Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!utgpu!water!watmath!clyde!rutgers!seismo!rochester!kodak!ornitz
From: ornitz@kodak.UUCP
Newsgroups: sci.electronics
Subject: Re: Physiology Grounding (and GFI's)
Message-ID: <842@kodak.UUCP>
Date: Wed, 6-May-87 09:19:57 EDT
Article-I.D.: kodak.842
Posted: Wed May  6 09:19:57 1987
Date-Received: Fri, 8-May-87 01:48:17 EDT
References: <573@neoucom.UUCP>
Reply-To: ornitz@kodak.UUCP (barry ornitz)
Organization: Eastman Kodak Co, Rochester, NY
Lines: 28
Keywords: grounding, shielding, ground fault interrupters, GFI
Summary: GFI's may not work here.

Ground fault interrupters do not trip by sensing current in the Green wire;
they trip by detecting the difference in current between the hot and neutral
wires.  Leakage from the hot wire (Black) may be to externally grounded
objects, thus sensing current in the ground wire (Green) does no good.  In
Galen's situation, the ground wires are actually lifted from ground by the
impedances of the wiring.  Current returning in the neutral line will create
a voltage drop in the wiring. Connecting the ground to the neutral at the
socket will impose this voltage on any equipment connected to the ground wire.
Touching this equipment and another, perhaps better, ground such as a cold
water pipe could create a shock hazard which would not be detected by a GFI.
I suggested to Galen that he use an Ultra-Isolation transformer with the
equipment ground not being connected to his neutral but to an external ground.
Since neither side of the isolation transformer secondary is grounded, there
should be an added measure of safety.  With the proper use of differential
inputs on amplifiers, etc., most of the noise problems can be eliminated but
the safety problem will remain unless the neutral and ground line are connected
only at the actual "ground" location (practically speaking - the service
entrance where the physical "ground" connection is made).

 -----------------
|  ___  ________  |
| |  / /        | |  Dr. Barry L. Ornitz   UUCP:...!rochester!kodak!ornitz
| | / /         | |  Eastman Kodak Company
| |< < K O D A K| |  Eastman Chemicals Division Research Laboratories
| | \ \         | |  P. O. Box 1972
| |__\ \________| |  Kingsport, TN  37662       615/229-4904
|                 |
 -----------------