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A. Spruce
Re: Shared Neutral question
kentvw wrote:

I think it must be a nort thing. They have some weird stuff up there. But, you see pictures of them and they at least look like fairly normal people. :D

I don't know about that, have you seen the latest issue of TOH Magazine? ;):p:D

canuk
Re: Shared Neutral question
Quote:

Yeah, and you probably have a poodle you dye pink too.

Geez .... I do not and would not.:p:D

Quote:

I don't know about that, have you seen the latest issue of TOH Magazine?

Rather handsome fellow I might say.:p:D

Ernie_Fergler
Re: Shared Neutral question
Ravens53 wrote:

I am sorry I have to disagree. This is a common practice in residential and commercial projects. But there are a few things you have to do to make this safe and code compliant.
The black and red wire must be on a two pole breaker not a twin breaker that only uses one space in the panel. The two pole breaker has one handle that turns both circuits off at the same time. It also feeds one circuit from phase A and one circuit from Phase B. Second the maximum breaker size on a #12 copper wire is 20 amps. So you can use a 15 amp breaker if you desire.If it alluminum 15 amps is the maximum size breaker
The neutral current only sees the load from each circuit at different times as they are 90 degrees out of phase.
To make it simpler AC current goes from 0 volts to 120 volts to 0 volts to -120 volts then back to 0 volts in one cycle and this happens 60 times a second. Which is 60 Hz power we use?
When phase A is 120 volts phase B is zero volts. So the neutral current on phase B is zero when Phase A is at its maximum. When Phase A is at 120 volts then phase B is 0 volts.

What I am trying to explain is the current on each phase flow at different times and the neutral only sees the current of one phase at a time.
Although there are factors when a shared neutral is not a good idea to use but that would be in a commercial application that has inductive loads that cause harmonics.

I agree with Raven53.
I also might add the phasing occurs 60 times a second, or 60hz.
And according to the 2008 NEC a two pole {two spaces} breaker is required.

Master Electrician
Re: Shared Neutral question

Multi-wire branch circuit is the correct term, and the handles must be tied together only if the hot conductors terminate on the same yoke of a device. It is permissable to feed a lighting circuit with one hot, and a string of outlets with the other, provided that the hot conductors are correctly phased.

canuk
Re: Shared Neutral question
Master Electrician wrote:

the handles must be tied together only if the hot conductors terminate on the same yoke of a device.

Would you mind explainig this a little more simply so the layperson could follow? :)

Master Electrician
Re: Shared Neutral question
canuk wrote:

Would you mind explainig this a little more simply so the layperson could follow? :)

A duplex outlet is 2 outlets on the same yolk or mounting strap. If you were to remove the tab between the 2 brass screws, you could wire each outlet to its own breaker. That being said, Now Joe Homeowner comes along and wants to replace this outlet because it's the wrong color for his new paint, He will go to the panel and turn off one breaker. That is why the NEC requires the breakers handle to be tied. Note that a piece of wire through the handles is not an approved method.

kentvw
Re: Shared Neutral question

Hmmmm............?

I believe the main reason the NEC requires a handle tie on multi wire branch circuits is because of current flow on the neutral.
You could be working on a circuit with a shared neutral with one circuit off and still have current flow on the neutral. Open that neutral and you have a shock potential.

I have warned my apprentices about this for years telling them, “You do not want to be a neutral.” I have been and it hurts. You are not only carrying the current that would normally flow through you in say a hot to ground situation, you are also carrying what ever load is on the circuit at the time.

If you think about it, it is no different than a feeder from a disconnect to a panel, and turning off only one leg of that feeder does not make much sense.

In commercial applications, systems furniture, (Office cubicles) are typically fed with four circuits. Three of those circuits share a neutral and one has a dedicated neutral. We are now required to have handle ties across all four breakers feeding these systems for the reason mentioned above.

I know, I'm from Colorado. :D :rolleyes:

Re: Shared Neutral question
kentvw wrote:

Hmmmm............?

I believe the main reason the NEC requires a handle tie on multi wire branch circuits is because of current flow on the neutral.
You could be working on a circuit with a shared neutral with one circuit off and still have current flow on the neutral. Open that neutral and you have a shock potential.

I have warned my apprentices about this for years telling them, “You do not want to be a neutral.” I have been and it hurts. You are not only carrying the current that would normally flow through you in say a hot to ground situation, you are also carrying what ever load is on the circuit at the time.

If you think about it, it is no different than a feeder from a disconnect to a panel, and turning off only one leg of that feeder does not make much sense.

In commercial applications, systems furniture, (Office cubicles) are typically fed with four circuits. Three of those circuits share a neutral and one has a dedicated neutral. We are now required to have handle ties across all four breakers feeding these systems for the reason mentioned above.

I know, I'm from Colorado. :D :rolleyes:

To add to what Kent has said the 2008 NEC has adopted that now ALL shared neutral circuit now requires handle ties or multipole breakers. Great idea if anyone has opened a neutral on a Y feed circuit by accident. I have lots of smoke and a lot of lost equipment.:eek:

kentvw
Re: Shared Neutral question
Ravens53 wrote:

To add to what Kent has said the 2008 NEC has adopted that now ALL shared neutral circuit now requires handle ties or multipole breakers. Great idea if anyone has opened a neutral on a Y feed circuit by accident. I have lots of smoke and a lot of lost equipment.:eek:

To add to what Harry said.......... LOL.

That is for sure. All current wants to do is get back to it's source. So say you have a shared neutral situation on two receptacle circuits with stuff plugged in and turned on. Then go lift the neutral off at the panel and watch what happens to the current flow. Current flow from say phase A flows from phase A through an appliance, back to the neutral wire then goes through an appliance plugged in to say phase B and back to phase B.

This is a really quick way to create a lot of smoke and blown appliances.

Ernie_Fergler
Re: Shared Neutral question
Master Electrician wrote:

A duplex outlet is 2 outlets on the same yolk or mounting strap. If you were to remove the tab between the 2 brass screws, you could wire each outlet to its own breaker. That being said, Now Joe Homeowner comes along and wants to replace this outlet because it's the wrong color for his new paint, He will go to the panel and turn off one breaker. That is why the NEC requires the breakers handle to be tied. Note that a piece of wire through the handles is not an approved method.

Thanks for the info:)

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