California Three-ways

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So, Chris, given the responses, was this what you were looking for?

Reason I ask is that the basic method shown, in the responses to your question, I've always known as a Carter.

There is a "travelling bus" arrangement that requires a minimum of four wires that I was taught (as an apprentice) was called a California 3 way.

This sketch is what I was taught to be a "California" three-way as well and they are very handy if you want a hot and neutral at both switches.
 

al hildenbrand

Senior Member
Location
Minnesota
Nope, two.
Two cables are clearly allowed by 300.3(B)(3), when one includes 300.20 as needed.

However, 310.4 creates a restriction that I don't think can be gotten around.

One of the four switch states of a California 3 way results in the branch circuit hot (traveler) being in parallel with the common - common conductor. The common California 3 way is installed with #12 or #14 conductors which are too small to comply with 310.4.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
One of the four switch states of a California 3 way results in the branch circuit hot (traveler) being in parallel with the common - common conductor. The common California 3 way is installed with #12 or #14 conductors which are too small to comply with 310.4.
I don't think paralleled through switching is the same as solidly paralleled when it comes to that rule. What about two baths sharing a single fan by using two-pole switches for the lights?

Another example: with a fire-suppression system, the contacts that energize the exhaust fan (or its contactor) cause a paralleled condition if the fan is already on when there is a system trip.

To be required to break the manual control pathway when the automatic control pathway makes is like the joke about having to wake a hospital patient because it's time to take his sedative.
 

al hildenbrand

Senior Member
Location
Minnesota
I don't think paralleled through switching is the same as solidly paralleled when it comes to that rule. . .
I think you raise a great point, Larry.

However, :
310.4 Conductors in Parallel.

(A) General. Aluminum, copper-clad aluminum, or copper conductors of size 1/0 AWG and larger, comprising each phase, polarity, neutral, or grounded circuit conductor shall be permitted to be connected in parallel (electrically joined at both ends).
When the CMP chose "electrically" as the adverb in this phrase, I think they went off into a vague generalized area that reaches much wider than the common sense idea of "solidly paralleled."

You raise a great point about multiple parallel single pole switches controlling a single load.

I, personally, like the facility offered by the switching method that I illustrate in my sketch, and, given the common construction of the site assembly, see no safety issue.

The (what I call Carter) 3 way method shown in posts #4, #7 & #10 has states that cause the screw shell of the lamp holder to be energized, including one state when the lamp is not lit ("off") that are reasonably deemed hazardous. I've no problem with coaxing the rewiring of this method, as Daleuger says, to "just do it right."

But, at this point, it seems to me, 310.4 can be used to red tag any parallel single pole direct switching of a single load that is done with conductors smaller than 1/0.
 
I think you raise a great point, Larry.

However, :When the CMP chose "electrically" as the adverb in this phrase, I think they went off into a vague generalized area that reaches much wider than the common sense idea of "solidly paralleled."

You raise a great point about multiple parallel single pole switches controlling a single load.

I, personally, like the facility offered by the switching method that I illustrate in my sketch, and, given the common construction of the site assembly, see no safety issue.

The (what I call Carter) 3 way method shown in posts #4, #7 & #10 has states that cause the screw shell of the lamp holder to be energized, including one state when the lamp is not lit ("off") that are reasonably deemed hazardous. I've no problem with coaxing the rewiring of this method, as Daleuger says, to "just do it right."

But, at this point, it seems to me, 310.4 can be used to red tag any parallel single pole direct switching of a single load that is done with conductors smaller than 1/0.
Reading that made my head hurt.............
 
I just do not think 310.4 was ever intended to cover California 3-way systems. I see the intent as multiple conductors sharing a load which is larger than a single conductor can carry.

Not the case in a California such as you sketched.
 

al hildenbrand

Senior Member
Location
Minnesota
310.4 Conductors in Parallel.

(A) General.

Exception No. 1: Conductors in sizes smaller than 1/0 AWG shall be permitted to be run in parallel to supply control power to indicating instruments, contactors, relays, solenoids, and similar control devices, or for frequencies of 360 Hz and higher, provided all of the following apply:
(a) They are contained within the same raceway or cable.
(b) The ampacity of each individual conductor is sufficient to carry the entire load current shared by the parallel conductors.
(c) The overcurrent protection is such that the ampacity of each individual conductor will not be exceeded if one or more of the parallel conductors become inadvertently disconnected.
This exception is moving in the right direction, as far as I am concerned. The difficulty lies in the shopping list I highlighted in red. Expanding or altering the language would be the best approach.
 

al hildenbrand

Senior Member
Location
Minnesota
Please explain the inherent danger to life, limb or property in the three-way system that you sketched.
You see, that's just it. I agree with you that this 3 way works just fine. Back in the late '50s through the '70s a lot of high end homes were built in my area (the Twin Cities) where the wiring method was metal flexible conduit. It was rare for such a house to not to have at least one instance of this 3 way somewhere.

The reality, NEC-wise, however, is the language in 310.4 has no allowance for "intent" or for the fact that I have seen a lot of these 3 ways installed.
 
You see, that's just it. I agree with you that this 3 way works just fine. Back in the late '50s through the '70s a lot of high end homes were built in my area (the Twin Cities) where the wiring method was metal flexible conduit. It was rare for such a house to not to have at least one instance of this 3 way somewhere.

The reality, NEC-wise, however, is the language in 310.4 has no allowance for "intent" or for the fact that I have seen a lot of these 3 ways installed.
We argue over a spectrum........... I see no parallels. If anything you could argue the point of identification of a white as a return and not a hot.
 
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