Junction Box Wiring

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  #41  
Old 12-04-13, 10:59 AM
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The breaker needs to match the brand of the panel. A list of breaker types will be on the label inside the panel.

You will turn off the two breakers and remove the wires. You will then install the new breaker and connect one wire to each screw.

The breaker size will depend on the wire size. #14 will is 15 amps, #12 is 20 amps.
 
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  #42  
Old 12-04-13, 11:41 AM
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The breaker is specific to your panel. There should be a list of approved breakers on a label in your panel. Sort of fits isn't good enough.

And remember Nash's post:
In order to make these circuits up to code and safe, would it be best to join with a handle tie, or 1 double pole breaker?
With a handle tie. The requirement for the two breakers protecting a MWBC is for common open, not common trip (which is what a 2-pole breaker provides).
He was refering to two single pole breakers.
 
  #43  
Old 12-04-13, 11:56 AM
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Thanks ray2047. Does a common open mean when you switch 1 breaker off both Open?

I cant seem to find a compatible handle tie for this breaker.

If an overload occured with a handle tie in place only the breaker with the overload trips. If an overload occurs with a double pole breaker both trip. Is this correct?

Isnt it safer to have both trip since they share the same nuetral?
 
  #44  
Old 12-04-13, 12:21 PM
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Does a common open mean when you switch 1 breaker off both Open?
Yes. It wold be code compliant to use a two pole breaker.
 
  #45  
Old 12-04-13, 01:25 PM
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Do I need to purchase a brand specific double pole breaker? Or will any brand due. What amperage breaker will I need?
In post #12 you showed us a picture of a Murray Type MP-T single pole breaker, do you have a Murray panel? As has already been mentioned, the breaker must match the panel.
 
  #46  
Old 12-04-13, 01:59 PM
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Yes. I checked today. It is a Murray panel.
 
  #47  
Old 12-04-13, 04:12 PM
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I think the handletie requirement is just so an unexperienced homeowner like you and I dont get zapped by the neutral when servicing one of the shared circuits. Just make sure you shut them both when you or your electrician are servicing the circuits.

I like to read what the electricians here think of the handletie requirement..

There is another reason your installing doublepole breakers besides satisfying that 2008 code requirment right?

I have a number of MWBC in my house too, no handleties, no doublepole breakers....
 
  #48  
Old 12-04-13, 04:40 PM
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Rards, the former NEC requirement has for a common disconnect only if both hots landed on the same yoke in a residential setting. Commercial setting required the common disconnect regardless of being on the same yoke.
 
  #49  
Old 12-04-13, 05:21 PM
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I think the handletie requirement is just so an unexperienced homeowner like you and I dont get zapped by the neutral when servicing one of the shared circuits.
That was the way I looked at it till I recently read an article that reminded me that pros make mistakes and get hurt too. I'll see if I can find the article and give you a link to it.


I didn't find the article, but the subject was a 26 year old apprentice who was killed when he contacted a live 277 volt circuit, part of a multiwire branch circuit. All the breakers on the circuits sharing the neutral were not shut off. The principle is the same that a homeowner might encounter on a 120/240 volt system.
 

Last edited by CasualJoe; 12-04-13 at 05:49 PM. Reason: Added a comment
  #50  
Old 12-04-13, 05:54 PM
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I'm asking this question because I'm under the assumption that if a neutral were to be disconnected somehow a double pole breaker will pop both breakers instead of just 1.

The reason I ask is I remember reading that in MWBC circuits if a neutral is disconnected in 1 circuit there is a possibility of over current in another connected circuit.

Would that in essence pop both double pole breakers?

Please clarify if I'm wrong?
 
  #51  
Old 12-04-13, 05:58 PM
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Lifting the neutral can increase the voltage on the hot legs and will fry delicate electronics.

The breakers trip from too much current either though usage or a short circuit.
 
  #52  
Old 12-04-13, 06:08 PM
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Lifting the neutral can increase the voltage on the hot legs and will fry delicate electronics.
I agree 110%. I've seen multiple desktop computers, fax machines and copy machines instantly fried when an electrician thought he was doing the right thing by not turning off any breakers in an office to tie in a new receptacle. This is just one reason reputable contractors carry insurance.

