Re: gEDA-user: powermeter board, with less ground planes :-)

[Joerg <joergsch@xxxxxxxxxxxxxxxxxxxxx>]

DJ Delorie wrote:
>> Nice job. The only thing left is to decide what to do with the circuit 
>> ground. Wherever safety regs permit I always run that straight to all 
>> the bolts. Whatever you do never leave that floating about. Same for the 
>> enclosure. Of course if the enlosure is plastic this doesn't matter.
> 
> On the furnace board, chassis ground and circuit ground were separate,
> with a large resistor and small capacitor connecting them.  I didn't
> trust all the other wiring in the furnace to be properly grounded
> (although, in theory, it's all isolated anyway) so I kept it all
> isolated, but the enclosure is all metal so I wanted some connection.
> 
> On this one, since the board goes inside a circuit panel box, I'm
> thinking of again keeping it all isolated, although ground is
> connected back through the USB to the computer doing the monitoring,
> so it's not floating.  Non-metallic container, if any (personal use :).
> I'm much more worried about accidental shorts than about floating
> grounds (the sensors are all isolated too).  Maybe I'll bolt sheets of
> clear plastic on the top and bottom of the board to protect it.
> 

Be careful. If for some reason the USB ground comes off and that's the 
only ground it'll be anyones guess where any capacitively coupled 60Hz 
will go. If it picks the data lines ... bzzzt ... poof. At least there 
should be some kind of bleeder.

If by circuit panel box you mean the breaker box (or a sub-panel) 
legally you aren't supposed to do that AFAIK.

[...]

-- 
Regards, Joerg

http://www.analogconsultants.com/

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