Parallel switches, multiple functions

[steve66]

That is even easier then what I had proposed-- no contactor necessary. Problem is it would not be legal when two switches were on. The contactors would avoid that.

I see what you are saying: If both switches are on , the wire are in parallel, which probably would not be allowed.

That's true if we are talking about a premisis wiring system, and the loads are something other than a control relay or some type of insturmentation. And you would be right - the contactors would always be a legit install.

But if it just so happens that the source, the switches and the loads are all together in some kind of black box, then the NEC might not apply, and the swtiches just might be OK. I guess since the detail showed a DC power supply, I was thinking of something more along these lines.

 

[Dennis Alwon]

I see what you are saying: If both switches are on , the wire are in parallel, which probably would not be allowed.

That's true if we are talking about a premisis wiring system, and the loads are something other than a control relay or some type of insturmentation. And you would be right - the contactors would always be a legit install.

But if it just so happens that the source, the switches and the loads are all together in some kind of black box, then the NEC might not apply, and the swtiches just might be OK. I guess since the detail showed a DC power supply, I was thinking of something more along these lines.

You are probably correct but my mind is always thinking of nec stuff. I am curious what the OP is trying to do.

 

[BJ Conner]

And, ORs, Nors and Nands

And, ORs, Nors and Nands

No sir. Not homework, just a pet project I'm trying to figure out.

IF your doing it for fun get a good book on logic. You get into things lile
C= S1and S2 or (S1 or S3) and S2 or some such. And usually a dot and OR is a dot.
In theory you can take conditions in the real world, define states (switch open or closed) and configure circuits to do what you want.
All my books on that are put away. IF I come across any good references on the web I'll post them.
Google up circuit logic diagrams and there is some information on wickipedia.

 

[hurk27]

Steve66 has the closest for being simple and lowest cost in post 16, why complicate things?

Switch 1 DPST, contact 1 feeds load A, contact 2 feeds load C
Switch 2 DPST, contact 1 feeds load B, contact 2 feeds load C
Switch 3 SPST, contact 1 feeds load C.
Replace the above DP switches with relays and the same can be done with just single pole switch's.

All switch's are fed from same power source, all return from loads are to the same power source.

Putting the batteries in your diagram just confused every one thinking this was a DC circuit, and as you said in post 7 " Everything in the circuit runs on 120V AC. "
cleared that up or should have.

Steve would have had it right in his post but he just switched the wrong loads.

 

[hillbilly1]

That is even easier then what I had proposed-- no contactor necessary. Problem is it would not be legal when two switches were on. The contactors would avoid that.

Code reference(s) please.

 

[sameguy]

That is a control circuit just like a 3way so no problem with the code. It is not trying to increase the current capability.

 

[Dennis Alwon]

Code reference(s) please.

I was referring to 300.3(B)(1)

 

[gar]

110324-0825 EDT

rickwire1:

Going back to my post #10 and the restriction I placed on the allowed operation of the switches to provide a unique solution, and add more to the definition as follows:

Besides this information you need to define what happens to the outputs for any combination of input switches. This makes it much more complex so forget this by saying that no more than one input switch is to be asserted at any time.

Change the definition of the logic circuit to the following:
O1 = I1 and Not I2 and I3 don't care
O2 = I2 and Not I1 and I3 don't care
O3 = (I3) or (I1 and Not I2) or (I2 and Not I1)

See if you can create a circuit to fit these logical requirements. Note there is not a unique circuit, but there is at least one minimum circuit. Where minimum means the least number of switch contacts.

In the past minimization was of great importance. Consider the telephone network where multi-millions of contacts were used. Today in electronic circuits and computer programs the art of minimization has been thrown out the window for the most part. Only internal to integrated circuits is great effort expended in the minimization direction.

A classic book on switching circuit theory is:
"The Design of Switching Circuits", Keister, Ritchie, and Washburn, 1951, Van Nostrand, Bell Labs.
A more general book on logic is:
"Symbolic Logic", Irving M. Copi, MacMillan, 1954.

.

 

[sameguy]

I was referring to 300.3(B)(1)

300.3b1 sends you to 310.4 where parrallel = "electrically joined at BOTH ends to form a single conductor";
this is not a parrallel connection!

 

[LarryFine]

I still claim my answer in post 6 works.

 

[hillbilly1]

That is a control circuit just like a 3way so no problem with the code. It is not trying to increase the current capability.

That was what I was thinking.

I was referring to 300.3(B)(1)

Thanks, I will look it up when I get a chance.

 

[Dennis Alwon]

300.3b1 sends you to 310.4 where parrallel = "electrically joined at BOTH ends to form a single conductor";
this is not a parrallel connection!

I beg to differ. They end and start at the same place but take a different route getting there.

 

[hurk27]

I beg to differ. They end and start at the same place but take a different route getting there.

I agree it is a paralleled circuit, I just don't think it was the intent of the NEC to disallow this, I see no danger in a circuit like this as I have many time done similar for a common bath exhaust fan servicing two or more bathrooms, the fact that each individual conductor is still protected at it's branch circuit rating removes any danger that otherwise would be presented like in a parallel circuit where conductors are paralleled to increase the capacity of the circuit, I think 310.4 needs to be expanded to allow this just as they did in the exception under (b) and (c)

 

[sameguy]

I beg to differ. They end and start at the same place but take a different route getting there.

It looks to me that they are under control not a static connection at both ends with the intent to create a single wire.
As I quoted per code.

I changed this due to trying to keep on OP drawing.

 

[gar]

110325-1325 EDT

rickwire1:

Can you provide more information on what was your goal with the original post? It seemed to me you were asking a logic question and not an NEC question.

Based on what has been said over the various posts can you write a complete description of what you want the circuit to do, and any limitations on the circuit? This can be done as a set of truth tables.

Note: the third load device in your circuit drawing has three states and therefore you have to invent someway to cover this in the truth tables, if you use truth tables.

.

 

[hurk27]

110325-1325 EDT

rickwire1:

Can you provide more information on what was your goal with the original post? It seemed to me you were asking a logic question and not an NEC question.

Based on what has been said over the various posts can you write a complete description of what you want the circuit to do, and any limitations on the circuit? This can be done as a set of truth tables.

Note: the third load device in your circuit drawing has three states and therefore you have to invent someway to cover this in the truth tables, if you use truth tables.

.

Gar if we read between the lines of post 1 and post 7 and ignore the diagram he provided we can see that he wants to switch loads A and C together using one switch, then loads B and C together on a second switch, then just switch load C with another switch, and since the OP states that all loads are 120 volts AC, DC circuits shouldn't come into play?

I mean sure if we want to get elaborate and design a logic/processor control system to switch these loads it can be done, and there are many products on the market already that can even automate it to the point of never having to touch a switch again, but I'm not so sure if this is what the OP is requesting?

Maybe I have had the phrase "KISS" drilled into me for too long, as I also love the aspect of design, and in my work do allot of it when faced with control challenges, but at the same time I try to do more with the least amount of resources that will achieve the same function reliably.

 

[gar]

110325-1636 EDT

hurk27:

In posts 1 and 7 he uses the word AC, but in the circuit diagram of post 1 he shows a DC source.

In his circuit diagram he uses SPST switches. Is this a requirement? We do not know.

Does he require the same voltage on each load when it is energized independent of what switches are asserted? We don't know.

Are there any restrictions on the combination of switches that can be asserted? We don't know.

Nor do we know any other restrictions he may have.

The problem is the statement of the problem is incomplete. Too many unknowns and that makes assumptions very risky.

.