RE: [CAD_CAM_EDM_DRO] Re: Remember Mr. Bill's servo lite?

Again, you are only saying the "conventional" stuff, Jeff. I don't mean to pick on you, but can you tell me why a direct path from mains to earth is more dangerous than a magnetically coupled path from mains to earth?

I can't see any reason why 100V, say, should be more dangerous whether it is through a transformer or directly coupled to the mains.


Andy Wander

-----Original Message-----
From: CAD_CAM_EDM_DRO@yahoogroups.com [mailto:CAD_CAM_EDM_DRO@yahoogroups.com] On Behalf Of Jeffrey T. Birt
Sent: Saturday, January 14, 2012 4:13 PM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: RE: [CAD_CAM_EDM_DRO] Re: Remember Mr. Bill's servo lite?

Let's stop and consider what a transformer is and why it works. A
transformer is two coils of wire wound around a common ferrous core. There
is no direct electrical connection between these two coils, that is current
(electrons) do not flow from the primary coil to the secondary coil. When
current flows through a wire a magnetic field is produced around the wire.
In the case of AC current, since the current is always changing the magnetic
field is always changing. It just so happens that a voltage in induced on a
wire when it is in the presence of a changing magnetic field. So here we
have out transformer, two coils of wire that are only coupled by a magnetic
field, thus they are isolated from one another.



The secondary side of a transformer has no direct connection to the primary
so if you measure from one side of the primary to the secondary you won't
see a voltage there. The voltage is 'across' the secondary. A 'variac' is an
autotransformer, take a look here:
http://en.wikipedia.org/wiki/Autotransformer . As you can see there is a
direct electrical connection between the primary and secondary sides (no
isolation). In essence your machine is directly hooked to the mains. If some
electrical wire frays and touches your machine frame (or you!) now you have
a direct path from mains to earth, a very dangerous situation.



Hope that helps



Jeff Birt

Soigeneris.com



From: CAD_CAM_EDM_DRO@yahoogroups.com
[mailto:CAD_CAM_EDM_DRO@yahoogroups.com] On Behalf Of Andy Wander
Sent: Saturday, January 14, 2012 1:18 PM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: RE: [CAD_CAM_EDM_DRO] Re: Remember Mr. Bill's servo lite?





That;s what I don't get, and nobody seems capable of explaining it-they just
say "it is".

Take 2 scenarios:

1) A couple of wires plugged in to an AC outlet at 120VAC. One wire will be
"grounded", while the other wil be at 120VAC above ground.

2) A 120VAC isolation transformer, with the primary plugged in to the same
AC outlet, and the wires attached to the secondary.

Why is #1 necessarily more dangerous? I could think up scenarios, especially
if one side of the secondary is NOT grounded, where #2 would give more
chance of a dangerous electrical shock. But let's assume one side of the
secondary is #2 IS grounded. Why is it safer to have the isolation
transformer?

Andy Wander






[Non-text portions of this message have been removed]



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