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Old 11-24-2013, 09:56 AM   #21
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Im not an electrican (yet) so dont rip me a new one for not totally grasping this.

Quote:
It is the outlets after the open neutral but before the split that causes the problems. Devices plugged into these outlets will backfeed the voltage from both phases onto the neutral back to the point where it has been accidently opened. It can now overvoltage/undervoltage beyond the split and the devices plugged into those outlets can contribute to the problem as well.
I understand now that a neutral opening at the outlets on either leg after the split would not cause the voltage imbalance.

But just to clarify after reading the above explanation, In the case of a neutral breaking prior to the spilt,

Quote:
Devices plugged into these outlets......
This makes it sound like only loads plugged in prior to the split cause the voltage imbalance on the other 2 legs of the MWBC.

However, I assumed that If the neutral breaks prior to the split, (even if there are NO outlets/loads plugged in prior to the split), then each leg after the split now will have the voltage imbalance between each other.

In other words, if the neutral opens prior to the split, my TV and Lightbulbs after the split are toast.....

Again, I am a minor and a student... please be kind.
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Old 11-24-2013, 10:12 AM   #22
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That's right they're toast,so that's why we pig tail it to the receptacles .
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Old 11-24-2013, 12:01 PM   #23
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Quote:
Originally Posted by soe View Post
This makes it sound like only loads plugged in prior to the split cause the voltage imbalance on the other 2 legs of the MWBC.

Loads after the split also have an effect but only if the break is before the split.

However, I assumed that If the neutral breaks prior to the split, (even if there are NO outlets/loads plugged in prior to the split), then each leg after the split now will have the voltage imbalance between each other.

Yes

In other words, if the neutral opens prior to the split, my TV and Lightbulbs after the split are toast.....

Yes

Again, I am a minor and a student... please be kind.
.....

Last edited by 8V71; 11-24-2013 at 02:50 PM. Reason: corrections
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Old 11-24-2013, 01:27 PM   #24
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8V71 - Thank you very much. That is exactly what I was unclear about.

TO summarize what I 'think' I have gathered from your reply.... in my crude drawing below......



A break in the neutral at the yellow X, will NOT send unbalanced 240 over L1 and L2 unless there was a load at outlet 1 (prior to break).

Remove outlet #1 from equation completely... breaking the neutral now... both L1 and L2 circuits would be dead, not turn them into a 240 ciruit together.

THat is why we pigtail that outlet #1.... and even if that pigtail connetion failed (say the X break is the pigtail), then both L1 and L2 circuits would be dead (no overvoltage situation).

Thanks for your patience with me... let me know if my reasoning is correct.

Happy Thanksgiving.
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Old 11-24-2013, 01:30 PM   #25
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Quote:
Originally Posted by soe View Post
8V71 - Thank you very much. That is exactly what I was unclear about.

TO summarize what I 'think' I have gathered from your reply.... in my crude drawing below......



A break in the neutral at the yellow X, will NOT send unbalanced 240 over L1 and L2 unless there was a load at outlet 1 (prior to break).

Remove outlet #1 from equation completely... breaking the neutral now... both L1 and L2 circuits would be dead, not turn them into a 240 ciruit together.

THat is why we pigtail that outlet #1.... and even if that pigtail connetion failed (say the X break is the pigtail), then both L1 and L2 circuits would be dead (no overvoltage situation).

Thanks for your patience with me... let me know if my reasoning is correct.

Happy Thanksgiving.
Opening the neutral at the yellow x WILL cause an imbalance, but only to the loads to the left of it.
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Old 11-24-2013, 01:39 PM   #26
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Ahhh...you beat me to a diagram.

This image isn't near as nice as my horsey pictures but it may help. The blue things are supposed to be resistors (loads in the outlets) or even springs if you want to look at it in a mechanical sense.

Depending on how many loads (or springs) that are on each phase, it can make the neutral float anywhere in between the two phases which gives you the overvoltage/undervoltage problem between the neutral and each phase.

If the loads (springs) were perfectly matched between phases the neutral would stay in the center and you would never know that there is a problem even though the neutral is open.

basic outlets on MWBC question-broken-neutral-modified.jpg

Last edited by 8V71; 11-24-2013 at 02:09 PM. Reason: making corrections
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Old 11-24-2013, 01:43 PM   #27
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I'm getting confused now. I think I have been giving you wrong information.

Edit: No, I'm sorry everything is back on track. Like 480 said, there will be an unbalanced situation with the yellow X broken. I also took a sentence out of my diagram that was incorrect.

Last edited by 8V71; 11-24-2013 at 02:13 PM.
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Old 11-24-2013, 01:50 PM   #28
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Old 11-24-2013, 02:05 PM   #29
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Opening the neutral at the yellow x WILL cause an imbalance, but only to the loads to the left of it.
Then my reasoning failed.

If you break the neutral at the X in my diagram, then all outlets (ABC) on L1 and L2 will see the unbalanced 240 depending on loads.

Everything relies on the integrity of the pigtail connection at outlet 1.

If you opened the neutral at X with power off to only one leg then the other leg would be dead, not a complete circuit. If open the neutral at x with power on to both legs, then you will get the over/under voltage situation on both L1 and L2.

If your still reading... I apologize for the jumble.
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Old 11-24-2013, 02:32 PM   #30
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Just think of it as an MLM. You do something wrong it F's everyone in your upline not your downline
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Old 11-24-2013, 02:33 PM   #31
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Just think of it as an MLM. You do something wrong it F's everyone in your upline not your downline
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Old 11-24-2013, 02:41 PM   #32
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Then my reasoning failed.

If you break the neutral at the X in my diagram, then all outlets (ABC) on L1 and L2 will see the unbalanced 240 depending on loads.

Everything relies on the integrity of the pigtail connection at outlet 1.

If you opened the neutral at X with power off to only one leg then the other leg would be dead, not a complete circuit. If open the neutral at x with power on to both legs, then you will get the over/under voltage situation on both L1 and L2.

If your still reading... I apologize for the jumble.
My fault, I gave you wrong information in post 23. It should be correct now.
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Old 11-24-2013, 04:28 PM   #33
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I understand completely now....

Was it ever an acceptable practice to use a device to feed the neutrals thru?

When did the current pigtail rule come into effect?

Is it common to see an outlet wired this way in the field / on service calls?

Last edited by soe; 11-25-2013 at 09:30 AM.
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Old 11-24-2013, 07:05 PM   #34
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Originally Posted by drumnut08 View Post
. Yes , because you're not counting on the continuity of the device as a feed through . It's an unbroken conductor and the circuit integrity I still intact on device replacement , or that's what I think anyway , lol ?
Until an idiot cuts the old device from the box and uses just wraps the wires on the new device. I loop em right thru, it's a time saving thing.
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