A bit of theory vs application

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I have a question on my mind and have gone through the theory that is applicable, but just want to check myself to make sure my thinking is correct.

A 3 wire single phase circuit that is balanced will carry a neutral load of zero. Each wire MUST be from a different phase otherwise the current is additive due to the same polarities.

Now let's say a two wire circuit is pulled from the panel into a box. From this two wire circuit a three wire circuit is created. Since the origination of these two wires is from a single phase would it not be proper to deduce that the current on the neutral of this circuit will now be additive. Thus if this were a 20amp protected circuit and each ungrounded conductor from the box were connected to a 10 amp load that would make the neutral now carry a 20 amp load. My thought goes further in that if each ungrounded conductor is now connected to a 15amp load that puts 30 amps on the conductor and we have now exceeded the ampere rating of this conductor in theory.

Are my thoughts correct and if this is correct in theory is this how an application of this sort would play out in our everyday application purposes?

Thanks for any insight that might be able to be given.
 
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HMMM....guess I did not think everything through. I guess if the original circuit was protected at 20amps then the two conductors from the box could not be put on 15 amp loads, thus negating the ability of the neutral from carrying 30amps.

Is this correct?
 

ActionDave

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A 3 wire single phase circuit that is balanced will carry a neutral load of zero. Each wire MUST be from a different phase otherwise the current is additive due to the same polarities.
Now let's say a two wire circuit is pulled from the panel into a box. From this two wire circuit a three wire circuit is created. Since the origination of these two wires is from a single phase .....
I'm confused about the part I hi-lighted in red. How would you go about doing this?
 

Smart $

Esteemed Member
Location
Ohio
DelightedInYahweh is correct. The ungrounded conductors total current would be limited by the circuit ocpd.

Your suggested 3-wire "extension" seems like it would be in violation of a wiring method... but I can't think of any at present.
 

liquidtite

Senior Member
Location
Ny
when you say two wire what comes to mind for me means one hot and a nuetral.i thought you can only have a unbalanced circuit on a mwbc?.and if it were 240vtwo wire you usually dont need a nuetral so im confused
 
Sorry everyone for my vague explanation. I was pouring out my thoughts too quickly. Let me try again.

I came across this in a house I was sent to troubleshoot some issues in and have been a bit bothered by it. Been going through what could possibly be wrong/dangerous with this application. So I posted here to get other brains looking at it from maybe different perspectives to see what help I can get. Here goes.

A 12/2 is run from the panel as a simple two wire circuit i.e. hot and neutral on a 20amp circuit. It is pulled into a switch box. At the switch box a 12/3 is begun. The red and black is connected to the hot on the 12/2 and of course neutral to neutral. Now the red goes to a switch which in turn feeds one side of a circuit of receptacles. The black feeds the other side. The tab is broken as should be to accommodate the split receptacle circuits.

It is just the issue of coming out of the box with a twelve three from a twelve two, but maybe it's just the fact that there are two colors and my mind 'wants' there to be something wrong. We 'split' the circuit up all the time to run to a light and then off to a receptacle. Maybe I am just thinking too 'hard' about it.
 

Hv&Lv

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Sorry everyone for my vague explanation. I was pouring out my thoughts too quickly. Let me try again.

I came across this in a house I was sent to troubleshoot some issues in and have been a bit bothered by it. Been going through what could possibly be wrong/dangerous with this application. So I posted here to get other brains looking at it from maybe different perspectives to see what help I can get. Here goes.

A 12/2 is run from the panel as a simple two wire circuit i.e. hot and neutral on a 20amp circuit. It is pulled into a switch box. At the switch box a 12/3 is begun. The red and black is connected to the hot on the 12/2 and of course neutral to neutral. Now the red goes to a switch which in turn feeds one side of a circuit of receptacles. The black feeds the other side. The tab is broken as should be to accommodate the split receptacle circuits.

