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[Phys-L] Re: Electromagnetism is Only a Theory!!!



The operation of a ground fault interrupter is interesting. Basically
the current on the hot and neutral wires pass through a sensing coil in
opposite directions. If there is a small difference (5 milliamps) in
these currents a comparator senses it and trips the circuit.

The conventional breaker takes 20 A to trip, but only 100 milliamps are
needed to electrocute under some circumstances, so the GFI now is
required for equipment operated near pools.

See http://hyperphysics.phy-astr.gsu.edu/hbase/electric/gfi3.html#c1 for
more info.

Dr. Mark H. Shapiro
Professor of Physics, Emeritus
California State University, Fullerton
Phone: 714 278-3884
FAX: 714 278-5810
email: mshapiro@fullerton.edu
web: http://chaos.fullerton.edu/Shapiro.html
travel and family pictures:
http://community.webshots.com/user/mhshapiro



-----Original Message-----
From: Forum for Physics Educators [mailto:PHYS-L@list1.ucc.nau.edu] On
Behalf Of William Thomas
Sent: Monday, October 31, 2005 12:29 PM
To: PHYS-L@LISTS.NAU.EDU
Subject: Re: Electromagnetism is Only a Theory!!!

Perhaps more faith may have helped?


On 10/31/05, Shapiro, Mark <mshapiro@exchange.fullerton.edu> wrote:

Equipment used in the vicinity of water should include ground fault
interrupters. Even a properly grounded three wire plug may not prov=
ide
complete protection if equipment becomes wet.


Dr. Mark H. Shapiro
Professor of Physics, Emeritus
California State University, Fullerton
Phone: 714 278-3884
FAX: 714 278-5810
email: mshapiro@fullerton.edu
web: http://chaos.fullerton.edu/Shapiro.html
travel and family pictures:
http://community.webshots.com/user/mhshapiro



-----Original Message-----
From: Forum for Physics Educators [mailto:PHYS-L@list1.ucc.nau.edu]=
On
Behalf Of John M Clement
Sent: Monday, October 31, 2005 12:11 PM
To: PHYS-L@LISTS.NAU.EDU
Subject: Re: Electromagnetism is Only a Theory!!!

Does anyone know if the amplifier was properly grounded, or was it
attached using a cheater plug? It is also possible that the wiring
was improper. I discovered a grounded plug in my house where the
ground was actually attached to the hot side by a previous owner. I=
t
had been put in by a "student electrician" who did not screw in the
extra terminal screws. One of the them contacted the ungrounded met=
al
case of the receptacle enclosure. I checked all of my outlets after
that, and rewired most of them. I thought that most churches now us=
ed
wireless mikes except at strategic points such as the pulpit.

As long as the chassis is not live, the mike should not be a proble=
m.
Most PA equipment has both an internal transformer and a grounded
plug so that there should be no possibility of electrocution. I wou=
ld
say either they were using old defective, improperly constructed
equipment, or they defeated the ground.

Even electricians make fatal mistakes, and sometimes it is their
customers who die. Let us reserve judgement until the facts are
known.

John M. Clement
Houston, TX


... physics teachers who play in pop groups might be advised to
touch a microphone to a copper water pipe or other assured groun=
d
before each gig.

Thanks for the heads up. Fortunately for us, we only do "country
western."

--
John "Slo" Mallinckrodt

If I remember my 'Blues Brothers' correctly, it seemed like the b=
and
could
get pretty wet from all the beer thrown at them! ;-)

Rick