ECN Forum Forums General Topics of the Trade General Discussion Area Lighting a tunnel?

We seem to keep hinting at this, and then saying 'you shouldn't know about this because you shouldn't use it.'

My opinion is that every electrician should know about wrong ways of doing things, and why they are wrong, so that they can recognize and correct the problems. With this in mind, strokezilla, I'd suggest that you look up the 'french three way' circuit. The same circuit goes by lots of different slang names. It is a three way circuit that requires switching the neutral, and it is a big no-no, for a number of safety reasons.

Once you understand how a french three way works, then you will be able to 'generalize' it to your problem, and come up with an 'illegal' answer that would function as your instructor described; 6 switches, 6 lights, flip a switch and one ahead turns on and one behind turns off.

Personally I would rather set it up with seven switches and a way to turn all the lights off.

Finally, if you are allowed to use double pole double throw switches, then you could make this system work as described, and you could make it legal. I think that the illegal approach is more 'interesting' as theory, but not what you should install.

For extra extra credit, analyze exactly what is wrong with the 'french three way', and all the ways that it violates code, and find a 'work around' that uses the essential circuit concept but makes it code legal. (I don't even know if this is possible, but I have a few guesses.)

-Jon

I can do it with 6 swicthes, 6 lights, if you throw in a plc.


Dnk......

I may not have the specified problem quite right, but if what is desired is to have at the beginning of the tunnel/hall is a switch and a light overhead, then another switch say halfway to the next light, and so on down the tunnel, then:

first switch (SPST) switches the feed from the panel and powers up the entire system (presumidly the subsequent switches were left to power light bulb #1 by the last person who came back thru the tunnel) and light bulb #1 (fed on the hot side thru a SPDT (3 way)). The hot wire from the first switch feeds the center of this 2nd switch (#2), and one side of it feeds bulb #1. The other side of this switch feeds switch #3 (another SPDT 3 way) center leg, and one side feeds bulb #2 and the other side feeds a 4th switch, and so on. No neutrals are switched, all switches are on the hot side. Someone entering the hall turns on switch #1 and bulb #1 lights. Halfway to bulb #2 is switch #2, the person switches it and bulb 1 goes out and bulb 2 comes on, and so on. This assumes! that the previous person who went down this hall returned and switched all switches back to their original positions though. If I can't count on that, then things really get messy...

I didn't have enough fuel (beer) to realy think about it last night, but came up with the same meathod wa2ise mentioned with some modification. Which I won't go into for the sake of the student.... But am wholey confident that it can be done without switching neutrals, and operate in the intended manner from either direction. Or from the same direction twice. (I have to draw it out to be sure, which will take some time, and some beer.)

Now, last night while sipping my only beer, and pondering this puzzler, I realized that I have done this problem 15+ years ago, in school. It was an epiphany! Now, without giving it away, here is two clues:

Voltage drop can be an issue

Each switch changes state twice

Now I need some beer to absolutely sure.

(Jon, what is a "French 3-way? The same as a Hollywood 3-way?)

winnie i looked into the "french three-way circuit" and wow that looks like a mess waiting to happen and see why it is illegal, but would it still be illegal if u reidentified the neutral as a hot wire?

[This message has been edited by strokezilla (edited 09-22-2005).]

OK I did it! (with no beer in the house at all...)

It could take a day to draw it up well though...

We'll wait; we have time.

Yes, because (a) you are switching the grounded conductor and (b) in one of the "on" combinations you'll have the grounded side of the supply on the center contact and the hot on the screwshell.

By using a series of cross-connected French 3-ways you could achieve the desired result easily enough. I'll sketch out the circuit when I get a few minutes to spare.

Scott,
Are you using DPDT switches at each location, each light basically on a normal 3-way so that one half of each switch forms one 3-way for the light in front and the other half is the 3-way for the light to the rear?

I'll wait to see if that's your solution before sketching that one out, but as I see it
that would work and be perfectly "legal" too. (hot side switched, screwshells all direct to the grounded conductor).

It would sure use some wire though!




[This message has been edited by pauluk (edited 09-23-2005).]

strokezilla,

So when is you're project due?

next thursday, everyone in the class is doing stuff like this to try and get help in doing it, we were tempted to open the display up, but the teacher walked around the corner when we were planning it lol, so i dont think that would be a good idea now i sure he will be watching it like a hawk.