On 2011-02-07 3:01 PM, Don Cox wrote:
> I would think the top priority would be a really good earth (ground).
Hi, Don,
I am not picking specifically on you, but this is so often stated that I
cannot resist explaining the emperor's wardrobe.
Electronics on airplanes and satellites work well without a good earth
ground...
What one really needs is some sort of zero reference grid so that there
are no ground gradients within the space. One also needs to avoid
unbalanced connections in case there is some gradient across the
reference plane/grid.
The only reason a facility needs to be grounded is for when you are
entering it or leaving it. Imagine how much it would hurt if the
sidewalk was at 0V and the building was at 1000V and you stepped across.
Downright shocking, I say!
The AES compendium on grounding that Neil Muncy was involved with about
20 years ago is a must. This shattered many earlier belief systems.
Neil and I still don't fully agree on some of the grounding
philosophy--for example, IG can be as much of a problem as a cure, and
the IEEE Emerald Book says so.
> IEEE Emerald Book STD 1100-1999 IEEE RP for Powereing and Grounding
> Electronic Equipment
>
> 8.5.3.2. Isolated Ground Configuration p 322
>
> This type of equipment grounding configuration is only intended to be
> used for reducing common-mode electrical noise on the electronic
> equipment load circuits as described in the NEC. It has no other
> purpose and its effects are variable and controversial. The use of the
> traditional orange-colored IG receptacle for the express purpose of
> identifying computer grade power is not allowed per the NEC. If
> unacceptable electromagnetic interference is found to be active on the
> circuit, an IG receptacle circuit may be considered as one potential
> mitigation method. Robust design of the electronic load equipment for
> immunity to disturbances on the grounding circuit is another method.
> Particularly for distributed computing and telecommunications
> electronic loads, using optical signaling interfaces reduces
> susceptibility to disturbances on the grounding circuit
Anyway, one cannot fight success when grounds improved something, but
often it is not for the reason suspected.
Another great resource are the books authored or co-authored by Ralph
Morrison. He was part of the AES grounding tour.
Cheers,
Richard
--
Richard L. Hess email: [log in to unmask]
Aurora, Ontario, Canada (905) 713 6733 1-877-TAPE-FIX
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