That's it for parts.

I'm sure you can find a cheaper relay, this one is a 10 amp DPDT and should be good enough for just about any appliance. All you need is a SPST 120v relay which should be cheaper. Just make sure it can handle the current you plan on drawing.

Cut off the receptacle end of the 2 wire extension cord and discard the end.

Assemble everything inside the outlet box. Apply heat shrink tubing or electrical tape to all connections.

Connect (solder) the wires of the ext cord to the relay coil (pins 7 and 8)

Connect the green/ground wire of the power cord to the ground lug on the duplex outlet

Connect the white wire of the power cord to the silver terminal of the duplex outlet.

Connect (solder) the black wire from the power cord to pin 3 of the relay.

Connect (solder) a black jumper wire from pin 4 of the relay to the brass screw terminal of the duplex outlet.

It will all fit into the box. The relay will fit if laid on its side at one end of the box with the longer side of the relay parallel to the short side of the box.

Insert the control cable and the power cord through the strain relief. I used two but inserting both wires into one will work just as well.

Plug the control cord into an outlet on your DC8/4
Plug the power cord into a power source
Plug the appliance into the duplex outlet.

When the DC8/4 outlet is activated it will energize the relay and close pins 3 and 5 completing the circuit and applying power to the appliance.

I ran the control cord through my floor to the room below where my chiller sits and use the DC8, remoted with this expansion outlet, to control the chiller.

Yes, AC expansion outlet

Here's a quick and dirty diagram.  Blue is the outlet box, red is relay and sits under duplex outlet at one end of the box and the rest should be self explanitory

for those of us slower uhh...less techincal people, this is to expand the amount of items you have pluged into a DC8/4?  Do you have any pictures? 

This is a DIY version of Neptune's Expanshion Outlet.  It allows you to either expand or remote a DC4/8 outlet (does not add more uniquely addressible outlets)  It also lets you plug a high current draw item into a DC4/8 without adding much to the current limit of the DC4/8 because items plugged into this expansion outlet, while controlled by the outlet in the DCx that it's control line is plugged into, is powered by a separate plug/source.

And sorry, no pics but the diagram has all the parts..

ahhh I see, so its another version of this?

http://www.aquariumcontrollers.com/...tender.php

Yea, same functionality as far as I can tell.

ok thanks!