3 Way Versus a Relay?


Old 10-14-04, 09:41 AM
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3 Way Versus a Relay?

I have multiple spotlights around the house that I turn on & off at various times. All were wired by me a few years back and feed from the basement to individual single pole light switches. The JB's where the switches and feeds are spliced are in the basement so are still completely accessable.

I am in the process of installing an alarm system in the house. It's a pretty good control unit with LCD Touchscreen Keypads that can also control lights via X-10 (which I never trusted) or by triggering 12VDC relays. The panel I believe can handle up to 16 individual relays. I intend to use one per light

The key to this is that they can be programmed to trip via an input from the keypad or automatically turn on in the event of an alarm condition at night which is what I really want.

The small low voltage relays are not rated to handle the lighting loads, so I intend to have them trip larger DPDT 120VAC 10 Amp rated Relays which I can get at work and will put in a separate can next to the Alarm Panel. That way there is no mixing of low and high volatge in any box.

My question is, do I have to wire the relays in to the existing lighting circuits like you would a 3-way? From a circuit standpoint it would seem to be easier to just parallel the power at the JB. In other words, it wouldn't matter if the switch was on or off, power would still get to the light via the pole on the 120VAC relay. More importantly, no one (like a burglar) could shut the outdoor lights off just by flicking a switch during an alarm condition.

I am concerned about code and safety issues. I do realize that someone could be working on that light someday (after I'm dead and gone) thinking the switch was off and then the alarm comes along, trips and puts juice on the leg....bad day, they would certainly curse the memory of me.

Has anyone mixed standard light switches and automatic controls on a residential light circuit before and what is the preferred and correct method. I think I gave as many details as I can think of.

Thanks in advance for any help.

paul o's
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Old 10-14-04, 10:10 AM
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Location: Central New York State
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Nobody should ever be working on a circuit by turning off a switch. The only safe way to work on a circuit is to remove the fuse(s) or turn off the breaker(s). Doing so is a sign of stupidity, or ignorance, or both, and means the person should not be doing electrical work in the first place.

There is nothing wrong with wiring lights or receptacles to be controlled by parallel switches. This is done more than you might think.

However, you should not be building something yourself. You should be using off the shelf UL (or similar) approved devices. Building something yourself is asking for trouble, and is likely not to be allowed by your local codes.
Old 10-14-04, 03:05 PM
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Ok, but I'm lost on the "building something yourself".

The alarm documentation states that the relays can be used to control various devices including lights. But I realized quickly that the contacts of the addressable relays are only rated for something like 500 mils at 12VDC. Enough basically to trip the coil of a properly rated relay.

If I were to use a U.L. Electrically rated can with a proper cover, say 18"x18" and mount (6) 120VAC 10 Amp relays on a DIN rail, grounded everything properly and used correct terminations, wouldn't that be considered a proper assembly and within code if ever inspected?

When I do electrical in the house it's clean and neat, but some things seem to need assembly.

Do you feel this aspect of the project shouldn't be done by me or not done at all? I was an Alarm installer and Field Technician for quite a few years. But if your advice is to bring in a licensed guy for the electrical to be safe, I will heed your advice.

By the way, this is a great forum, the advice here is top notch.

Thanks in advance
paul o's
Old 10-14-04, 03:26 PM
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What I meant by building something yourself was taking components from here there or anywhere and wiring them together, without due regard for good workmanship, or safe practices.

You would not believe some of the things that people come up with. I have seen lamp cord (18 guage flexible wire) run in walls. I have seen 18 guage extension cords running computers. We hear about people connecting ground terminals to the neutral line. The list of homemade fixes and wiring goes on and on.

You do sound like you are wary of the ratings of the various relays, and that you want a safe installation. If you feel that you can make something safely then go for it. But you may also want to look around. What you want is probably available commercially, and perhaps even for less cost.
Old 10-14-04, 03:43 PM
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Ok, I gotcha now Bob.

As a Systems Integrator I am so used to "assembling" systems for people that I forgot that something "commercial" probably exists.

I will hit the web and see if I can find a "premade" multi circuit control box with the proper ratings. One of those Home Automation sites might have something.

