Need help with this circuit.

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Aweitzmann7

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So to start off I am currently in school for electrical work and this is a project my teacher gave me during the week. Therefore the restrictions are not able to be changed, if they were I could do this circuit it minutes. I have racked my brain about this for hours and just can not seem to figure it out.

Device boxes A and B are switches which control there corresponding lights. The restrictions I was given were; 3 wire must be used between boxes A and B, and only wire shown in the drawing can be used (ie; a cable can not be ran between light A and light B). I know the circuit can be done and will not violate anything in the 2011 code. I'm not one to let something like this go, its going to be driving me nuts until I get it so thanks in advance guys.
WIN_20140405_140731.JPG
 
Are these supposed to be 3 way switches??? If so- it ain't going to work. If they are single pole switches then it is simple. ????? are the lights supposed to work if either switch is turned on?
 
Can't be done by conventional wiring.

You'd need a hot, two switch legs (A and B), and a neutral between boxes.
 
140405-2329 EDT

Use two SPST switches. Run a neutral between both switch boxes.

At light B and switch A connect hot to light B, and run a wire from the neutral side of light B to one side of switch B with the other side of switch B connected to neutral at switch B location.

Connect the neutral side of light A to neutral at B switch location. The hot side of light A connects to a wire to one side of switch A and the other side of switch A connects to the hot supply at switch A location.

The currents balance so there is no major external magnetic field. Does switching the neutral side of a light violate NEC?

Not a good circuit for someone to troubleshoot in the future if that troubleshooting person did not design the circuit. Nor is it really a safe circuit for troubleshooting by someone unfamiliar with the circuit.

I always like common (neutral) to always connect directly to loads and all switching be in the non-common circuitry. Common is anything that I consider my reference point. Usually ground (earth), neutral, or machine chassis is my common. But it does not necessarily mean that common is at ground or neutral potential. In the days of ACDC radios this might mean common, radio chassis, was actually connected to the hot side of the AC input. This was dependent on which way the plug was inserted in the socket. Usually if the hot side was connected to the radio chassis there was more hum in the audio output. When working on such a radio you wanted to make sure that the chassis was not hot by appropriately inserting the AC plug.

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gar said:
140405-2329 EDT

Use two SPST switches. Run a neutral between both switch boxes.

At light B and switch A connect hot to light B, and run a wire from the neutral side of light B to one side of switch B with the other side of switch B connected to neutral at switch B location.

Connect the neutral side of light A to neutral at B switch location. The hot side of light A connects to a wire to one side of switch A and the other side of switch A connects to the hot supply at switch A location.

The currents balance so there is no major external magnetic field. Does switching the neutral side of a light violate NEC?

Not a good circuit for someone to troubleshoot in the future if that troubleshooting person did not design the circuit. Nor is it really a safe circuit for troubleshooting by someone unfamiliar with the circuit.

I always like common (neutral) to always connect directly to loads and all switching be in the non-common circuitry. Common is anything that I consider my reference point. Usually ground (earth), neutral, or machine chassis is my common. But it does not necessarily mean that common is at ground or neutral potential. In the days of ACDC radios this might mean common, radio chassis, was actually connected to the hot side of the AC input. This was dependent on which way the plug was inserted in the socket. Usually if the hot side was connected to the radio chassis there was more hum in the audio output. When working on such a radio you wanted to make sure that the chassis was not hot by appropriately inserting the AC plug.

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Click to expand...
Thank you so much, i knew once i saw it i would kick myself. Really appreciate your help
 
140406-0543 EDT

Aweitzmann7:

Following is a method that does not switch neutral, and is probably a valid solution given the very loose restrictions on the solution.

Both hot and common (neutral or grounded) are present at both switch boxes. This requires two of your three wires. Therefore, the one remaining conductor has to be time shared or in some fashion used as a control line.

One simple method uses 4 diodes. At both lights the common lead (neutral or grounded) is connected to the common conductor. At each light a diode is connected from the control line to the light hot terminal. At light B the diode cathode is connected to the light's hot terminal, and the reverse polarity at light A. Note: the statement of the problem did not say DC could not be applied to the lights or that full average voltage was required. Nor did it say that the source voltage could not be AC.

At each switch location is a SPST switch connected to the hot supply conductor. In series with each SPST switch is a diode connected so that switch A controls power flow to light A, switch B power flow to light B.

