Using 3-12 wire for 2 plug ins - Electrical Questions. Read Only. No more posting. - PlanetChristmas! Forums. Read Only. We've moved to http://talk.planetchristmas.com - The Forums of PlanetChristmas have moved to http://talk.PlanetChristmas.com
Sharing a neutral in this case can be safe -- as long as each hot is on an opposite phase. What I don't know is if the NEC approves of doing what you are asking for branch circuits.
When on opposite phases, the maximum return current on a shared neutral is limited to the maximum single circuit current. If you you pulled both hots from the SAME phase, then the maximum return current would be TWICE the single circuit current. I wrote a very long post on this about 6 months ago here. Unfortunately with the search as it around here, I doubt it can be found.
I would consult with an electrician who can guide you to safely doing what you want to do.
I think what he is trying to do is to use a three wire to carry two circuits. A typical three wire has a white , black, and green or bare wire. One 20 amp breaker on the white, the other 20 amp on the black, the combined nuetrals on the green or bare at 40 Amps, not a good idea at all. Does this anwer your question?
Under no circumstances can you have a shared neutral on non multi-wire branch circuits. This is a serious NEC code violation, the only way you can have a shared neutral on a branch circuit is for a multi-wire circuit i.e. a circuit operating at 230 VAC or higher either single or three phase.
Not to mention it is extremely dangerous because when using a shared neutral as you describe if you turn off one breaker and not the other and you disconnect the neutral wire you have full potential between the disconnected neutral wire and ground. This is true regardless of which pole each breaker is on.
Tony
____________________ Do not meddle in the affairs of dragons, for you are crunchy and taste good with ketchup.
FYI... Just because what you want to do is on 2 breakers does not mean they are on separate phases. While I support DIY, you may want to consider calling an electrician until you get a little more experience.
Tony:
You could use 12/4 for this tho, right (allowing for a pair of hots and a pair of neutrals)?
Last edited on Sunday March 30th, 2008 10:17 pm by oldcqr
Under no circumstances can you have a shared neutral on non multi-wire branch circuits. This is a serious NEC code violation, the only way you can have a shared neutral on a branch circuit is for a multi-wire circuit i.e. a circuit operating at 230 VAC or higher either single or three phase.
Not to mention it is extremely dangerous because when using a shared neutral as you describe if you turn off one breaker and not the other and you disconnect the neutral wire you have full potential between the disconnected neutral wire and ground. This is true regardless of which pole each breaker is on.
Tony
Thansk Tony, I should have asked you first. I didn't think I could. I was sure I seen something somewhere showing how to do that, just couldn't remember where.
Daniel Hall wrote: Are you trying to use 12-3 w/grnd ?
If this is the case yes you can share the neutral, as long as both hot wires are on opposite phase's
Black phase - A
Red phase -B
White Neutral - Neutral bar
Ground - ground bar ( only on the neutral bar if this is the main service)
You will also need to use a two pole breaker.
NO NO NO NO NO,
What you have described is a multi-wire circuit i.e. 240 VAC and unless you specifically use a double pole breaker it is against code, no exceptions period.
The type of wire you use DOES NOT determine your circuit type, the circuit type is determined by usage i.e. is this serving receptacles or a dedicated appliance or sub panel that requires a multi-wire circuit.
Grounds go to a seperate ground bar in any panel, the difference is in bonding of the neutral in a sub panel.
____________________ Do not meddle in the affairs of dragons, for you are crunchy and taste good with ketchup.
What you have described is a multi-wire circuit i.e. 240 VAC and unless you specifically use a double pole breaker it is against code, no exceptions period.
The type of wire you use DOES NOT determine your circuit type, the circuit type is determined by usage i.e. is this serving receptacles or a dedicated appliance or sub panel that requires a multi-wire circuit.
Grounds go to a seperate ground bar in any panel, the difference is in bonding of the neutral in a sub panel.
So, are you saying that the following example right out of the 2008 NEC handbook is illegal? In the dorms where I work, we have many circuits wired like this from when the houses were built. Back then they used individual breakers for each phase (some use three phases with one neutral for recepticales.) Now you must use a breaker with a common trip.
What you have described is a multi-wire circuit i.e. 240 VAC and unless you specifically use a double pole breaker it is against code, no exceptions period.
The type of wire you use DOES NOT determine your circuit type, the circuit type is determined by usage i.e. is this serving receptacles or a dedicated appliance or sub panel that requires a multi-wire circuit.
Grounds go to a seperate ground bar in any panel, the difference is in bonding of the neutral in a sub panel.
So, are you saying that the following example right out of the 2008 NEC handbook is illegal? In the dorms where I work, we have many circuits wired like this from when the houses were built. Back then they used individual breakers for each phase (some use three phases with one neutral for recepticales.) Now you must use a breaker with a common trip.