Thanks Bob, maybe I was thinking too hard. And I promise this weekend to yank all the "zipcord" out of my walls.

Have a great night
paul o's
Old 10-14-04, 03:58 PM
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I regularly assemble my own relay enclosures using off the shelf boxes but their use is solely at the discretion of our local inspector.
Here, the guidelines I follow are to use only approved relays, switches and connectors, to make sure that there is no crowding and that everything is super neat.
Our code also allows the mixing of low and high voltage wiring in the same conduit or box as long as the low voltage wire is rated for the highest voltage in the box.

As far as the circuitry, if you have the switches wired to a junction box, paralleling the relay contacts with the switch would be the thing to do.
Old 10-15-04, 01:37 AM
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Hi guys just was reading this post so far, it sounds interesting what you plan to do with the alarm system.
Just one question i would like to understand more is when you say like wire the relay parallel to the switch, how would this connection look, i think i understand what you are saying but would like to just confirm. I take you just wire to the same terminals and when the alarm trips the 12Vdc relay that fires the 10A Relay to complete the lighting circuit thats right isnt it.
Sorry to be a nusience, just interested in learning haha.

Old 10-15-04, 09:34 AM
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Right now in the basement, I have a 4" Square box with (3) Romex's coming in to it. (1) goes to the outside light, (1) comes from the switch, (1) is incoming 120VAC power. To make things simple, forget about the grounds for now. I connect the white from the power to the white to the light. I connect the black from the power to the black of the switch. When the switched is turned on it will allow power to come back down the white (I put a piece of black tape on the white to show that it is really black or hot now).

That white with the black tape is spliced to the black going to the light. A complete circuit.

Now to add a parallel relay in to the circuit. I would run another romex to the new relay box. Back at the 4" Square box, I would splice my new black from the new Romex to the Romex that was incoming power Black to Black. I would then mark the new white with Black tape and add it to the existing splice where the black from the light is.

At the relay (which is really just an automatic switch) I would put the black and the white of my new Romex on the two terminal screws of contacts of the realy.

In english, what we have done here is to parallel or side by side the two circuits. If you flick the light switch power runs down the wire and out to the light.

But if the switch is off and the Alarm System trips the relay. The contacts in the relay close (just like the light switch) and let power go out to the light also. This way it doesn't matter if the light switch is on or off, the light still turns on. And if the switch was on and the relay was on, that wouldn't matter either because both are routing the power from the same source.

If you would like a little diagram, I could email a sketch. When you look at it, you'll see it's pretty easy. The thing to remember for a beginner is that when you are using Romex, you always have a black and a white in each cable. When you start doing multiple circuits, splices and lights you may have many whites that you are using not as a neutral but as a return wire to carry power back from a switch. Hence the piece of black tape to REMIND you that this wire is now hot and not neutral.

Many times I have looked at a junction box and have seen 4 5 or 6 whites and I know some are actually hot. I spend extra time to make sure I know what each one does. A black and a White spliced to together are bad.

I didn't mean to "over explain", but if done properly, working with circuits is interesting and a great feeling when you flick that switch or fire that relay and everything turns on and works as planned.

Best of luck
paul o's
Old 10-15-04, 09:45 AM
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I re-read your post and I think I way over explained the situation (and probably bored the hell out of you).

Yes you are right.

Basically power comes in to the box and goes to the switch and the relay at the same time. Whichever one closes...the light turns on.

Sorry, I spent way too many years teaching apprentices. Sometimes I go too far.

Old 10-15-04, 12:28 PM
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Thanks Paul_OS i enjoyed reading the post im very much into electronice and just want to learn as much as i can, i hope when i get to canada that i can get an apprenticeship with someone who knows as much as you and explains it in a way i can understand.

Thanks for taking the time to reply.

Old 10-15-04, 12:31 PM
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By the way Paul_OS im nearly a qualified Electrician in Uk, but i like to explore the world of electronics do you know any good sites with Alarms etc im trrying to get some info on them.

thanks for your reply though i havnt thought about using relays before.

thanks again

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