The breakers trip from too much current either though usage or a short circuit.
Yep, also agree. Overvoltage kills electronics, but doesn't trip breakers.
 
  #53  
Old 12-04-13, 06:08 PM
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So nothing will protect in that situation?
 
  #54  
Old 12-04-13, 06:13 PM
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So nothing will protect in that situation?
The only thing that will help is turning off all the circuits that share the same neutral. That's why there is a requirement for using either handle ties or multi-pole breakers on MWBCs.
 
  #55  
Old 12-04-13, 06:32 PM
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I meant if a neutral somehow became disconnected in an unknown situation, not while being serviced.

Although I'm sure that's quite rare.

And if that happened and touched ground or hot, it would then cause a short and pop a breaker?
 
  #56  
Old 12-04-13, 09:51 PM
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If the neutral became disconnected the circuit would stop functioning. If it touched ground it would continue to operate.
 
  #57  
Old 12-08-13, 09:02 AM
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If you have a voltmeter, measure the voltage between the red and the black ; it is probably 208 to 240 volts. Measure the red-white voltage, probably 110 to 120; measure the black-white voltage, probably 110-120.
So if your intent is to have a 110 volt outlet attached to red-white you are ok. And a 110 outlet to black-white you are ok.
The danger is that if you should somehow plug some shared devices, say a set top box into one outlet, and a tv, say, into the other outlet, then there could be a 208v surprise at some shared conductor ... seems far-fetched but I think that's the reason that careful electricians (which I'm not) keep outlets from the two different sides of the 220 line, each of which is 110 to neutral, distant from each other.
Presumably the two A/C's are distant from each other so the electrician felt it was no risk ...
and if you are accepting of the same level of risk (low) then you should be safe . It would be nice to know exactly what the local and national electric codes have to say on the subject ... perhaps a call to your local city hall to find out what a visit from the building inspector would entail would put your mind at ease.
 
  #58  
Old 12-08-13, 04:27 PM
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The NEC requirements for a common means of disconnect has been posted a couple of times in this thread along with the reason for it. Do you have an additional question?
 
  #59  
Old 12-08-13, 07:34 PM
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With corectly wired mutiwire circuits current on the neutral is only the difference between the amperage on the two ungrounded conductors.
  • Worst case: Current on black 20 amps - 0 amps on red=20 amps on neural.
  • Best case: Black 20 amps - red 20 amps =0 on the neutral
 

Last edited by ray2047; 12-10-13 at 02:47 PM.
  #60  
Old 12-09-13, 07:30 AM
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Please see Rays post above. Sharing the neutral is not unsafe if done correctly. The electrician did not overlook anything from what I can tell. The code has simply changed since the install.

The service to your house shares one neutral.
 
  #61  
Old 12-09-13, 07:34 AM
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Please see Rays post above. Sharing the neutral is not unsafe if done correctly.

The service to your house shares one neutral.
ray2047
No it can't. Current on the neutral is only the difference between the amperage on the two ungrounded conductors. �Worst case: Current on black 20 amps - 0 amps on red=20 amps.
�Best case: Black 20 amps - red 20 amps =0 on the neutral
Ray and Pcboss are absolutely correct. Tom42el, you must not have read the entire thread, you are wrong on this one.
 
  #62  
Old 12-09-13, 08:48 AM
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You guys scare me. The 2 circuits are sharing the same white (neutral) wire, which means it can be carrying TWICE the current it's rated for. This is a serious fire hazard, especially if 2 heavy current devices such as air conditioners are being used on these circuits.
Did the original poster confirm that his multiwire branch circuit are on opposite legs of his panel? If so, that sounds pretty standard no... which means Tom is the one scaring people?
 
  #63  
Old 12-09-13, 08:52 AM
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Opposite hots would be the correct way to wire a multi-wire branch circuit. The OP shows the two breakers stacked above each other, which would be correct.
 
  #64  
Old 12-09-13, 06:27 PM
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Tom is the one scaring people?
Everyone makes mistakes, I know I do!
 
  #65  
Old 12-19-13, 12:05 PM
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Hey everyone, I just noticed this thread continued 5 days after my last post. I do appreciate everones input in this matter.

As of now everthing is working fine. I feel comfortable with the knowledge Ive gained from everyones expertise.

And I know the job has been done correctly.

Thank you all.
 
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