view in courier

SERVICE

LINE1 LINE2
120v 120v
o o
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*-------(A)-------*
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* *
\ DISCONNECT \
\ \
* *
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o o

LOAD

o o
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--- C --- C
--- ---
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| *---------*---------*
| | | |
| | | |
| | --- A --- B
| | --- -/-
| | | |
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| | (B) (C)
| | | |
| | | |
| | --- ---
| | - -
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o GENERATOR o


A is a mercury relay with a 240vac coil.
B is a N.C. 120vac coil with 30amp contact.
C is a dpst 120vac coil with 90amp contacts

When the disconnect is ON and the service is either ON or OFF,
* the generator is isolated from service feed
* the generator cannot backfeed into the grid

When the disconnect is OFF and the service is ON
* the generator isolates from the load

When the disconnect is OFF and the service is OFF
* the generator is connected to the load

The generator can't work or be damaged unless the disconnect is OFF.

I designed this circuit around some parts I had. The disconnect is in the
breaker box.