How to wire a relay?

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  #1  
Old 09-03-11, 08:37 PM
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How to wire a relay?

Not familiar with the wiring schematic below. With a relay the coil gets energized by the load you want to initiate the switching with and the thrown poles will be the ones with the other circuit that you want to act in synch with the first. So how would you wire this relay? I assume that we are switching hot.

 
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  #2  
Old 09-03-11, 09:34 PM
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What is the purpose of this set up.
 
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Old 09-03-11, 11:54 PM
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13/A1 and 14/A2 are the coil leads, they will connect to the source power and the pilot device in series.

1/12 is the normally closed contact of the relay. 5/14 is the normally open contact of the relay and 9/11 is the armature of the relay. 1/12 closes to 9/11 when the coil is NOT energized and 5/14 closes to 9/11 when the coil IS energized.
 
  #4  
Old 09-04-11, 07:06 AM
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Ray, the relay is for 120v ac for holiday outdoor lighting via receptacle. I have a switched recept. (circuit 1) that I would like to use to trigger another circuit (circuit 2) so that I don't overload the first circuit.

Furd, the item I want to use is a spdt relay. I drew up what I thought might be the correct wiring, but I am not sure. It seem that circuit 1 would energize the coil and close the contact between 9 (common) and 5/1 (since its double pole).

Does egc play a role in any of this or just neutral and line?

Thanks in advance.
 
  #5  
Old 09-04-11, 09:00 AM
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Ray, the relay is for 120v ac for holiday outdoor lighting via receptacle. I have a switched recept. (circuit 1) that I would like to use to trigger another circuit (circuit 2) so that I don't overload the first circuit.
How many and of what types of lights do you plan on using? This may be completely unnecessary.
Does egc play a role in any of this or just neutral and line?
No. It just goes to the enclosure.


What type of enclosure do you plan on mounting this in, and is it hardwired or portable?
 
  #6  
Old 09-04-11, 11:11 AM
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Justin, here is an excerpt from an old thread:

Triggered load switching

I have a home lighting system and one of the switches is used to power outdoor lights for Christmas displays, etc. The switch is not rated for more than about 10 amps and last year the device was hot while in use. I clamped the exterior loads and sure enough it was at about 9A.

What I would like to do is add a box with two duplex outlets run on a separate 15A circuit but still have it triggered when this old switch is turned on.

Is it possible to use a relay? What do I look for?
(I'm thinking when the relay senses 120v at the old receps it triggers to allow 120v to flow at the new receps off of the new circuit??)

Thanks in advance.


The enclosure is a deep 4 square.
 
  #7  
Old 09-04-11, 11:28 AM
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Why not just use a single two pole relay with a 120v coil? Each plug-in on the receptacle would be supplied by a separate circuit with the hot of each going to one pole of the relay. The switch would control the relay. If the switched power was used for one circuit only a single one pole relay would be needed.
 
  #8  
Old 09-04-11, 12:07 PM
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Thanks for the other suggestions, but at this point I have the product on order it is a magnacraft 781XAXC-120A with 5 pins as pictured below in first post. I just want to make sure I correctly hook it up. I believe I have incorrectly drawn the diagram in the previous post. Here's the updated one:


When circuit 1 is switched on from light switch in house, current passes through the coil energizing it, causing switched legs 5 & 9 to complete circuit. I assume the one pole that is unused can be left empty - might come in handy if I need to go to the other side of the house.
 

Last edited by chopnhack; 09-04-11 at 12:34 PM.
  #9  
Old 09-04-11, 05:41 PM
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Your diagram looks good to go! Your receptacles will need gfi protection with bubble covers, and the 4x4 box will need to be in a dry location.
 
  #10  
Old 09-05-11, 05:25 AM
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Just so you're sure:
Circuit #1 has hot & neutral on the relay coil, but only the hot is switched at the triggering source.
Circuit #2 is a switch leg (hot only), but the load still needs a neutral at the recep.

