I removed an electrical outlet by simply disconnecting three wires (ground, hot, and common) and isolating the end of each wire with electrical tape. I have covered the hole and finished the paint work. Now I noticed that a few switches and outlets on another floor of the house stopped working (my non contact voltage detector shows outlets are hot, but connected devices don't work). How can I tell if what I did caused the problem?
You disconnected wires that were hot, wrapped them with electrical tape, and buried them in the wall after removing the junction box. You're not allowed to do that.
You can't terminate live wires anywhere but a box.
So you have 3 choices.
- Follow the cable to wherever it goes, positively identify that it that same cable, and remove it from there also, pulling the entire cable out of the wall (or at least, as much as it's possible to remove). That permanently removes the cable from service.
- Route the cable to a place where you can put a junction box, bring them into the box nice-n-legal with appropriate cable clamps, secure them, and then put a blank junction box cover on it. Or a recep if you want.
- Use a Tyco style in-wall splice to extend the cable to somewhere you actually do want a receptacle, fit a box there, and fit a recep there. This may help with the next part.
Every point on a wall must be within 6' of a recep
(that means following the wall and rounding corners, but not crossing thresholds; presuming the person will lay the appliance cord along the wall perimeter. Standard cords are 6' long). So what can happen when you remove a recep higgledy-piggledy, is now you leave a significant part of your wall inaccessible to any receptacle. That's a code violation.
It is even a code violation if your site is grandfathered to before that was a requirement: you're not allowed to make things worse.
As far as the other circuits breaking
I think there's more to this story. I think there were more wires than the ones you have mentioned.
If you removed only ONE wire of each color from the receptacle, then it should not have been an issue. But if you removed TWO wires of the same color, they should have been reconnected with a wire nut, otherwise you broke the continuity of the circuit. Sounds like you may have done that with the common (neutral) wire.
If you also just closed up the hole with a patch and painted over it, that was illegal. Once there is a box that has connections in it, you are required to provide access to that box to periodically check the connections. You can put a blank cover plate on it, but you cannot bury the box and connections into the wall and hide it.