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[aprssig] Snow, Back-feed, Shocking things

Greg D. ko6th_greg at hotmail.com
Tue Feb 9 04:06:32 UTC 2010


Not to keep the discussion going, but I haven't seen this morsel of input...

I am told that a Transfer Switch also is constructed to prevent an arc-welded contact from keeping the circuit live.  With standard circuit breakers (like the 100A "mains" breakers in a typical home panel), there is a small but non-zero chance that opening the breakers will not actually open the circuit due to a failed contact.  There is pretty much no way to detect that this has occurred, until you've killed someone upstream.

Greg  KO6TH


> From: k7ftp at k7ftp.net
> To: aprssig at tapr.org
> Date: Mon, 8 Feb 2010 15:14:28 -0700
> Subject: Re: [aprssig] Snow, Back-feed, Shocking things
> 
> From: "Tom Mandera" <tsm1 at tmcom.com>
> > How is a transfer switch significantly different from disconnecting the 
> > main breaker (which could have failed and be passing electricity even when 
> > off, but uncommon) before plugging on the backup power?
> 
> A real transfer switch employs a BREAK BEFORE MAKE architecture.  Either the 
> generator is connected to the circuit, nothing is connected to the circuit, 
> or the utility is connected to the circuit.  Really a DPTT with a center off 
> position.
> 
> A real transfer switch connects between the house circuit breaker panel and 
> the circuits that can be generator powered.  When they are properly 
> installed, they guarantee that you can't backfeed the utility and 
> potentially cause problems (or death).
> 
> Here is a link to an installation of a real transfer switch.
> 
> http://www.empreputah.com/gentran.htm
> 
> Personally, I believe that we have way too many laws and restrictions in 
> this country, but that there are things that are SMART to do.  We shouldn't 
> legislate them, but our elected officials (and the appointed ones they 
> select) love to try to legislate away all stupidity and carelessness, and 
> they usually legislate away all of the freedom in the process.
> 
> But like I said - there are things that are SMART to do.  Electricians don't 
> use MALE plugs as power SOURCES because of the exposed contacts.  FEMALE 
> receptacles are used for SOURCES because the contacts are protected - 
> reducing the likelihood of someone getting shocked.  The setup that Bob has 
> created is acceptable as long as BOB is the one working with it and he 
> ALWAYS does it correctly.  If he doesn't, or if someone else is working with 
> it, the likelihood of a problem is GREATLY increased.
> 
> Let's compare this with the rules of firearm safety. 
> http://www.jeepgunner.com/gunsafety.htm
> 
> TREAT EVERY FIREARM AS IF IT IS LOADED
> 
> NEVER ALLOW THE MUZZLE TO POINT AT ANYTHING YOU ARE NOT WILLING TO DESTROY
> 
> KEEP YOUR FINGER OFF OF THE TRIGGER UNTIL THE FIREARM IS POINTED AT A TARGET 
> YOU ARE PREPARED TO SHOOT
> 
> If these rules are always followed, then the likelihood of injury or death 
> in the event of a malfunction is little or none.  If any one of the rules is 
> ignored, the likelihood goes up.  If two of the rules are ignored, they go 
> up more.  It's the same with this situation.
> 
> There is a more practical standpoint on this.  When I lived in Oregon, the 
> local power utility would not start to work on the lines in an area if there 
> was any sign of a generator in operation until someone had verified that the 
> generator was incapable of being connected to a home - or that a transfer 
> switch of the type I linked to above was installed and being used.  If they 
> found a setup like what Bob is using, they would not work on the lines in 
> that area until it was disconnected and the cable used was "safed".  Bob 
> might have some very angry neighbors that are waiting for their power to be 
> restored when they find out that he is the one holding it up while he argues 
> with the utility company.  While his setup might be safe as long as he is 
> the one that sets it up and he does everything right, there is enough 
> potential for issues that they would be within their abilities under local 
> laws and codes to demand that he disconnect it and keep it that way.
> 
> Just as a telco can disconnect any phone line which has problem-causing 
> equipment attached, the power utility can do the same thing.
> 
> In this case, there is a legal and affordable way to avoid the issue.  I'd 
> recommend it.
> 
> Jim - K7FTP
> 
> 
> 
> 
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