You won't be able to use pin 1 for the other side of the house. Pins 1 and 5 are mutually exclusive. Coil energized = Pin 5 hot. Coil de-energized = Pin 1 hot.

In fact, it's a good idea to protect pin 1 from accidental touches. Hopefully you bought the socket for the relay. It results in a safer and more professional installation.

Most people who do this for holiday lighting use Solid State Relays. SSR's are easier to wire and have no mechanical parts to fail.
 
  #11  
Old 09-05-11, 06:59 AM
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Thanks Justin! Everything else is in place already.

Awesome input Rick, yes on circuit #1, I left it out on circuit #2 for clarity, but yes there is egc and neutral in that recep.

"Pins 1 and 5 are mutually exclusive. " I don't understand. I thought it was a spdt which meant that the two throws equals two terminals that are switched together. Its not an issue as I can pigtail the one terminal for the two sides of the house. By the line drawing I thought pin 1 and 5 were electrically tied?

I did buy the socket as well as the hold down spring I didnt want this to accidentally ground out inside the metal 4 square thats in the garage.

I had seen the ss relays before but they were too expensive for this application. The mechanical life on the relay was rated at 100's of thousands of powered switches which in our case will be many lifetimes

Thanks for all the input.
 
  #12  
Old 09-06-11, 05:10 AM
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There are two outputs on a SPDT relay: Normally Closed (NC) and Normally Open (NO).

As Furd said, Pin 1 is the NC contact of the relay and Pin 5 is the NO. When the coil is not energized these are the "normal" states of the outputs. They reverse when the coil is energized.

Energizing the coil makes it a magnet that attracts the wiper (Pin 9), causing it to stop contacting Pin 1 and make contact with Pin 5. You can see this happen on a mechanical relay by watching it when you energize the coil.
 
  #13  
Old 09-07-11, 12:00 PM
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The schematic is not clear to that effect Rick, so what I will do is when I get the relay I will check for continuity with DVM to find the NC and NO outputs to make sure I wire it correctly. Thanks for the info and clarifications. :-)
 
  #14  
Old 09-08-11, 03:35 AM
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Actually the schematic does show the connections. The angled line to the right of pin 5 represents the swing of the armature when the coil is not energized ("normal"). It is in contact with the connection to pin 1. The open space between the angled line and pin 5 shows that connection to be open.

Still, it's smart to verify your wiring with a meter.
 
  #15  
Old 09-08-11, 09:26 AM
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Thanks Rick! I didn't notice the tiny gap between pin 5 and the armature before, thanks for clearing that up.
 
  #16  
Old 09-09-11, 01:57 PM
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For future reference, a "relay-in-a-box" from a company like Functional Devices would have been a good choice for this project.
 
  #17  
Old 09-10-11, 10:29 PM
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That would have been nice, but a quick glance shows ~$65 whereas what I used was $10.
 
  #18  
Old 09-11-11, 05:44 AM
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Originally Posted by chopnhack View Post
That would have been nice, but a quick glance shows ~$65 whereas what I used was $10.
A SPDT 20A relay-in-a-box can be purchased online for $17+S&H. A SPST 20A relay-in-a-box with an override switch can be purchased online for $22+S&H. Both have built-in transient protection, coil power LED indicator, and variable coil voltages.
 
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Old 09-11-11, 06:54 AM
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That's way better, do you have a link? I already have the part, but it would be good to look at and keep in mind for any future projects. Thanks!
 
  #20  
Old 09-11-11, 07:03 AM
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Best thing to do is go to the Functional Devices website and find the part number for the relay you want. Then google the part number (maybe add the word "relay" or "Functional Devices" to narrow the search). I've bought them from energyequipment.com and hvacusa.com.
 
  #21  
Old 09-12-11, 03:42 PM
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Maybe I got it wrong.... when I wired up per the schematic below it tripped my GFCI outlet which was the source. Thankfully it was there. I believe that having the line and neutral across the coil is creating a dead short. Am I wrong here? Was the proper way to wire this to take the line from the source, put that on one side of the coil and then return the line exiting the other terminal of the coil to the source?
 
