DIYbanter - View Single Post - Interlock locks to be used in lieu of transfer switch

Ignoramus23720

On 7 May 2007 17:53:42 -0700, wrote:
I suppose that being a somewhat ethical and caring person, and like
the KISS principle (Keep it Simple Stupid), I would have to go with
the tradition 3-pole, 3-position, transfer switch. On these, one
position puts your home on grid power, in the center postion it is
connected to nothing, and in the thrid position it is connected to
your generator.

Only a week or two ago I was running my home on generator power, with
the generator connected to the house with a "suicide cord", and the
master breakers to the house pulled. I went outside and spent some
time talking with the line crew that was replairing the down line in
front of my home, in the rain. Having noticed that I was running a
generator, one of the guys asked me if I was sure that I was
disconnected from the grid. I replied that I knew I was, because the
breaker connecting me to the grid was not only turned off an pulled,
so I could see about 2-3 inches of physical separation.

No problem, he replied to me, and also informed me that the top like
supplying the transformers on my street was an 8,000 volt line. I'm
not a lineman but am an electrical engineer, and would not sleep at
night if I were risking backfeeding a distribution transformer that
stepped the voltage up to 8,000-volts, or even 2,200, no matter how
clever the interlocking arrangement. I am not that desperate to power
my home, and as an engineer I recognize the too frequent failure of
such arrangements, let alone to build one myself. It's not so much the
design of such interlocks, but the failure modes that amateur
designers often fail to take into account, with tragic consequences.

What you did was considerably more failure prone than an interlock
arrangement.

i

Harry C.

On May 7, 7:05 pm, Ignoramus23720 ignoramus23...@NOSPAM.
23720.invalid wrote:
I have this generator:

http://igor.chudov.com/tmp/onan/Diesel/

I bought these interlocks on eBay:

http://cgi.ebay.com/ws/eBayISAPI.dll...m=300106024488

They are actually quite large, the photo does not do them justice.

My plan is to place interlocks so that either the generator's
disconnect is closed, or the main panel breaker is closed, but never
both.

That's what they were designed for, if it is unclear to anyone, I can
explain it in more detail, or see:http://www.kirkkey.com/index.html

I would lock up another key (they are keyed alike) in my safe so
that its use cannot defeat this system.

I believe that this arrangement fully satisfies the rule that a
mechanical interlock device should prevent both sources of power from
coming in contact.

Any comments?

i