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
>
>
> -----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 2:09 PM
> To: CAD_CAM_EDM_DRO@yahoogroups.com
> Subject: RE: [CAD_CAM_EDM_DRO] Re: Remember Mr. Bill's servo lite?
>
> The 'lack' of isolation is what makes it dangerous. Would you leave bare
> wires plugged into the mains just lying out in the open in your shop? I'm
> guessing nobody would even though it won't hurt you unless you touch it. Not
> having any isolation from the mains is almost as bad.
>
>
>
> 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 12:53 PM
> To: CAD_CAM_EDM_DRO@yahoogroups.com
> Subject: RE: [CAD_CAM_EDM_DRO] Re: Remember Mr. Bill's servo lite?
>
>
>
>
>
> But what is it that makes the Variac more dangerous than an
> identical-voltage isolation transformer?
>
> 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 David G. LeVine
> Sent: Saturday, January 14, 2012 12:46 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?
>
> On 01/13/2012 09:24 PM, Andy Wander wrote:
>> The gist of the explanation that I got was, "There's no galvanic
> isolation", and "If you can't see that it's dangerous, I'm not going to
> bother telling you why". People got very upset and angry at me, but nobody
> seemed to be able to explain the danger.
>
> Okay, let's step back and then forward.
>
> I have been in a building where the water pipes went to more than 13.8
> KV above ground, luckily no one was hurt, but if anyone had touched the
> pipes, they could have been fried because the wooden floors still have a
> little conductivity due to humidity, until the wood starts to char.
>
> This is an extreme example (and _/*can't*/_ happen in a home.) The
> building was a big industrial building with 13.8 KV power coming in.
>
> Let's start with grounding and ground loops. When two or more grounds
> have multiple references, currents can (and probably will) flow between
> the ground references. These circulating currents often lead to
> voltages across the ground system. These are generally small (a few
> volts or less), BUT when the signals you are trying to use are only 3
> Volts, this noise can be a big issue. Of course, when a many kiloampere
> impulse happens, lots of stuff goes wrong (lightning strikes, for example.)
>
> Safety is not an issue, we use double insulated tools all the time and
> they do not cause many deaths. However, unless you are following all
> the protocols, the risk is very high. If you can come in contact with
> the "hot" lead from the variac, you can easily be injured or killed, if
> you follow all the protocols, you never will. Do you even know all the
> protocols? I bet you don't.
>
> Let's use firearms as an example. When used by a skilled, competent
> user, following the safety protocols, the accident rate is simply
> amazing, nearly zero. But you hear about people who don't follow all
> the protocols and incompetent users dying or accidentally killing others
> on an all too regular basis. I have had two VERY skilled friends blow
> holes in their homes due to firearms accidents. They did not follow all
> the protocols and got careless. Since they were still following most of
> the protocols, no one was hurt, but that is why the safety protocols
> seem to be way too restrictive, violate one and you wind up surprised,
> violate too many and someone winds up hurt or dead.
>
> High energy tools (yes, weapons are tools too) are inherently dangerous,
> that is why the protocols are in place.
>
> Low voltage signaling can always be overridden by high voltage noise.
> Look at lightning strikes.
>
> What you are trading off is a safety factor against cost. Many people
> will tell you that having an exhaust leak is not a big deal, and it
> isn't, in the summer on the highway. But in the winter, in a traffic
> jam, it can kill you. In general, a variac will work just fine, but
> sometimes you are at risk, or worse yet, some unknowing person will get
> hurt because you are not following ALL the other safety protocols.
>
> Dave 8{)
>