On Tue, 6 Sep 2005 11:47:41 -0400, "Chris" wrote:


"SQLit" wrote in message
...

"Ignoramus25850" wrote in message
...
I have been playing with using relays of various kinds, as well as
contactors. I already built 2 phase converters, and a remote switch,
for instance. I have a few 90A and 75A contactors and solid state
relays and mag starter buttons and whatnot.

Here's what I have been thinking about. I have a 7 kW Onan DJE
generator that I have for emergencies. I want it to power my entire
house in emergencies (I know that I cannot run AC and some other
devices while under generator power).

It is expensive and painful to install a transfer switch. I want to
make something easier and cheaper to power the house in case of
emergencies, while at the same time preventing backfeeding.

I can, instead of a transfer switch, build a system that includes a
contactor, a mag starter, and a relay that only closes the main
generator contactor when the main circuit breaker is in the OFF
position.

It would work something like this. There will be a mechanical device
and a switch such that the switch could be closed only when the main
breaker is off. When the main breaker is on, the switch could not be
closed.

Where I live the utilities require physcial and electrical interlocks.
Most residential panels do not lend themselves to a physcial interlock.
Square D is the only one that I know of that has a physical interlock
between the main and another breaker.
Then comes to the issue of the equipment being service rated. Then comes
UL
listings.
A contactor/motor starter off the shelf I do not believe is service rated.


There will be a DC circuit, powered by a 9V battery, that would be a
signal input to a solid state crydom relay. The power contacts of the
relay would be in series with the power from generator. When the relay
is closed (only when the mains breaker is open), and a START button is
pressed on the start/stop switch (like ones used for mag starters),
the main contactor would close. The STOP button interrupts input to
the contactor, causing it to open. Turning the little switch near the
main breaker off would also interrupt the circuit, opening the
contactor.

This seems to be a very fool proof system. I can build it in 30
minutes, except that I would need more time to fabricate a mechanical
switch opener/closer.

One piece of advice. I am not seeing it in your description, but I might be
missing it. Do you have a plan for seeing that the incoming power from the
street is back on?

I only mention this as I once had a friend do something similar, and failed
that part. Worse yet, he had to get into his car to drive by a few
neighbors to see if power had been restored. Even worse yet he had to drive
by two of them as they had generators. Remote area it was.
On my brothers recreational property the meter is at the road (with a
disconnect and main breaker) and there is a red pilot lite on the back
of the service box that tells him power is on. His transfer switch is
back at the buildings. When the light is on, he knows the grid is up.