Thanks Stuart for the confirmation.
In my configuration, once I lifted the ground strap between Neutral and
Ground on the OUTPUT of the UPS being the duplex outlets, there is no
continuity between Neutral and Ground. Again this is on the OUTPUT of the
UPS and applies to all duplex outlets on that unit. I found that each
duplex outlet did have the strap in place thus I had to remove all of them.
Having done this, my noise dropped noticeably.
Now, on the input side of the UPS, yes at the breaker panel for the house
the Neutral and Ground are tied together. But this is only, or should be
only, at the breaker panel. Thus if one reads resistance between Neutral
and Ground on any duplex outlet they will find or should find continuity.
PLEASE do not try to measure resistance with power applied to any of the
circuits. There may be some notable amount of AC voltage difference,
depending on the IR drop of the wiring and associated with any load existing
on the Neutral.
73
Bob, K4TAX
----- Original Message -----
From: "Stuart Rohre" <rohre@arlut.utexas.edu>
To: <tentec@contesting.com>
Sent: Wednesday, September 03, 2014 2:52 PM
Subject: Re: [TenTec] TT 940 Power Supply
As a follow up to Bob's comment about checking for continuity between
safety ground terminal on an outlet and neutral; it is my understanding
from current codes, written up in electrical trade magazines discussions;
that the neutral is bonded at one place to the safety (green) ground wire,
and that is at the breaker box, presumably at the entry to the facility.
Bonding in the UPS box seems counter to this practice, and certainly
creates a loop between neutral and safety ground.
Often in practice we have found in our lab facility, multiple loops
caused by bonding green safety ground to neutral in multiple boxes that
may exist between the service entry and the ultimate site of the powered
instrument. It caused bad noise problems such that I finally had a
special feed conduit installed that was bonded at its source of power but
was insulated on brackets until it reached the lab needing low noise A/D
wiring. That finally met our noise spec. There was still continuity from
neutral to safety ground, but we controlled where that singular bond was
made.
-Stuart
K5KVH
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