not robotics, but help would be appreciated

Technical Electrical
1

ok, i have a source of 115VAC(approx.) coming from the wall. it is currently going to a switch, then to lights that are in parallel, but the lights aren’t too important, i think. anyways, i was wondering if i could add 2 more light swtiches in parallel from the same source to the same set of lights without any complications.

i already know about saftey precautions, am using an appropriate guage wire, and wire nuts and what not…just wondering if i will have a potentially flammable problem with putting the switches in parallel, since putting them in series won’t work with what i have in mind…

thanks in advance

2

Could you draw a simple schematic (picture) of what exactly you want to do? It would help us be able to tell you if it will work/is safe/

3

…l 115VAC
…l
…l
…l
…┌–±----------┐
…l…l…l
…
…l…l…l
…l…l…l
…└—±---------┘
…l
…l this is going to the lights

please try to ignore the dots, and i hope this comes out ok
also, keep in mind, instead of another wire, the ends of the switches will go to a single wirenut that goes to the lights in the existing circut

4

So is the purpose of this to control the lights from three different places? It would seem to me that there is something in the NEC book about doing this. It is similar to the 2 switche layout (like one at each end of a hallway) but with 3 switches. However, if this is what you are doing, I believe that there need to be lines tied between the switches.

If I were you, I would head to your local Home Depot and pick up a copy of the NEC (National Electric Code) Book. It is green, costs either $19.99 or $29.99, and is in the electrical section.

I also may be describing something that is totally different from what you are looking to do. Am I on topic???

5

the problem with this schemtic is, that in order to turn the lights off you will need to turn off all three switches, but being that is the jist of the plan it should work, Because with a parallel circuit voltage is the same in each branch. So again this should work. I emphasise should, because what should work and what does work can be two different things.

6

If yoy run 1 common wire to each of the three switches then it will work. The only problem is that you must always turn off from the same switch. If you turn a 2nd switch on so that 2 are in the on position then you must make sure to turn both off.

Another way to do it is with a switch box that is connected to the three switches. A push on/push off button would work to trigger the switch box. I have heard about them but not sure where to purchase. Your 110V goes into the switch box and out to the lights, never to the switches.

7

drags out physics

OK, in parallel circuits, the total resistance actually decreases the more branches you add. (Weird, I know.) Ohm’s Law then tells us that if you decrease the resistance, you increase the current. Then, we also know that power=I2R. So the amount of power you’d be drawing would decrease because you’ve decreased the resitance, but then increase proportionally the the square of the corresponding increase in current.

In conclusion, I think I’ve totally confused myself. In terms of safety/starting fires/tripping breakers…it would depend on the specs of the circuit, unless I’m totally missing something (which I probably am, so feel free to correct me.)

8

That’s true, but the wires and switches offer such a small amount of resistance that it is considered to be of no importance. So the only real concern would be focused on the lights and since the circuit modifications are being done on the switches there won’t be any significant changes in power or current.

Laura Ohm’s law also states that in a parallel circuit, volatge is the same in all branches and V=I*R according to Ohm’s law also.

9

You are absoultly right. Parell branches resistivity can be calculated by taking the inverse sum of the inveresed branch resistivtys. Just keep hitting that 1/x key till you get the answer you expected, as my professor always said.

However, it’s not really an issue here. The resistence of each switch when closed is probably 1 or 2 ohms at most. So there is no real power savings putting three switches in there, since the total resistence with all 3 closed wouldn’t be much less then with one closed. For all intents and purposes. there is no real diffrence in the resistivity of the circuit, since far and away the major resistence there are the lightbulbs.

In terms of safety, assuming it is wired correctly, you won’t have any problems with fires or such. It is a little odd though.

10

If you are trying to turn off the lights from multiple locations than you want to use 3-way and 4-way switches. Your local home improvement center should have a book on wiring made easy, I use one from Sunset Publications.

All safety practices apply when working with electricity. Number one is to shut off power at the breaker, number two is to test the circuit to make sure you turned off the correct breaker! :eek:

11

i know about wiring and saftey things, been doing electrical for the team for 4 years…

and well. i think it should be fine, and as for having the lights off with all of them off, thats not a problem, and just turning on the one you want to make it work, it should be fine…

thanks everyone…

12

After talking with a some people about this you may want to try a circuit like this:

…115 Volts
…|
…Switch 1…o
…(spdt)…/
…o…o
…|…|
…Switch 2…o…o
…(DPST…\ /
…cross-…/./../
.switch)…o…o
…|…|
Switch 3…o…o
(spdt)…
…o
…|
…Lights

In this you use 2 single pole double throw switches and a double pole single throw switch. Agian try to ignore the dots.

