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Old 02-02-2010, 06:50 PM   #16
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If there is an interconnection, does it make sense that I'm getting only a 120v rating? And is it safe for now? Besides needing to know that both 6 & 26 need to be shut off to work with certain boxes?

Also, at the risk of sounding terribly stupid, what is "mwbc"?
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Old 02-02-2010, 07:10 PM   #17
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oops...MWBC = Multi-wire branch circuit
2 120v circuits that share a neutral
Each breaker supposed to be on opposite bus so power across neutral cancels/balances & handles tied together
OR a 240v breaker is used - my preference



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Old 02-02-2010, 08:02 PM   #18
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So if it is a MWBC, would it make sense that I'm reading 120v at the outlet when both breakers are on? and that both black wires are independently live?

I don't even want to tell you what I thought MWBC stood for.
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Old 02-02-2010, 08:06 PM   #19
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Yes....each outlet is split & each one is a different circuit
Only 120v
If you measure black to black you should get 240v if it is a MWBC

This shows the idea with 14-3
On the right the little brass tab is broken, seperating the 2 outlet connections (screws)





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Old 02-02-2010, 08:13 PM   #20
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That diagram makes a lot of sense. But, in the outlet I removed the tie strip was in tact on both hot and neutral side. So after removing the outlet I temporarily wire-nutted the blacks together and wire-nutted the whites together. When I measure the voltage of this config, I'm getting 120v. I'm measuring by sticking red probe in wire-nutted black wires, and black probe in wire-nutted white wires.
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Old 02-02-2010, 08:21 PM   #21
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Could be someone replaced the outlet & did not break off the strip
If the 2 hots are seperate breakers & you tie them together the breaker(s) will trip

If its the same circuit they won't



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Old 02-02-2010, 10:35 PM   #22
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Well the two hots are connected now, nothing is tripping. So I agree, intuition would suggest the are NOT on seperate circuits. Plus they read at 120v. But, as I was saying a few posts ago, one is live on 6 and the other 26, and only when they're connected to eachother does the adjacent bathroom fan and light function. What scuba Dave is saying makes sense and that's why I'm confused by the situation.

The funny thing is, this all started because some bonehead painted over the
wall plate and I broke the old outlet trying to remove the cover to paint the room. It was late and I didn't have a spare outlet so I wanted to wire-nut the circuit, go to bed, and get a new recepticle in the morning. But putting it back the way it was seemed strange and led me to these discoveries. I hate finding mysteries like this.

I REALLY appreciate everyone's help so far.
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Old 02-03-2010, 07:09 AM   #23
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With the absence of a red wire (don't remember one mentioned). I doubt this is a miswired MWBC. More likely someone crossed two hots at a junction box or switch box, luckily with both circuits on the same hot leg.

I would start tracing both circuits from the panel and try to find where they may intersect. If you want to leave this as is, I would remove the wires from each breaker, wirenut them together with a short length of wire, then attach that wire to ONE of the breakers. This places everything on the same circuit and removes some of the danger... the downside is that you may now have too much on this circuit.
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Old 02-03-2010, 07:56 AM   #24
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Quote:
Originally Posted by joshg3p0 View Post
I REALLY appreciate everyone's help so far.
Where are you located ?
1st post states this is Romex cable
Outlet broken...replaced.....2 blacks...2 whites & grounds

But you state:
Quote:
Each black wire is live from two individual breaker switches on the right side of my panel
If they are live from 2 different breakers then they would trip when connected together
So these must be from the same circuit

Quote:
When breaker 6 and 24 are off both black wires are not live
When 6 is on but 24 off, one of the black wires is live
When 24 is on, but 6 is. Off, the other black wire is live only
When 6 and 24 are both on, but the whites and blacks from each circuit are not pigtailed respectively, the light and fan in the adjacent bathroom doesn't work
Is there only 1 switch in this area ? Any other switch at all ?
What are you using to test voltages ?
You need something that reads voltage, NOT a Power/No power indicator

Are you sure where the white & black were connected on that outlet before replacing it ?
If one cable goes to the light switch might be a switch loop that is connected wrong



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Old 02-03-2010, 08:45 AM   #25
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Quote:
If they are live from 2 different breakers then they would trip when connected together
So these must be from the same circuit
Dave: They will trip if on breakers that are on opposite legs, but not two on the same leg. So, yes, technically they are on the same overall circuit, but they are being fed from two separate breakers.
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Old 02-03-2010, 08:53 AM   #26
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In the outlet box there is 2 12/2 cables coming in. I'm certain of the way they were connected to the outlet. Especially since I snipped the wires and left the trimmings connected to the outlet. And right now, the blacks are wire-nutted together (with no tripping).

I measured approx 121v with a multimeter. The outlet is not switched.. But the fan and light in the adjacent bathroom have two switches (this is what doesn't work unless 6 and 24 are ON). There are also some other switched lights and an outlet in the adjacent bathroom that are that are on breaker 6 (but they DO function when 6 is ON and 24 is OFF).

Last edited by joshg3p0; 02-03-2010 at 08:57 AM.
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Old 02-03-2010, 08:58 AM   #27
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If it's a crossed circuit. Wouldn't I measure closer to 220v at the outlet?
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Old 02-03-2010, 11:49 AM   #28
 
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With the black conductors disconnected from each other and capped off and the whites wires nutted together, does the bathroom fan run with only one of the breakers on? If so, check to see which black in the receptacle box is hot.

Although I don't believe it to be an issue in this case, the low impedance of many low cost digital VOMs can show a voltage where there really isn't one, and if it is auto ranging, make sure it hasn't switched to mV display.
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Old 02-03-2010, 02:40 PM   #29
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I'll give that a try that later tonight. Initially, I didn't want to mess with what was there, since I didn't know what the problem was (or if there really was one).
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Old 02-03-2010, 03:00 PM   #30
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Quote:
Originally Posted by Pro_DYIer View Post
Although I don't believe it to be an issue in this case, the low impedance of many low cost digital VOMs can show a voltage where there really isn't
I think you mean high impedance.

There's an easy fix for that if you have the cohones.. you can just brush the wire with the back of your hand.
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