three and four way swithes

[ivsenroute]

I could wire that whole thing by just using some 14/2, some duct tape a soldering iron and 4 single pole switches.:wink:

 

[MF Dagger]

I consider myself lucky to work in a large metro area (~ 3.5 M) that offers wiring methods from the beginning of AC to present. My prefered work is breathing new life into old installations, so I've had to puzzle out some fanciful switching.

I have found the "the easiest method" can seem downright alien until I get into the mind of the original installer.

No offense taken.

Many times you can see the evolution of wiring methods in the same house. It's a good place to live and work.

 

[76nemo]

I could wire that whole thing by just using some 14/2, some duct tape a soldering iron and 4 single pole switches.:wink:

And yet you'll complain when it comes time to rework ANYTHING soldered. Snip, snip, butt splice here, wirenut there

 

[al hildenbrand]

I can see it works fine but wonder why you would do it this way. . .

Dick,

I drew that diagram some years back when we (the Forum) were challenged by a member to switch the lights using a minimum of common materials.

Bennie Palmer was alive, then, and I doff my hat to him in recognition of his coining the name "Traveling Bus". :smile:

The idea was to control lights on two detached buildings with a single set of switches, and to have unswitched power at both ends, using common truck stock. Burying two 14/2 UF and doing the remainder with 14/2 & 14/3 NM does the trick. Carrying 14/4 or 14/2/2 is harder to justify as "common" truck stock. Even 14/3 UF might seem, to some, as too uncommon.

assuming the panelboard is at the house?

The beauty of this setup is that the feed can be at either end.

 

[al hildenbrand]

boy if i had to trouble shoot that i'd be swearing a lot at the original installer

I've had to do just that often enough that I finally got so I could hold the diagram in my head. In the beginning I had to draw out the diagram every time, and even remembering the diagram was hard.

The most common troubleshooting scenario is when the homeowner replaces a 3 way, and gets the common on the wrong wire. . .they get real confused, and then I have to untangle it. Sometimes they'll even try remaking the splices in the switch box. . .

When I get done, the homeowner is amazed at how quickly I did it (he spent hours fussing with it) and thinks I'm a wizard. It's great PR.

 

[Dickieboy]

Al you questioned running the circuits in RMC in regards to 300.20(B). It states specifically 1/c(i take to this mean only one 1/c and referencing choking as it passes thru the metallic wall/partition and not the conduit per se) and in my routing of 1/c's for this there would always be a return current carrying conductor so I don't see 300.20 (B) applying.

thanks for the house/barn comment,I like the running bus terminology as well

dick

 

[al hildenbrand]

Dick,

And 300.20(A)?

 

[al hildenbrand]

i take to this mean only one 1/c and referencing choking as it passes thru the metallic wall/partition and not the conduit per se

You probably know this, but I'll ask anyway. . . What causes the "choking"? The choke is an electromagnetic field that bucks the field of the current in the current carrying conductor. What causes the bucking electromagnetic field? The Eddy Current in the ferrous material surrounding the current carrying conductor. What causes the Eddy Current? The electromagnetic field of the current in the current carrying conductor. Why is it an issue with ferrous metals and not other conductive materials such as aluminum? Ferrous metals have a significantly greater magnetic permeability permitting greater flux densities thereby allowing greater induced currents. What does the induced current lead to? I?R heat losses along the Eddy Current path. How is the heat reduced? By increasing the physical length of the path (therefor, the R) the Eddy Current must travel by introducing cuts or other interruptions in the continuity of the ferrous metal.

 

[Dickieboy]

I still don't see this as a problem,motor control circuits,,lighting,plant shutdown systems etc (ground is the conduit)we run in RMC all the time,been doing it for 44 years as well as thousands of my cohorts.

Why would this be any different than a hot and a switch leg (no neutral included)dropping down the wall in conduit off a header pipe that goes on to the light?

dick

 

[al hildenbrand]

Back in post #15 you wrote:

Here is another example thats fits physically to the schematic/wiring diagram. If I were to pipe this up using all 1/C's,would there be a problem with any code violation?This of course is a bit of a different question than the OP.

As I read this, I read one conductor per pipe.

You must not be saying that. No? :-?

 

[peter d]

Why would this be any different than a hot and a switch leg (no neutral included)dropping down the wall in conduit off a header pipe that goes on to the light?

It's completely different. In the classic "switch loop" that you describe, the magnetic field is canceled out because the current on one conductor is equal to the current on the other conductor, thus no inductive heating.

 

[al hildenbrand]

Why would this be any different than a hot and a switch leg (no neutral included)dropping down the wall in conduit off a header pipe that goes on to the light?

Look at the first diagram again. The neutral and the hot run in different conduits. 300.20(A) won't allow that if the conduit is RMC (or other ferrous conduit).

 

[Dickieboy]

Hahahhahahah,no I'm saying the first sentence of 300.20(B) says that,hence the choke we spoke about.

dick

 

[al hildenbrand]

Dick,

Setting aside the 310.4 parallel conductor issue. . .(pretend just for this post that there is an exception that permits this exact "coincidental" paralleling in a 3 way and 4 way switching loop and travelers). . . The original diagram:

can only be done in a nonmetallic wiring method, or a nonferrous wiring method. 300.20. The pipe, if it is ferrous, would require a cut run the length of it (if such a thing were possible) to mitigate the Eddy Current heating.

Reverse the positions of the two 3 way switches in the diagram. The light will be on. Now, follow the currents. Even with no load downstream on the unswitched hot and neutral, there will be current in only one conductor in each of the three conduits around the switch - switch - light triangle. 300.20(A).

 

[al hildenbrand]

Hahahhahahah

:-? . . . . .

 

[al hildenbrand]

2008 NEC
300.20(B)
. . .(1) cutting slots in the metal between the individual holes through which the individual conductors pass. . .

How can one cut a slot between a hole in one box and the holes in two other boxes?

 

[Dickieboy]

Al the message disappeared on the haha post . It was written no the 1st sentence of 300.20(b) says 1/c hence the choke.

dick

 

[Dickieboy]

I don't know why this ever came to being but the intent was when a 1/c wire (one wire) passes thru a metal plate ,not a conduit opening in a metal box or within a metal conduit,lets call it a metal wall,now cut the slots in the metal wall, it relieves the concentration,thereby reducing the inductive heat buildup .

dick

 

[al hildenbrand]

Al the message disappeared on the haha post .

No, it didn't.

I'm only confused by the "Hahahhahahah".

But that's to the side of the discussion we're having.

The requirements in (1) and (2) of 300.20(B) result in the magnetic fields, around the various conductors with currents in them, being inside a common "air space" so that when the various magnetic fields are summed, the net magnetic field the ferrous metal "sees" is zero.

Hence no Eddy Current, to speak of, is induced.

 

[al hildenbrand]

the intent was when a 1/c wire (one wire) passes thru a metal plate ,not a conduit opening in a metal box or within a metal conduit,lets call it a metal wall,now cut the slots in the metal wall, it relieves the concentration,thereby reducing the inductive heat buildup.

Before you go there, please consider Charlie's Rule of Technical Reading.

While 300.20(B) deals with enclosure walls, it does not negate 300.20(A).