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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