Ok here is the reason I am asking. I went and took some pics. My neutral bus bar only has 19 slots. It was fine before because they never used all of the spaces for breakers. I added 3 - 20Amp breaker at the bottom. You can see the 3 spares.
Here is the tag inside the box
My bus bars that don't have enough room for the neutrals. Only have 2 openings and need 3 spots.
Now is replacing the neutral bus bar a big job on this?
Last edited on Monday March 31st, 2008 01:49 am by bdeditch
Since you already have a 200A service you'd be better off upgrading to a 200A 42 circuit panel. It will give you more than enough capacity for future growth as well as clean up a messy panel.
Tony
____________________ Do not meddle in the affairs of dragons, for you are crunchy and taste good with ketchup.
What you have described is a multi-wire circuit i.e. 240 VAC and unless you specifically use a double pole breaker it is against code, no exceptions period.
The type of wire you use DOES NOT determine your circuit type, the circuit type is determined by usage i.e. is this serving receptacles or a dedicated appliance or sub panel that requires a multi-wire circuit.
Grounds go to a seperate ground bar in any panel, the difference is in bonding of the neutral in a sub panel.
So, are you saying that the following example right out of the 2008 NEC handbook is illegal? In the dorms where I work, we have many circuits wired like this from when the houses were built. Back then they used individual breakers for each phase (some use three phases with one neutral for recepticales.) Now you must use a breaker with a common trip.
What you have to realize is that to apply that specific section and example from the NEC requires that you follow each and every rule and reference that 210.4 designates.
To explain in detail here how to properly install and wire a multi-wire circuit in this forum would be next to impossible as well as not having explicit and direct knowledge of the actual installation location I would not personally or professionally try to do do so.
Based on keeping people safe and making sure that the average homeowner not attempt something that can easily be installed incorrectly I don't recommend using the described and detailed method.
While the NEC does allow multi-wire circuits, with the new Arc fault requirements this won't work because they are not producing AFCI breakers with a common trip.
Tony
____________________ Do not meddle in the affairs of dragons, for you are crunchy and taste good with ketchup.
What you have described is a multi-wire circuit i.e. 240 VAC and unless you specifically use a double pole breaker it is against code, no exceptions period.
The type of wire you use DOES NOT determine your circuit type, the circuit type is determined by usage i.e. is this serving receptacles or a dedicated appliance or sub panel that requires a multi-wire circuit.
Grounds go to a seperate ground bar in any panel, the difference is in bonding of the neutral in a sub panel.
So, are you saying that the following example right out of the 2008 NEC handbook is illegal? In the dorms where I work, we have many circuits wired like this from when the houses were built. Back then they used individual breakers for each phase (some use three phases with one neutral for recepticales.) Now you must use a breaker with a common trip.
What you have to realize is that to apply that specific section and example from the NEC requires that you follow each and every rule and reference that 210.4 designates.
To explain in detail here how to properly install and wire a multi-wire circuit in this forum would be next to impossible as well as not having explicit and direct knowledge of the actual installation location I would not personally or professionally try to do do so.
Based on keeping people safe and making sure that the average homeowner not attempt something that can easily be installed incorrectly I don't recommend using the described and detailed method.
While the NEC does allow multi-wire circuits, with the new Arc fault requirements this won't work because they are not producing AFCI breakers with a common trip.
Tony
Cost wise I rather not. I don't need much growth beyond the 3 20 Amp breakers. I have a 30 Amp gifi that is never used as well
12-2 wire is usually white, black & ground
3 wires but it is called 12-2
12-3 wire is usually white, black, red & ground - 4 wires
It used to be common practice to run 12-3 for 2 circuits & use (2) single breakers
Code has changed, they now want a double pole breaker as Tony stated
But now they also want AFCI breakers
I don't have a 2008 book yet
You are allowed (depending upon the panel) to couble up GROUNDs
It looks like they have already been doing this in your panel
Check to see if your panel allows doubled up grounds - they must be the same gauge.
Neutrals I have never doubled & my understanding is most panels do not allow this
David Balch wrote: 12-2 wire is usually white, black & ground
3 wires but it is called 12-2
12-3 wire is usually white, black, red & ground - 4 wires
It used to be common practice to run 12-3 for 2 circuits & use (2) single breakers
Code has changed, they now want a double pole breaker as Tony stated
But now they also want AFCI breakers
I don't have a 2008 book yet
You are allowed (depending upon the panel) to couble up GROUNDs
It looks like they have already been doing this in your panel
Check to see if your panel allows doubled up grounds - they must be the same gauge.
Neutrals I have never doubled & my understanding is most panels do not allow this
I prefer to never run a multi-circuit wire
Thats understandable, but is it a lot of work to replace the neutral and grounding bars to have more wires?
