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Transfer Switch: prewird vs. Whole House/Subpanel

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Posted by Ignoramus13229 on January 10, 2005, 6:49 pm
As some of you might remember, I own a well working Onan DJE
generator, 7kW continuous.


I will soon start working on setting up a proper transfer switch. I am
now deciding which one.


3400 sq ft house plus finished full basement, 200A service, almost all
slots in the panel taken. A lot of little circuits. (which has its
advantages). Many of these circuits power very small equipment like
lights, phones etc.

The generator will be installed behind the house, very close to the
panel. It will still be on its carriage.

My objective is to do work that can be UNdone if I want to sell the
house. Hence, I would prefer to not do any service entrance type work.

I have, logically, two alternatives.

1. Buy a prewired transfer switch.

2. Add a large subpanel, move all breakers that I want to be on a
generator, there, and insert a transfer switch between subpanel and
main panel.

Note that this would involve also making wire connections in the main
box, since the circuits are terminated in the main box, obviously, but
the breakers will be in the subpanel box. Because of this, I am not
sure if choice 2 is even legal.

Assuming it is, I see some advantages of 2) over 1).

1. Being able to add more circuits due to having an extra subpanel.

2. Being able to power more circuits in case of an outage, and being
able to choose which ones to turn on and off, with breakers.

Any thoughts on this will be appreciated.


Posted by zxcvbob on January 10, 2005, 7:22 pm
Ignoramus13229 wrote:

You might consider hiring an electrician to install a 200A DPDT switch
between your electric meter and your service entrance panel.  Hardwire
the generator to the switch with appropriately big service entrance
cable.  When you move, you can disconnect the generator (to take it with
you) and leave the switch -- it will function as a disconnect for the
house, and the new owners can use it to hook up their generator.

I don't know if this will require any modifications at your service
panel (installing a ground bus and seperating the grounds and neutrals,

You don't want to do this yourself.  I *might* try it myself if I got
permission from the utility company to pull the meter and reinstall it
when I was done.

This is one of those jobs where you really should get a permit.

Best regards,

Posted by Ignoramus13229 on January 10, 2005, 7:28 pm
Bob, do you have an idea how much it could cost (beside the cost of
the switch). I have no clue.


Posted by zxcvbob on January 10, 2005, 7:42 pm
 Ignoramus13229 wrote:

No idea.  Probably a couple of hundred dollars just for the enclosed
switch.  I'm not an electrician, and I've never had occasion to wire a
transfer switch.  There are a lot of subtleties to a job like this --
whether the switch should be fused or not, solid neutral vs. switched
neutral, etc. -- the whole thing needs to be planned out before you
start, otherwise you will cause a lot of complications later, mostly
dealing with proper grounding of the panels and the generator.

You need to get your garage subpanel fixed before you start worrying
about a generator transfer switch.


Posted by Steve Spence on January 10, 2005, 7:47 pm
 We put a 30amp (per leg) auto transfer switch feeding our main panel.
Two inputs, generator, or inverter. Got the switch from
www.backwoodssolar.com for $26.

Steve Spence
Dir., Green Trust

zxcvbob wrote:

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