gEDA-user: earth ground & EMI

[John Griessen]

DJ Delorie wrote:
>The capacitor in those filters needs to be connected
> to... something.  Normally, I'd just ground them, but I'm going to put
> filters on the power and ground terminals too (unless that's stupid).
> Where do I connect those caps?  

You would only want filters in the ground terminals in the case that ground wire 
went out over open ground and was susceptible to lightning strike transients. 
for the furnace system, some transient suppressors on the power wires should be 
enough.


You usually don't want a reactance against conducting current in your ground 
path.  IOW, don't put filter inductance in series with the wire to building 
ground...Use it as the place to connect to the central star point of your 
board's ground traces.  Then, don't ground anything else by connector shells, or 
other wires to other systems or components of your house furnace system.  Have 
them all connected to the building distribution panel safety ground buss, (the 
bare copper one), and outside the building connect that to a ground rod in the 
earth.

John G

PS  I'm designing a sensor network system right now that DOES have filters in 
series with the ground terminals...   and does have wires running out tens of 
feet over the ground that will pick up common mode spikes when lightning strikes 
nearby...