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

[Joe Subich, W4TV]

Jim, 

> 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.

Bonding the neutral to the equipment ground (chassis) in the 
equipment is a violation of both NEC and UL standards.  Both 
power conductors (hot/black and neutral/white) must be isolated 
from the chassis/equipment ground.  

Per NEC, the neutral should be grounded exactly one place - 
at the power entrance.  Connecting neutral to the chassis, 
and via the chassis to the safety ground, would violate NEC. 
In addition connecting neutral to the equipment chassis could 
(would?) result in improper operation of any GFCI on that 
circuit. 

The issue of multiple grounding is entirely separate from 
"grounding the neutral." 

73, 

   ... Joe, W4TV 
 


> -----Original Message-----
> From: elecraft-bounces at mailman.qth.net 
> [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Jim Brown
> Sent: Friday, January 22, 2010 3:15 AM
> To: Elecraft List
> Subject: Re: [Elecraft] Was Grounding negative side of power 
> supply?-CORRECTING A SERIOUS ERROR
> 
> 
> 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
> 
> 
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