It is just the issue of coming out of the box with a twelve three from a twelve two, but maybe it's just the fact that there are two colors and my mind 'wants' there to be something wrong. We 'split' the circuit up all the time to run to a light and then off to a receptacle. Maybe I am just thinking too 'hard' about it.
I can see why someone would look at this and just "want" it to be wrong. Electrically though, the original 12/2 feed is protected by a 20 amp OCPD. From there, no matter how many wires come from that original feed, whether it be your 12/3 or as many as you want, the new circuit(s) will be protected at 20 amps also. Even if you put 30 amp OCPD on each wire, the 20 amp OCPD will protect the entire circuit.

Think of the 20 amp OCPD as a main breaker, then feed whatever you want below it. 20 amps is all you are going to get. What goes in must come out, so 20 amps on the neutral also...

Now, is it OK with code? Still racking my brain on this one.
 

realolman

Senior Member
Sorry everyone for my vague explanation. I was pouring out my thoughts too quickly. Let me try again.

I came across this in a house I was sent to troubleshoot some issues in and have been a bit bothered by it. Been going through what could possibly be wrong/dangerous with this application. So I posted here to get other brains looking at it from maybe different perspectives to see what help I can get. Here goes.

A 12/2 is run from the panel as a simple two wire circuit i.e. hot and neutral on a 20amp circuit. It is pulled into a switch box. At the switch box a 12/3 is begun. The red and black is connected to the hot on the 12/2 and of course neutral to neutral. Now the red goes to a switch which in turn feeds one side of a circuit of receptacles. The black feeds the other side. The tab is broken as should be to accommodate the split receptacle circuits.

It is just the issue of coming out of the box with a twelve three from a twelve two, but maybe it's just the fact that there are two colors and my mind 'wants' there to be something wrong. We 'split' the circuit up all the time to run to a light and then off to a receptacle. Maybe I am just thinking too 'hard' about it.
Splicing 2 conductors to one conductor and THEN running TO a switch doesn't make much sense to me. . I would do it in the enclosure containing the switch in the form of a pigtail.... or something with individual conductors... would not be done with 12/3.

I don't think you're supposed to parallel conductors that small, although it doesn't appear to have been done for ampacity reasons... just wanted to get rid of some copper.;)


I guess if the original circuit was protected at 20amps then the two conductors from the box could not be put on 15 amp loads, thus negating the ability of the neutral from carrying 30amps.
I think perhaps the word necessity could be substituted for ability. I believe everything else you stated in your first two posts to be correct.
 

ceb58

Senior Member
Location
Raeford, NC
Sorry everyone for my vague explanation. I was pouring out my thoughts too quickly. Let me try again.

I came across this in a house I was sent to troubleshoot some issues in and have been a bit bothered by it. Been going through what could possibly be wrong/dangerous with this application. So I posted here to get other brains looking at it from maybe different perspectives to see what help I can get. Here goes.

A 12/2 is run from the panel as a simple two wire circuit i.e. hot and neutral on a 20amp circuit. It is pulled into a switch box. At the switch box a 12/3 is begun. The red and black is connected to the hot on the 12/2 and of course neutral to neutral. Now the red goes to a switch which in turn feeds one side of a circuit of receptacles. The black feeds the other side. The tab is broken as should be to accommodate the split receptacle circuits.

It is just the issue of coming out of the box with a twelve three from a twelve two, but maybe it's just the fact that there are two colors and my mind 'wants' there to be something wrong. We 'split' the circuit up all the time to run to a light and then off to a receptacle. Maybe I am just thinking too 'hard' about it.
It would be no different than landing 2 conductors on a single breaker, which most will allow. If and /or when the circuit has reached its limit the OCP will take it out, unless its a FPE, but that's another discussion.
The situation you describe is a normal one for switching a receptacle.
and yes, some times we tend to "over think" things but it is better than not thinking at all.:happyyes:
 
Guys you all have been great!!!! Makes me chuckle at myself on the inside when I stop and just say 'Adam you are thinking WAAAAYYYY too hard!! STOP IT' :lol: !!

Thanks for everything, and IF anyone thinks of something code wise I am open:cool:. But I am sure it is a mute point considering the 20amp OCPD.
 

kwired

Electron manager
Location
NE Nebraska
Sorry everyone for my vague explanation. I was pouring out my thoughts too quickly. Let me try again.