This arrangement is limited to two lights and many swithes, but the switch logic would be a wired "OR" circuit. Meaning one or more switches could turn on light X, but all of those controlling switches would have to be off to turn off light X.

Much better control could be obtained with more than two lights and many controlling switches where electronics were located at each light, and the third interconnecting conductor was used as a common bus for coded control signals. This method even allows using 2 wires instead of 3 wires between switch boxes.

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I figure that the trick is to run the circuit as gar suggests, but come up with some method where you don't actually have a neutral to get around the restriction on switching the neutral.

For example, run the system with 12V ungrounded, so that you don't have any restriction on which conductor gets switched.

With that said, you could use the following method:
The 3 wire cable has 2 switched hots and 1 neutral. Call them 'Hot A', 'Hot B' and 'N'.

If 'Hot A' is fed from the supply, then light A gets turned on. If 'Hot B' is fed from the supply, then light A stays off.

At switch B, you selectively connect Hot A and Hot B. If _both_ are live, then light B turns on.

Switch A is then just a '4 way' switch, connecting supply to either 'Hot A' or 'Hot B' and connecting the feed to light B to the other 'Hot'.

The problem is at switch box B, where you would need a clever relay to determine which of the two switched hots is the 'feed' and which is being fed.

-Jon
 
Aweitzmann7 said:
So to start off I am currently in school for electrical work and this is a project my teacher gave me during the week. Therefore the restrictions are not able to be changed, if they were I could do this circuit it minutes. I have racked my brain about this for hours and just can not seem to figure it out.

Device boxes A and B are switches which control there corresponding lights. The restrictions I was given were; 3 wire must be used between boxes A and B, and only wire shown in the drawing can be used (ie; a cable can not be ran between light A and light B). I know the circuit can be done and will not violate anything in the 2011 code. I'm not one to let something like this go, its going to be driving me nuts until I get it so thanks in advance guys.
Click to expand...

There's probably something wrong with this idea, but I don't have the code in front of me.

The circuit and lights are 208V. Phase A and B are brought to the first switch box (2 wires.) A is connected to a single pole switch, and switched A, and unswitched B are run to the second switch box (2 wires, the 3rd wire is mentioned later.) At the second switch box, B is connected to a single pole switch. Switched B is run back to the first switch box (that is the third wire.) At the first switch box, unswitched A and switched B are run to fixture B (2 wires.) At the second switch box, switched A and unswitched B are run to fixture A (2 wires.)
 
david luchini said:
There's probably something wrong with this idea, but I don't have the code in front of me.

The circuit and lights are 208V. Phase A and B are brought to the first switch box (2 wires.) A is connected to a single pole switch, and switched A, and unswitched B are run to the second switch box (2 wires, the 3rd wire is mentioned later.) At the second switch box, B is connected to a single pole switch. Switched B is run back to the first switch box (that is the third wire.) At the first switch box, unswitched A and switched B are run to fixture B (2 wires.) At the second switch box, switched A and unswitched B are run to fixture A (2 wires.)
Click to expand...
That works with the exception the diagram has a half hash for one wire in each cable. Even using cables with a re-identified white conductor, the diagram would/should not show a half hash (JMO).
 
140407-0840 EDT

Aweitzmann7:

We need to know the exact statement of the problem, any specified assumptions, and any assumed assumptions.

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I have not read through the previous comments, because I do not understand the question.
  • What is represented by the two circles with the letters A and B in them?
    • Are they separate power sources?
    • Are they separate phases of the same power source?
    • Are the circles intended to represent the lights?
  • What is meant by the short lines next to what I presume to be wires?
    • Are the long lines intended to mean a phase conductor, and the shorter lines intended to mean neutral conductor, and are the ground wires simply presumed to be in addition to these?
  • What do you mean by saying the boxes with the A and B letters are switches?
    • Is the puzzle, in part, to discover what types of switches will satisfy the given restrictions?
    • Are we supposed to figure out which wires connect to which terminals on which switch?
  • What is meant by the line going down and to the left from box A, with what looks to me like an arrow?
    • Is this the return line to one of the sources, and if so what about the return line to the other source?
    • Is this the line that feeds one of the lights? If so, what about the feed to the other light?
    • Is this the single power source that feeds both lights?

 
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