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Subject: Re: Orleff on 110V safety on lx200
From: h h funston
Reply To: mapug@shore.net
Date: Sun Oct 22 05:55:12 1995

>I would like (as a Brit living in the states the past 14 years) make a few
>comments concerning Brandon Jones' statement about U.S. mains systems having
>a center-tap to earth at the power station so that the maximum voltage to
>earth can only be 55 volts ac. This is not correct.
>
>U.S. main voltages of +/- 110 V ac (bi-phase) are provided locally to each
>home or group of homes by a step-down transformer (from 13 kV) with a
>secondary center-tap output. The neutral goes to the center-tap and so does
>the local power company ground. The voltage between the two "hot" outputs
>is 220 V. The maximum voltage to earth is 110 v not 55 volts.
>
>Also, because of the "peculiar" ground system in North America, usually a
>substantial current does flow through the earth connection (safety ground
>in case the neutral line gets broken) in the home back to the transformer's
>center-tap. This "net" current is responsible for 1/r magnetic fields
>around the cold water line in many parts of the states and the 1/r field
>around the service drop. It is the greatest source of long range magnetic
>fields in most American homes, and one day may be shown to be a health
>hazard.
>
>For more details, see my "Forum" letter in the April 1995 issue of IEEE
>Spectrum.
>
>Sorry for the off-subject comments.
>
>
>Stuart
>
>
>
>Dr. Stuart A. Kingsley
>ETI Photonics
>Director, The Columbus Optical SETI Observatory
>Optical SETI BBS: (614) 258-1710
>
>545 Northview Drive
>Columbus, Ohio 43209-1051
>United States.
>Tel: (614) 258-7402
>Fax: (614) 258-7459
>CompuServe: 72376,3545

Stuart-
You get my vote for your useful input from eye tripple ee. It is hardly off
the subject!
Since much of our present amateur astronomic equipment is computerized or
at least electrically operated and/or electronically controlled (and
costly), you have provided vital and fundamental insight into our knowledge
field. I run a voltmeter in-line with power input to my entire observing
system (computers and telescope) as a matter of practice. During our high
desert summer thunderstorms, lightning hits have been known to damage a
transformer's input/output ratio producing (instead of our normal 124 volts
ac) averages in the low 80's (without producing an outage for the downline
user) which tends to destroy or distort expensive equipment if attempts are
made to utilize such a low voltage.
Everything in my system goes through my UPS, but when the met folks forcast
thunderstorms (and I monitor the weather daily or sometimes more often,
both visually and through Purdue) my entire system gets UNPLUGGED. A
lightning strike can skip through an UPS like it didn't exist!

Thanks again.

Herb Funston
MTFAO, Hereford, AZ