I have this 5v/120v 10amp relay. How would I go about connecting it to a GFI type plug? Is it even possible with the common ground?
Assuming its not possible... Can I plug the incoming side into a GFI wall jack? or will it not like it?
I have never come across a GFI plug before but I did some googling and found it is the U.S. equivalent of what we call a RCD.
There is nothing particularly difficult about doing this but the fact you have to ask is telling me that you don't have the skill to do it correctly. I would strongly recommend that you get a local electrician to do the mains part for you. Also there is solder less breadboard in your photo. If you are dealing with mains you will have to have graduated beyond that stuff.
Make sure you wire-in your relay AFTER the GFI/RCD. That way there's fewer ways for you to electrocute yourself while you're debugging.
You haven't explained anything about what you want to do with the relay. The fact that there is a GFI/RCD is neither her nor there as to how you wire the relay. The relay coil is completely electrically isolated from the current being switched.
By convention the RCD/GFI of appliances with one integrated is located as close to the power source as possible, so as to protect the cable and switch as well as the appliance proper. I would recommend taking this approach as well.
Since this system im frankensteining together will be near water I want to be as safe as I can. The relay will be switching a water pump on and off.
GFI or GFCI is a ground fault interrupt that when it senses a lot of current it assumes that current is going through your body and into the ground. Not generally a good thing and blows its built in breaker. Possibly saving your ass.
Now when I wired up my bathroom during the remodel I remember there was something "different" about the way it was wired. And I remeber I kept popping the breaker on it until I rewired the ground.
Now since this relay uses a common ground for the in and out sides I wondered if there was a problem using a GFI with it.
@grumpy: bah electrician. I dont hire out, I learn from zapping myself. For this conversasion lets assume I'm not an idiot and I can keep the low and high voltage sides seperate in my hands and brain.
@RC hopefully less abstract now
@ gardner. You are saying just plug my In/source power into a real GFI? That is feasible I just wanted to verify that also wouldnt be a problem. Hence the second part of my question.
GFI or GFCI is a ground fault interrupt that when it senses a lot of current it assumes that current is going through your body and into the ground.
That is NOT how GFCI works! GFCI = Ground Fault Circuit Interrupter.
GFCI works by sensing a difference in current between the Hot and Neutral. The assumption is that when this occurs, there is a "fault" causing current to rush to "ground."
ok you explain better than I.. But the main point being when it senses something wrong it assumes you are dieing or a wire is melting and blows ;D
ok you explain better than I..
Better? No. I explained correctly. Your comment of "senses something wrong" is worrisome. You should understand WHAT it senses. You are dealing with something that is potentially lethal.
The last comment you made suggests you think a GFCI works like regular circuit breaker. It doesn't. It some cases a GFCI might trip if there is a short circuit, but that IS NOT what it is designed to detect. It detects current imbalances and is relatively slow compared to a typical circuit breaker.
Man you engineer types are rough around the edges. No vasaline or anything. :-*
Ok so I understaand better, and I assume I could google it. But for posterity reading this post...; By imbalance are you saying that normally the same amount of current that goes through the hot side should also be flowing out the ground side. And if there is an imbalance ie lots of hot and nothing coming back the ground, thats what causes it to trip?
Versus a Circut breaker that trips when more than Xamps or volts runs through it.
In a home's AC wiring, current flows through the Hot and Neutral. Neutral is NOT the same as Ground.
http://www.epanorama.net/documents/groundloop/why_grounding.html
No vasaline or anything
Same like the 120 volts that will course through your twitching corpse. No Vaseline whatsoever. You MUST get this right.
If you have to ask about any of this stuff here, you are not qualified to mess with it. Don't.
Far too many people do not understand the difference between neutral and ground, or what is meant when you tell them the electrical service to their home is 2-phase. Let's say it again! IF YOU DO NOT UNDERSTAND THE TERMS USED IN THESE POSTS ABOUT A.C. MAINS ELECTRICITY, CALL AN ELECTRICIAN!
Most people have been shocked at least once in their life by 120V.A.C. It hurts a little and you'll remember it! Add some water and a ground source, and you'll DIE!!!... Painfully!!!
DJ
If I was going to do such a thing (I am not an electrician) I would simply have the relay(triggered by the arduino 5V signal) controlling the HOT(?Black?) line prior to the GFCI. Then the Neutral (?White?) I would leave connected straight to the wall plug/circuit breaker etc. The GND (?green?) will also connect straight to the wall plug/circuit breaker.
DISCLAIMER: I am not an electrician. I offer no guarantee that this will not kill you. In fact I will tell you specifically to not try it. Do not try it, but if you do let us know. 
I feel so loved. Everybody wants to save me. How about if I wear Linemans gloves and rubber boots. then will you tell me? ok ok. I get the point. Ill go google it. I'm thinking Ill probably just plug the system into the GFCI thats already up there. Its just hard to get to.. For testing Ill take both wires and put them in a glass of water and see if it blows. ;D
An excellent example of what not to do.
Care to explain why?
i think this a is low voltage forum. I can understand why they dont want to help people blow themselves up. In fairness I fried a controller a few weeks ago by 1. not fully understanding the instructions I was given on this forum and 2. not connecting it properly even after I understood it. lol. fortunately they replaced the $300 controller under warrenty. Hard to get your left foot back under warrenty when it gets a big hole in it from grounding you out.
Recommending that someone do something.....is just an extremely questionable thing to do
I told him specifically to not do it.
Yes you shouldn't be touching your mains circuit if you are not qualified.
Can't we address this as an educational pursuit (In theory).
Other than that I do not see any technical reason why the setup I suggested wouldn't work.
check out
http://www.uchobby.com/index.php/2007/10/08/arduino-beer-thermostat/
"you'll shoot your eye out"