Wall Switch Box for the Emergency Power Distribution System
by Bryan A. Thompson
Last Updated 2/9/03
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This box was designed to switch the load onto an alternate power input (when available) and to switch the load back to grid power when the alternate power is unavailable. The box also has a programmable time delay so that the load can be gradually added to the alternate power source.
Inputs and Outputs
Alternate Input - The alternate input cord is connected to the UPS outlet of the distribution box. When alternate power becomes available, the wall switch box waits the programmed time delay then directs the alternate power source to the output outlet. As long as the alternate power input is available, it is directed to the load connected to the output of the wall switch box.
Wall Input - The wall input cord is connected to grid power. When an alternate power source is unavailable, power for the output outlet is supplied by wall input cord.
Output Outlet - This is supplied by an alternate power source (if available), and from the grid in cases where the grid power is available and alternate power is not available.
Schematics and other notes
Important: Don't build this unless you know exactly what you're doing! I have nothing, so suing me for your stupidity wouldn't get you so much as a food stamp!
Everything is waterproof. I did this so that if I needed to use the Emergency Power Distribution System outside in the rain, I could.
Everything is rated for at least 20A. The relay is rated for 30A resistive load (or a 1.5HP electric motor) at 120VAC.
Everything is secured to the face plate of the waterproof enclosure so that it can be removed for easy maintenance.