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

Hi Jeff:

I appreciate the effort.

But there are a couple of things that don't convince me still.

For instance, to use your analogy, why is the "red" water more dangerous than the un-colored water?

And I don't think it is correct to say beg to differ that you can't get a shock by touching a single wire from an isolation transformer. The chances are good that you will not get a shock, by completing a circuit to ground, but by no means absolute. The output of the "ungrounded" isolation transformer WILL have some potential with respect to ground-and you don't know what it is.



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 11:16 PM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: RE: [CAD_CAM_EDM_DRO] Re: Remember Mr. Bill's servo lite?

Sorry Andy, I'm really trying to be helpful but trying to explain this type
of thing over email is not very effective.

>So you don't count magnetic flux coupling as an electrical path?

>It can cause current to flow, so even if you call it by a different name,

again, what is the difference?



Electrical current is the flow of electrons through a conductor (something
with electrons that are relatively easy to break loose.) Magnetic flux is,
well magnetic flux they are different things. Just because magnetic flux can
induce a voltage (and current) flow does not mean they are the same thing. A
fire will produce heat but fire and heat are not the same thing.



Let's use an analogy to try and make the point more clear.



Let's say you have an engine driven pump that is pumping water from a pond
through a hose, the hose feeds into an impeller, another hose leads from the
housing back to the pond. The water from the pump in turn rotates the
impeller. This is a closed system, let's call this the 'P' side.



You have a second impeller that has hoses that lead two and from a tank,
basically it sucks water from the tank, circulates it through the impeller
housing and discharges it back into the tank. Let's call this the 'S' side.



Now let's say you mechanically couple the two impellers with a shaft. This
means that the engine driven pump which is circulating water on the 'P' side
is, by means of the mechanically coupled impellers, is also circulating
water through the 'S' side.



Now if you dump a couple of hundred gallons of red dye into the pond, the
pond will turn red and you will have red colored water flowing through the
'P' side. Remember that the two side are only connected by the drive shaft
so the 'S' side still has clear water. The two side are isolated so you
can't get red hands by playing with things on the 'S' side.



This is roughly similar to an isolation transformer. Water flowing on one
side causes water to flow on the other side even though they are only
coupled by a shaft, there is now water flowing directly from the pond to the
tank.



A Variac is like a pressure regulator. It reduces the water pressure from
the source pump but provides no isolation. The water from the pump is the
same water flowing through the tank.



Our electrical distribution system is (earth)ground referenced. You have a
ground rod outside your house and a wire leads from the (earth)ground rod to
your electrical panel where it is connected to the (earth)ground bus (and
the (earth)ground bus is also bonded to the neutral bus.) As you know when
you wire your house there are three wires in the cable, 'hot' 'neutral', and
'(earth)ground'. Current flows through hot and neutral while (earth)ground
is there for safety.



If you stick your finger in an electrical outlet and touch the hot terminal
you will be shocked because your body will provide a current path to
(earth)ground. Now let's say you plug an isolation transformer into that
outlet and touch one of the wires on the secondary side. You won't be
shocked because the secondary side is isolated from the primary side; there
is no electrical connection between the primary and secondary sides. If you
touch both wires on the secondary side you will be shocked because your body
is completing a current between them.



I hope that helps



Jeff



From: CAD_CAM_EDM_DRO@yahoogroups.com
[mailto:CAD_CAM_EDM_DRO@yahoogroups.com] On Behalf Of Andy Wander
Sent: Saturday, January 14, 2012 8:57 PM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: RE: [CAD_CAM_EDM_DRO] Re: Remember Mr. Bill's servo lite?





But it is NOT clear-at least not to me, Jeff. So you don't count magnetic
flux coupling as an electrical path? It can cause current to flow, so even
if you call it by a different name, again, what is the difference?

I am not saying it is ok to use a Variac-but I am always amazed by the
vociferous arguments of those who can't really back them up.

If you can explain why it is dangerous, please do. But just saying "I can't
make it any clearer" doesn't help me understand.

Andy Wander

-----Original Message-----
From: CAD_CAM_EDM_DRO@yahoogroups.com
<mailto:CAD_CAM_EDM_DRO%40yahoogroups.com>
[mailto:CAD_CAM_EDM_DRO@yahoogroups.com
<mailto:CAD_CAM_EDM_DRO%40yahoogroups.com> ] On Behalf Of Jeffrey T. Birt
Sent: Saturday, January 14, 2012 6:37 PM
To: CAD_CAM_EDM_DRO@yahoogroups.com
<mailto:CAD_CAM_EDM_DRO%40yahoogroups.com>
Subject: RE: [CAD_CAM_EDM_DRO] Re: Remember Mr. Bill's servo lite?

There IS NO ELECTRICAL PATH from the isolated secondary to earth ground!
That is the whole point. I do not know how much more clearly it can be said.

Jeff Birt

Soigeneris.com

From: CAD_CAM_EDM_DRO@yahoogroups.com
<mailto:CAD_CAM_EDM_DRO%40yahoogroups.com>
[mailto:CAD_CAM_EDM_DRO@yahoogroups.com
<mailto:CAD_CAM_EDM_DRO%40yahoogroups.com> ] On Behalf Of Andy Wander
Sent: Saturday, January 14, 2012 5:04 PM
To: CAD_CAM_EDM_DRO@yahoogroups.com
<mailto:CAD_CAM_EDM_DRO%40yahoogroups.com>
Subject: 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%40yahoogroups.com>
<mailto:CAD_CAM_EDM_DRO%40yahoogroups.com>
[mailto:CAD_CAM_EDM_DRO@yahoogroups.com
<mailto:CAD_CAM_EDM_DRO%40yahoogroups.com>
<mailto:CAD_CAM_EDM_DRO%40yahoogroups.com> ] On Behalf Of Jeffrey T. Birt
Sent: Saturday, January 14, 2012 4:13 PM
To: CAD_CAM_EDM_DRO@yahoogroups.com
<mailto:CAD_CAM_EDM_DRO%40yahoogroups.com>
<mailto:CAD_CAM_EDM_DRO%40yahoogroups.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%40yahoogroups.com>
<mailto:CAD_CAM_EDM_DRO%40yahoogroups.com>
[mailto:CAD_CAM_EDM_DRO@yahoogroups.com
<mailto:CAD_CAM_EDM_DRO%40yahoogroups.com>
<mailto:CAD_CAM_EDM_DRO%40yahoogroups.com> ] On Behalf Of Andy Wander
Sent: Saturday, January 14, 2012 1:18 PM
To: CAD_CAM_EDM_DRO@yahoogroups.com
<mailto:CAD_CAM_EDM_DRO%40yahoogroups.com>
<mailto:CAD_CAM_EDM_DRO%40yahoogroups.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

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