Relay controlled outlet box

Other Hardware General Electronics
1

I've seen a few different setups for building an outlet box and was a little curious.

I have seen both normal cheap outlets used and GFCI. I was thinking maybe GFCI was a good idea but then i came across two issues

  1. cant split the outlet (each plug controlled by a relay)
  2. most GFCI are 15-20amp, most relay (kits) i've seen are 10 amp (obviously there are some out there, but cost/size wise im not sure it makes sense to bother with)

so it seems like unless i get an expensive relay the GFCI isnt likely to protect anything

Then I was thinking i could toss a 'blank' GFCI in front of the relay, which if something went wrong would toast the relay but anything else would be fine. however, i assume that 'anything else' is really nothing more than where i'd reset the breaker? (my box vs the house panel)

So it kinda seems like i should just go really basic (10amp relay with cheap outlets to split) and not worry about it?

Obviously i'd just make sure nothing i tossed on any particular outlet was more than 10 amp

2

Wowow, stop!

First, a GFCI does NOT protect you from over current/shorts. Just from a Ground Fault after which the Circuit is [/b]Interrupted.

As for the current rating on those that's the max current of the circuit that's part of. But you need a fuse or a breaker to break the circuit in case of over current. Aka, a 20A GFCI is suitable for a circuit which is protected by 20A breaker or less (and the cabling can withstand the breaker rating).

If you want to use a 10A relay, that's fine. But you have to include something to break if the current exceeds 10A (if it's not on a 10A breaker). Because a component is the circuit (like the wiring or a relay!) may never be the safety!

And about 1), huh??? You can have multiple outlets behind a single GFCI. In Europe it's even common to have a GFCI in the breaker box (on every breaker).

But 10A is a lot and mains is dangerous... (Shock and fire) And if you're asking this I don't think you're ready for the task...

3

Sorry, I don't understand your project at all!

You can control an outlet with a relay. There are just a couple of issues to be aware of -

The Arduino can't directly-drive a relay coil, so you either have to make a simple transistor/MOSFET driver circuit, or you can buy relay boards with the driver built-in.

The relay coil generally needs it's own separate power supply (or you should have separate voltage regulators for the Arduino and relay). Or, if you use a 12V coil and a 12V power supply the Arduino's on-board 5V regulator may provide enough "isolation" to prevent glitches when the relay switches.

There isn't usually enough room inside the electrical box to put the relay inside. If you want to control a single-outlet, a double-outlet box gives you extra space (and you can get an outlet-cover with on side blank). I have made some small "homemade" solid state relays with an opto-isolator and TRIAC, and jammed 4 of them into a quad outlet box, but it's a mess!

And it might be illegal (a building code violation) to mix low-voltage and line voltage in an electrical box that's part of a structure.

You can get solid state relays that CAN be directly driven by the 5V low-current output from an Arduino. These are super-easy to use and if you get the [u]industrial type[/u] with screw terminals, they are super-easy to wire up.

Depending on your project you might look-into some [u]home automation[/u] products. You can buy wirelessly-controlled outlets (and switches/dimmers) that fit-into a standard outlet box.

I don't get what GFCI has to do with this, unless you want to "hack" it to use the internal relay? That doesn't seem like a "smart" thing to do...

GFCI has a particular purpose... It senses current through ground and cut-off power. So if you are drying your hair while taking a bath and drop the hair dryer in the water, it shuts-off power when it senses current though water to ground, hopefully in time for your heart to re-start.

I've been told that you can wire multiple outlets to the GFCI so all of the following outlets down the string are also protected. That makes sense... One GFCI outlet can protect the whole kitchen or the whole bathroom.

4

@septillion

A 'Split Outlet' is where each plug on the outlet (2) are separately powered. By default they are both powered by by the same line. The cheaper outlets have a "tab" that you can pull out that split the two. The GFCI doesnt have the "tab" for removal (for good reason). I believe normally there are "in" and "out" screws so you can chain them. If you remove the tab each set of screws is an "in" for each plug, commonly used to make a lamp work with a wall switch.