13

I don’t think you have to worry about anything burning up with what you’re describing. But I’m very curious about what you have in mind!

Putting switches in parallel means that any single switch can turn the light on, but all switches have to be off before the light will turn off. If that’s what you want, great, though I’d still have to ask why that’s what you want. Never mind the implementation; can you give any more detail about the application?

14

The standard home center names for the switches are “two way”, “Three way” and “four way” switches. Two way switches are used when only one switch will control the device, three ways are used in pairs and four ways are used between three ways to get more than two switches in a circuit. You should be able to find all three types at you local home center. The four way are typically more pricey because they are less common. The circuit above has two three way switches and one four way switch. For the three way make sure you identify the “common” terminal when wiring. On the four way you need to identify the pairs (look for a diagram on the box or the switch back).

Hope this helps!

Good LucK!

15

actually, what i have in mind for is far less interesting than the most lame of any of your dreams…

well, the lights that go to the washer and dryer in the basement are on my aunts side of the basement. for convenience, she has them right at the top of the stairs, so me coming in from the other side is a pain, that and when i turn the lights off, i have to count how many steps i took up, count that many down, and watch my head because i am kind of tall, and the shelf on the stairs is low…

also, if i want to come in from the bulkhead, i need to do the stair thing, so i am putting in additional switches for my stairs heading down, and the bulkhead, along with the other original switch, so thats the 3 switches in parallel, with an explanation…

oh, and a side note im out of school…if only i was happy about it…and thanks for everyones advice, was pretty sure about it not starting a fire, just wanted to check…

edit:

I don’t think you have to worry about anything burning up with what you’re describing. But I’m very curious about what you have in mind!

Putting switches in parallel means that any single switch can turn the light on, but all switches have to be off before the light will turn off. If that’s what you want, great, though I’d still have to ask why that’s what you want. Never mind the implementation; can you give any more detail about the application?

well, what i am doing is the first thing everyone does when playing with a new form of electricity, lightbulbs of course…

16

Actually, all the stuff about increasing yet decreasing could be explained a lot clearer and in an easy-to-understand way. :slight_smile:

Given V=IR and P=I2R; we know that IR is always constant because your voltage will remain constant, so IR can equal K. Essentially P=I(IR) *, so P=KI. This shows that you need not worry about decreasing resistance, compensating in amperage, and increasing due to squaring; rather, there’s just a simple linear relationship.

You could even graph it if you wanted to, whereas P=y, K=m, and I=x under the function y=mx+b! (b=0, obviously, because when your voltage is zero your IR HAS to be zero as well)*

17

there is another way you can do this without having to run romex (power) wires

there is a low voltage control system for 120VAC applications - bascially you put this small relay module inside the light fixture, and it only takes a pulse of 12VAC to switch it on or off

so you can put the control switches anywhere in your house, and have as many as you want controlling one light or outlet -and you only need to run doorbell wire for the controls intsead of 3 conductor 14 gauge romex.

Its pretty neat - if you wire your whole house this way (when its built preferrably) you can also have a master control box, like in your bedroom, and if you want to hold the ‘on’ button down and sweep the selector switch - and turn all the lights on in your house in about a second

or turn them all off :^)

18

What about the ‘network’ setup that uses regular wiring? it sends a bit when the AC current hits zero (sine-wave thing). So in the USA, that’s 60 bps. I can’t remember what it’s called!

(and for anyone using dots to draw, try the

 tag)
19

You could also use X-10. There are lamp and appliance modules that each have switches to assign a unique House and Item number. You just plug it into a wall outlet and then plug the lamp into it. They have various RF remotes that you can program to actuate the different modules. It requires no wiring at all, but houses on the same transformer will share signals.

The remotes work with a receiver that plugs into a wall outlet to send the X-10 commands to the units over the home wiring. There is also a computer module so you can send X-10 commands from a PC. The basic stamp also has X-10 capability built in. They also have some nifty motion sensors so you could turn the lights on when you start walking down the stairs.

20

Operating a light from two or more switches is very common situation and has been done in house wiring for many, many years. The proper way to do it without going to a low voltage system is as GeneF describes.

From you comments, I strongly advise you hire or enlist the aid of an electrician who is familiar with the wiring codes in your area.

Mr. Bill