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From: wtm@neoucom.UUCP
Newsgroups: sci.electronics
Subject: Physiology Grounding
Message-ID: <573@neoucom.UUCP>
Date: Tue, 5-May-87 23:34:15 EDT
Article-I.D.: neoucom.573
Posted: Tue May  5 23:34:15 1987
Date-Received: Thu, 7-May-87 06:14:44 EDT
Organization: Northeastern Ohio Universities College of Medicine
Lines: 37


Hi,

Sorry, but I was going to reply to the person from Virgina that
wanted information about grounding in [electro] physiology, but our
system crashed right in the middle of your article, and it
disappeared into the bit bucket in the sky.

If you'll write or call me, I'd be happy to relate some of my
experiences working in a lab doing electrophysiology.  In short, if
you wire everything up as per the manuals for whatever
electrophysiological amplifier you have, the fact that the AC
ground wire is bonded to the neutral lead in multiple places in
your building should not matter.

What you do have to keep in mind is that if your experimental
subject is a person, you gotta gotta gotta gotta gotta use a Ground
Fault Interrupter (GFI) circuit breaker right at the end of your
recording equipment's line cord.  This will detect any current that
accidentally flows in the GREEN ground lead, indicating that your
subject is in danger of being electrocuted.  Most GFIs trip at a 10
mA current flow in the GREEN wire.  They'll trip within 16 mS of
sensing the fault.  10 mA flowing in your victim, err ah subject
won't fell real good, but should be harmless if it happens.

The easiest way to add a GFI is to replace the wall plug in your
lab with a GFI receptacle.  Most hardware stores have them for $15
to $20.  The expense is well worth it to avoid the possibility of
facing a technical malpractice suit!  The hard part will be
getting your physical plant staff to appreciate the import of
having a GFI and installing it for you.

Bill Mayhew
Division of Basic Medical Science
Northeastern Ohio Universities' College of Medicine
Rootstown, OH  44272  USA    phone:  216-325-2511
(wtm@neoucom.UUCP  !cbatt!neoucom!wtm)