So basically without the "split" both plugs would be controlled via a single relay switch (would rather have each plug controlled)

I guess I should also add im not looking to power any of my creations, im trying to get my creation to control the power of a device. So although you are spot on that im a bit lost, im not as worried since its unlikely any of those devices will cause an issue, I need to switch a lamp and a small pump on/off based on sensor input.

@DVDdoug

Im currently using a relay board for the reasons you stated, the 4 relay board fits perfectly in a 2 gang outlet box. Ideally i'd like to get the two outlets (4 plugs) each on a relay so that i can control all 4.

I did look for pre-built products and found a couple but most had far more features ($$) than i was looking for or had no way to control the NO/NC state of things (like 2 NC / 2 NO). If you've found a product with a tad more control but not as nutty as wifi please share a link! Im thinking the X10 might be a pain since I dont have any X10 but I do have zwave, however those are $30+ per outlet, not split, and then would require my zwave control to always be available (pesky Smartthings)

Also your comment about chaining outlets to a single GFCI is correct and was REALLY infuriating when it tripped in my house. They chained the two upstairs bathrooms together with a single GFCI in the main bathroom (never use it really) and then chained on to the master, so when that managed to trip it took a REAL long time to figure out the two were linked and the GFCI was actually in the main bathroom :-/

Thanks!

5

If your creation is the end device or the device in the middle makes NO difference. Still mains going through YOUR creation.

And ah, would have been a good idea to post images o at least mention you're in America. But then again, most Americans forget the rest of the world exists... But you only need a single GFCI for a whole bunch of outlets. With a GFCI outlet you can indeed use the out/link terminal. But remember, a GFCI does NOT protect your circuit whatsoever. It's meant to protect you (in case of a Ground Fault).

What you DO need in series with you're switched outed is a fuse/breaker with a max rating of that of the weakest component. That being the cable or the relay.

The Solid State relay DVDdoug posted is rated for 40A (if you get a genuine one). But only with a very large heat sink! Fine to switch a couple of amps without heat sink but again, add a fuse/breaker to protect everything!

Another nice solid state relay is the G3MB-202P. Not as powerful but nice and small. Again, add a fuse/breaker!

As a ready made solution the a SonOff is a nice solution. There is custom firmware available for them so you can do anything with them. And the Wifi, yeah, I'm not a fan of that for outlets as well. But for you it's a easy, cheap and especially safe solution.

And yeah, linking a GFCI to another room is a bit weird. We (Europeans) have them in the breaker box. Multiple rooms can share a single GFCI but at least they are in a single place so you can spot the tripped GFCI/breaker right away.

6

And in my neck of the woods, GFCIs in the breaker box are overload switches - combined functionality.

7

As if it's not annoying enough the damn thing has multiple names, some like to see the world burn and use the same name for multiple devices... Not blaming you Paul, know it's common in some places, but it's pretty damn annoying. At least the British have two names for them, RCD and RCBO.

PS I hate most RCBO's because most of them don't have an indicator what tripped it, over current or a ground fault... Glad they are rare around here.

8

septillion:
As if it's not annoying enough the damn thing has multiple names, some like to see the world burn and use the same name for multiple devices... Not blaming you Paul, know it's common in some places, but it's pretty damn annoying. At least the British have two names for them, RCD and RCBO.

PS I hate most RCBO's because most of them don't have an indicator what tripped it, over current or a ground fault... Glad they are rare around here.

True.
However they take less space in the DB compared to having to install both RCD+MCB . In mains outlet ring circuits RCD is a must with the latest regulations.

9

Here a RCD is a must, done* :stuck_out_tongue: And the concept of a RCBO is fine and I like them IF they have some kind of indicator to identify between GF en OC. But the cheapies tend to not have that. :confused:

*for domestic use.

10

Hi,
Can you help clarify this;

A 'Split Outlet' is where each plug on the outlet (2) are separately powered.

to;
A 'Dual Outlet' is where each of the two sockets on the outlet are separately switched.
gpo.png

Tom... :slight_smile: