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[aprssig] Snow, Back-feed, Shocking things

K7FTP k7ftp at k7ftp.net
Mon Feb 8 22:14:28 UTC 2010


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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