Jim Brown wrote:
> On Fri, 31 Jul 2009 16:59:36 -0700, jimlux wrote:
>
>> All you can do is arrange your gear so that any such "loop" currents
>> don't flow through the delicate insides of the boxes.
>
> Yes. Bonding shields to avoid "pin 1 problems" is an important component
> of this. See http://audiosystemsgroup.com/publish for extensive
> discussions of this. There is a similar problem with bonding of the green
> wire within equipment. It SHOULD go to the shielding enclosure, not
> "signal common" on the circuit board.
>
> Another issue is the use of shunt-mode surge suppressors on branch
> circuits, which can blow up a lot of interconnected gear,
>
Or internal equipment design that results in chassis transients
propagating to signal common.
Though.. for hams, the general advice I'd have is, do a reasonably good
job of thinking through where the fault and transients go, and protect
against them, and carry enough insurance or cash in your wallet to
replace stuff when it fails. Most hams aren't really doing a 24/7 six
9's reliability comm situation.
That's sort of the difference between consumer equipment and industrial
or professional equipment. IN a consumer box, the power might be from a
wall wart, and the signal common is connected to chassis ground. In a
industrial box, there will probably be a three prong plug, a metal box
that's connected to the third prong, and the signal lines and commons
will be isolated from the chassis. They make insulated bushing BNC
connectors for a reason. Pin 7 (signal ground) on an RS-232 DB-25
connector isn't chassis ground (that's pin 1 and the shell) for a reason.
The electrical code is a good starting place for general wiring
practices. The bonding and interconnection rules didn't just come out of
thin air, but are the result of decades of experience and are updated as
more things are known and as usages change (for instance, there was a
big change a 20 years or so ago with requiring bigger neutral conductors
in 120/208 3 phase Wye, because of the use of switching power supplies,
particularly in PCs)
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