[Elecraft] (OT) Grounding Mat

[Jim Brown]

On Thu, 25 Mar 2010 10:03:42 -0800, Edward Cole wrote:

>For some test equipment, isolation transformers should be used 
>because they ground circuits that you may not want grounded.  

Aside from the fractured logic in this sentence, power isolation 
transformers, installed per NEC, do NOT isolate the green wire on one side 
from the green wire on the other, because code requires that ALL grounds 
(including all green wires, and the chassis of all equipment) be bonded 
together!  

NEC also requires that the neutral of every transformer secondary must be 
bonded to ground, and as noted above, all grounds must be bonded together. 
So the question is, what, exactly, from a grounding perspective, do you 
expect to gain by using an isolation transformer?  

What the isolation transformer CAN do, IF it has one or more Faraday 
shields, and IF they are properly terminated, is reduce the transfer of 
noise between line and neutral from one winding to the other. Without those 
Faraday shields, the capacitance between windings will still couple most of 
the noise. 

73,

Jim Brown K9YC