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Switch over power
By RobD, Section Homebrewed Electricity Posted on Sat Nov 22nd, 2003 at 03:58:02 AM MST
Has anyone built a power switch for their main box?

I'm looking to build a power switch to flip over to my batteries when the power fails. I've never seen one. How are they set up? Does the main fuse come out and a plug go into it to xfer the line to a switch box?
What's the code and where do you get the parts?
Thanks,
RobD

Switch over power | 7 comments (7 topical, 0 editorial)

Re: Switch over power (none / 0) (#1)
by Electric Ed on Sat Nov 22nd, 2003 at 05:45:48 AM MST
(User Info) http://www.electric-ed.com

Codes require a double throw transfer switch to prevent the stand-by power source from ever getting into the utility lines. The utility transformer would step it up to a voltage that could be dangerous to utility linemen.

There are liability/insurance issues if the installation is not done to code.

Example of a generator/transfer switch below.

Electric Ed

Re: Switch over power (none / 0) (#2)
by windstuffnow (elenz(at)windstuffnow(dot)com) on Sat Nov 22nd, 2003 at 07:05:46 AM MST
(User Info) http://www.windstuffnow.com/main

Just out of curiosity... If you break or pull the mains from the house's main panel box and tie a generator to the same box through separate mains, is there any way to feed the utility line? If not what about the neutral line? Any possibility of feeding back on the neutral?

Windstuff Ed

Have Fun! Windstuff Ed
[ Parent ]

Re: Switch over power (none / 0) (#3)
by Electric Ed on Sat Nov 22nd, 2003 at 11:08:08 AM MST
(User Info) http://www.electric-ed.com

What you describe is safe enough, it's just that the inspection authorities do not accept transfer schemes that rely on an individual REMEMBERING to open the main.
Because they deal with the public they require it to be "idiot" proof, and usually with good reason.

You wouldn't believe what some folks will do. :-)

There normally wouldn't be any "feed back" on the neutral. The reason my example sketch shows a three-pole transfer switch is to deal with a grounding issue. If the generator neutral is NOT bonded to the frame, a two-pole transfer switch would be required, as shown below.

Electric Ed

[ Parent ]

Re: Switch over power (none / 0) (#4)
by windstuffnow (elenz(at)windstuffnow(dot)com) on Sat Nov 22nd, 2003 at 01:39:13 PM MST
(User Info) http://www.windstuffnow.com/main

Couldn't you take two single throw boxes, mount them handle to handle and end up with a very inexpensive power transfere system? Going handle to handle puts one box upside down and the other right side up. bolt the handles together, one breaks the connection to consumer line and the other connects the gen to it. Much cheaper than those Gen boxes and allows you to use a common main panel.

Mine is set up on the "remember" theory right now but I'm looking for ways of meeting code cheaper...

Have Fun
Windstuff Ed

Have Fun! Windstuff Ed
[ Parent ]

Re: Switch over power (none / 0) (#5)
by Jerry on Sat Nov 22nd, 2003 at 09:49:49 PM MST
(User Info) http://www.dplusv.com/Photo-03.html

Hi Guys.
This is what I've done. I went to the big box home improvement store and picked up a metal switch box that has room for 9 lite switches, picked up 9 double pole sigle through light swiches. The are the type wall switch that lets you turn of one lite in a room at two locations. By this door or by that door. One lite 2 switches.

I sellected 9 circuts in the house. These circuts are wired to the sellecter part of the switch. Now I have 2 terminals left over. One term. is wired to the circut breaker where the Utility power is coming from and the other is wire to my inverter. However on each one of these I've wired a seperate circut breaker for safty.

I works realy slick I can sellect any circut I want or all. Home power or grid power just flip a switch. I'm going to do the rest of the panle this way. However this is only for 120 volt use. Thats the CAUTION here.
For my apliction thats all I need. And there is no danger of sending power back to the grid.

I think I did this hole project for less than $20. The big box store whanted $200 for there switcher box that dose the same thing.
It works good for me. Use at your own discresion?

JK TAS Jerry

Airheads Page

[ Parent ]

Re: Switch over power (none / 0) (#6)
by RobD on Sun Nov 23rd, 2003 at 02:37:03 PM MST
(User Info) http://www.dsgnspec.com

Thanks for the help everyone.
Nice idea Jerry!
WS Ed. I'm going to use the main fuse as a 'breakout' to feed the three terminal relay. I like the three terminal relay idea and I may build a sensor to switch it over when the power fails (which happens a lot up here) like an UPS configuration. I'll check with my rural co-op to see what they say first.
Thanks again everyone,
RobD

Re: Switch over power (none / 0) (#7)
by Joseph Turrisi on Sun Nov 23rd, 2003 at 06:05:17 PM MST
(User Info)

It shouldn't be two hard to build your own switch but I wouldn't recommed it. If it is not UL appove and installed according to the national electric code, your homeowners insurance will have an excuse not to pay out if some thing bad happens like a fire or electrical shock.

Switch over power | 7 comments (7 topical, 0 editorial)

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