I came across this in a house I was sent to troubleshoot some issues in and have been a bit bothered by it. Been going through what could possibly be wrong/dangerous with this application. So I posted here to get other brains looking at it from maybe different perspectives to see what help I can get. Here goes.

A 12/2 is run from the panel as a simple two wire circuit i.e. hot and neutral on a 20amp circuit. It is pulled into a switch box. At the switch box a 12/3 is begun. The red and black is connected to the hot on the 12/2 and of course neutral to neutral. Now the red goes to a switch which in turn feeds one side of a circuit of receptacles. The black feeds the other side. The tab is broken as should be to accommodate the split receptacle circuits.

It is just the issue of coming out of the box with a twelve three from a twelve two, but maybe it's just the fact that there are two colors and my mind 'wants' there to be something wrong. We 'split' the circuit up all the time to run to a light and then off to a receptacle. Maybe I am just thinking too 'hard' about it.
That is not a multiwire branch circuit or even an attempt at being one that went wrong. It is one two wire branch circuit that has been split into two segments with a control device in one of the segments. Neutral in the "home run" carries equal current to the ungrounded conductor. Never any more, never any less. When the ungrounded does split the two sections of it never sum up to a different value than what the neutral is carrying. (except for abnormal situations involving ground faults).
 

charlie b

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I don't think you're supposed to parallel conductors that small, although it doesn't appear to have been done for ampacity reasons. . . .
This is not a parallel circuit. The black and red wires are connected to each other at one end, but not at the other. This is a legal install. Perhaps not a conventional install, but legal.
 

realolman

Senior Member
This is not a parallel circuit. The black and red wires are connected to each other at one end, but not at the other. This is a legal install. Perhaps not a conventional install, but legal.
That's true.:ashamed: Threw me a curve when they used two conductors of 12/3 to go from one box to another. I think "not conventional" is a generous term.
 

kwired

Electron manager
Location
NE Nebraska
That's true.:ashamed: Threw me a curve when they used two conductors of 12/3 to go from one box to another. I think "not conventional" is a generous term.
What is so "unconventional" about it. This is a practice that was very popular in 1960's and 1970's. Switch half the room receptacles and leave the other half hot all the time. That is exactly what he was describing. From the switch location it is split into switched and unswitched and a common neutral.
 

realolman

Senior Member
What is so "unconventional" about it. This is a practice that was very popular in 1960's and 1970's. Switch half the room receptacles and leave the other half hot all the time. That is exactly what he was describing. From the switch location it is split into switched and unswitched and a common neutral.

Yeah ... FROM the switch location with 12/3 to the receptacles..... not TO the switch location on two separate conductors of 12/ 3 ... that's what's weird
 

kwired

Electron manager
Location
NE Nebraska
Yeah ... FROM the switch location with 12/3 to the receptacles..... not TO the switch location on two separate conductors of 12/ 3 ... that's what's weird
I read it as saying there is 12-2 from source to switch, and 12/3 from switch to receptacles. No 12/3 on supply side of switch. The red wire you are questioning appears to me to be a pigtail within the switch box that is connected from the black to the supply side of switch.
 

realolman

Senior Member
I read it as saying there is 12-2 from source to switch, and 12/3 from switch to receptacles. No 12/3 on supply side of switch. The red wire you are questioning appears to me to be a pigtail within the switch box that is connected from the black to the supply side of switch.

A 12/2 is run from the panel as a simple two wire circuit i.e. hot and neutral on a 20amp circuit. It is pulled into a switch box. At the switch box a 12/3 is begun. The red and black is connected to the hot on the 12/2 and of course neutral to neutral. Now the red goes to a switch which in turn feeds one side of a circuit of receptacles. The black feeds the other side.
Maybe you're right. I dunno. I would not call it a 12 /3 if it is not in a sheath. I don't see much of a question if it's a pigtail. Actually I don't see much of anything. .... sorry I responded.
 

realolman

Senior Member
It is a Romex NM-B sheathed 12-3. The red and black are wire nutted to the hot wire of the 12-2. Red goes to switch, black to one side of the receptacles. Red then goes from switch to the other side of the receptacles.
There is 12/3 romex in the sheath in the same box as the switch?:?
 
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