[TenTec] TT 940 Power Supply

[Bob McGraw - K4TAX]

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 at arlut.utexas.edu>
To: <tentec at 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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