUS ERROR

[Jim Brown]

On Thu, 21 Jan 2010 14:02:58 -0500, Joe Subich, W4TV wrote:

>While the Neutral (the white wire in the US three wire power 
>cable) must be bonded to ground at the service entrance and 
>nowhere else, by code the Neutral must ** NOT ** be bonded to 
>the case/chassis of any equipment (e.g., white should never 
>be connected to the case) so the neutral is not at issue here. 

>However, the SAFETY ground (green wire/round pin) is also 
>bonded to ground at the service entrance - and in most 
>residential installations ONLY at that point.  

That's tradition, and common practice, but there is nothing in 
NEC to discourage additional earth connections to the  ground 
(the green wire). 

>It is this situation, where the safety ground (chassis) and 
>the shield of the coaxial cables (also connected to chassis) 
>are at different potentials that is potentially unsafe. 

No, it is bonding of neutral to the EQUIPMENT GROUND (in that 
equipment) that is the problem, because it allows return current 
to divide between neutral and equipment ground and any other 
conductors that the equipment ground is bonded to. For example, 
the return current might flow on steel building structure, or in 
low voltage wiring (shields of audio or video cables, etc.), or 
on metallic plumbing pipes. It makes it less likely that a fuse 
will blow in the case of a fault, AND it spreads out the magnetic 
field rather keeping it contained between the phase (hot) and 
neutral conductors. There is a tutorial drawing of this in the 
Ham Interfacing tutorial, and also in the Power and Grounding 
tutorial. 

The connection of power system ground wiring (the equipment 
ground, also called the green wire) to earth at multiple points 
is highly desirable. As you noted, it helps all the wiring "rise 
and fall together" in the event of a lightning event, thus 
minimizing the voltage between interconnected equipment. 

That is, of course, a double edged sword, since currents will be 
induced in loops by magnetic coupling, but authorities agree that 
having the building rise and fall together is far more of a 
factor than induced current. 

73,

Jim Brown K9YC