  #22  
Old 09-13-11, 07:13 AM
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I am stumped... can anyone lend a hand?
 
  #23  
Old 09-13-11, 08:00 AM
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Your diagram in post #8, along with the followup comments from Rick, is correct. If you have it wired that way, my guess is that you have a bad relay, a bad socket, or you when you mounted the socket/relay in the box, you made contact between one of the wires/terminals and the box. Maybe you have a short in the wiring. If it were me, I would diagnose it piece by piece. Take the relay/socket out of the box. Disconnect all the wires from it. Make sure the nueutral and hot from circuit one are capped off and not touching anything. Throw the switch on circuit one to see if the GFCI trips. If it doesn't, turn off circuit one, connect the circuit one hot and neutral to the coil, turn on circuit one and see if it trips. If it doesn't, turn off circuit one, connect the circuit two wires and try again. If it still doesn't trip, put everything back in the box and try again. This process is basically trying to isolate exactly where the failure occurs. When you know that, you should be able to fix it.
 
  #24  
Old 09-13-11, 11:28 AM
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Thanks ibroussard. The one thing that I did immediately as far as diagnosis goes was to pull the relay and test the coil. It had 4.2k ohms, so the coil is good according to specs. Are you sure that the coil gets hot and neutral across it? Aren't we just creating a dead short across the coil? I was thinking this is why the GFCI tripped. I will take each piece apart a little later on, thanks for the advice.

Going back to what Furd said in post #3, he mentions putting the two leads to the coil in series with the power supply and the pilot device.... That confuses me because I need to power the pilot device with the separate power from the new circuit.
 

Last edited by chopnhack; 09-13-11 at 11:43 AM.
  #25  
Old 09-13-11, 12:10 PM
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I'm not sure what Furd was saying in post #3, but then again, I'm not a professional electrician.

A relay coil is like any other electrical/electronic device. It needs both hot and neutral (if Vac) or positive and negative (if Vdc) to operate. It is really just an electromagnet. If you are saying that the coil is bad because it has 4.2k ohms across it instead of being completely open, I doubt that is correct. It may be that the coil actually needs a lower voltage to operate, and it has a 4.2k ohm (or similar) resistor in series to drop the voltage. If you think you are creating a dead short just by hooking up the hot and neutral to the two terminals, try this...unplug a small electrical appliance like a can opener. Check the resistance across the electrical plug terminals on the can opener's power cord. It's probably an open circuit. Do whatever action it normally takes to turn on the can opener (but leave it unplugged), and test the resistance again. With it "on", it will probably have a very low resistance.
 
  #26  
Old 09-13-11, 02:37 PM
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The coil is not causing a short. At 4.2k ohms it's drawing milliamps. Measure the resistance of a standard 100-watt light bulb and you'll see about 10 ohms. (Which increases to nearly 150 when it's heated.) The coil, just like a light bulb, is an electrical "load" that requires a hot and neutral.

In addition to ibroussard's excellent troubleshooting suggestions ... Suspect the GFCI. It may be doing its job by sensing the momentary current differential as the relay coil becomes energized. (It is, after all, an inductor. GFCI's sometimes have issues with inductive loads.)

Make absolutely sure that your wiring to the coil is correct: one side hot, the other side neutral. Disconnect everything else from the relay. Plug it into a non-GFCI-protected outlet. You should hear the relay click. If it does, connect everything else and test. The GFCI is the problem.
 
  #27  
Old 09-13-11, 05:32 PM
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I got it working! You guys are both awesome, let me explain what happened, I was wrapping up the wiring a few days ago while entertaining the 2 and 4 year old boys and I forgot what set of wires was which (and yes the lines were not energized and no they were not let near the area nor was I touching the wires with my hands)

I didn't imagine that the wiring was wrong and started to wonder if I really understood the basics of a relay properly! I pigtailed off of the line before the GFCI to avoid what you mentioned Rick. So I had my input wired to the normally open side of the relay and vice versa. Everything works as it should now, I appreciate everyone's input and patience. :-)
 
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