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Old July 21st 19, 12:23 AM posted to
Phil Hobbs Phil Hobbs is offline
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First recorded activity by DIYBanter: Sep 2006
Posts: 630
Default How the heck does a typical home transfer switch work?

On 7/19/19 12:32 PM, Ron D. wrote:
1. Note that it's a "Transfer Switch" and not an "Automatic Transfer

A Transfer switch is noting but a "BIG Relay" which is designed so
mains and utility power CANNOT be connected at once if a part

Emergency panel

If the generator is too small for the house, then you put the loads
that need power in an emergency on a single panel. (e.g.
refrigerator, sump pump etc)

The "automatic" part might do a number of things such as: 1.
monthly/weekly test 2. monitor oil level 3. Exercise generator or
generator and transfer. 4. make sure utility power is stable before
taking generator offline. 5. Implement cool down phase. 6. The
generator exercise period may top off the battery. 7. Monitor
voltage/frequency 8. manage starting

So, voltage and frequency out of range will prevent transfer. Oil
level will prevent generator from starting automatically.

You may have two sub-panels and a pool. The pool does not get
generator backup. Looks like your missing stuff like fuses. You may
just have a 12 V signal that tells it to transfer. It may or may not
need power to keep it in one position. I did not look at the

My transfer switch is a pair of 30A breakers for the genny and an
aluminum sheet that slides up and down, so that the main breaker and the
genny breakers can never be turned on at the same time.


Phil Hobbs

Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510