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Is it true that common neutral wiring will not trip breakers on overload?

Is it true that common neutral wiring will not trip breakers on overload?

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  #1  
Old 07-30-13, 10:35 PM
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Is it true that common neutral wiring will not trip breakers on overload?

I recently read that "common neutral wiring between circuits will not trip the breakers". Is this true? And, does anyone know what they mean when they refer to "wiring between circuits"? I am assuming their reference to "common neutral wiring" was to the pig-tail method as espoused by electricians like Rex Cauldwell.

Thanks in advance,
Jeff
 
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Old 07-30-13, 10:47 PM
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"common neutral wiring between circuits will not trip the breakers"
Breakers are tripped by a short between the grounded and ungrounded conductor. I don't have a clue what they are talking about. Pigtailing is a reliable and safe method that has no effect on a breaker tripping. In fact it is required in certain cases such as a multiwire circuit.
 
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Old 07-30-13, 11:08 PM
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Welcome to the forums!

No, I have no idea what someone would mean by "common neutral wiring between circuits." If they're referring to shared neutrals, multiwire branch circuits, which share a grounded, or neutral, conductor, have been successfully tripping breakers, or blowing fuses, for decades.

This might become clearer with more context. Can you quote the piece where you found this statement?

I am assuming their reference to "common neutral wiring" was to the pig-tail method as espoused by electricians like Rex Cauldwell.
What would that be? A pigtail is a 6" - 8" piece of wire used to connect a device or box to a set of conductors with the same potential which are spliced together. It has nothing to do with connections between circuits. All of the conductors are part of one circuit unless they are the neutral conductors for a MWBC.

Is that what Rex Cauldwell is espousing?
 
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Old 07-31-13, 02:27 AM
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The breaker will only see the current flowing on the hot conductors. If you are talking about a MWBC that is improperly wired, the neutral could have up to 2x the current flowing on it and the breaker will not trip.
 
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Old 07-31-13, 07:59 AM
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Okay, thank for your help! I'm not sure what a multiwire circuit is but I will look it up.

I am fairly new to wiring but have been reading Rex Cauldwell's "Wiring a House," which emphasizes the use of common neutral wiring with pig-tails as a way to keep the current from flowing through the receptacle unless an appliance is plugged in. This strategy makes a lot of sense to me.

But, since this book is not written for the beginner, I know I am missing a lot of basic information about electricity and wiring. Any recommendations on books or study guides?

This statement I read came from a book on low-EMF wiring and house building for people with chemical sensitivities. It is a self-published book and I quoted you everything that was said about the neutral wiring. Unfortunately, I can't provide anymore information. My guess is that they were referring to what Nashkat1 said:

"If they're referring to shared neutrals, multiwire branch circuits, which share a grounded, or neutral, conductor, have been successfully tripping breakers, or blowing fuses, for decades."

Thank you everyone for your help!
Jeff
 

Last edited by Jeff Huling; 07-31-13 at 08:10 AM. Reason: Thought I needed to respond to each message individually.
  #6  
Old 07-31-13, 10:31 AM
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since this book is not written for the beginner, I know I am missing a lot of basic information about electricity and wiring. Any recommendations on books or study guides?
Yes. Wiring Simplified is authoritative, in line with current code requirements, inexpensive and written for the layman. It explains both how things should be done and why that is the case. We recommend it to many DIYers just starting out, and it's not a bad reference for the rest of us. Look for it in the electrical aisle at home improvement or hardware stores, or just order it.
 
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Old 07-31-13, 04:33 PM
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emphasizes the use of common neutral wiring with pig-tails as a way to keep the current from flowing through the receptacle unless an appliance is plugged in. This strategy makes a lot of sense to me.
A minor consideration not major in most cases. Receptacles are designed to feed power to the next receptacle so much ado about almost nothing in my opinion. Again multiwire circcuits are the exception.

A multiwire circuit is both sides of the 240 to your house plus a neutral. The neutral is split and paired with each of the 240s to provide two 120 volt circuits.

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Old 07-31-13, 10:33 PM
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A minor consideration not major in most cases. Receptacles are designed to feed power to the next receptacle so much ado about almost nothing in my opinion.
YMMV, but I've had to replace receptacles several times that failed only because the circuit was continued by wiring the two feeds to the two screws for that potential.

No more for me. I only and always splice up a pigtail and terminate that to the device. Haven't had one of those fail yet, after thousands of installations.
 
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Old 08-01-13, 10:26 AM
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Originally Posted by Nashkat1
YMMV, but I've had to replace receptacles several times that failed only because the circuit was continued by wiring the two feeds to the two screws for that potential.
I'd be curious to know how they failed. Some time after installation or immediately? Body cracked as screw was tightened? Little bridge bar vaporized in use?
2 wires secured to a brass plate by 2 screws always seemed a simple fool-proof method. I always considered wire nuts to be questionable over the long haul.
 
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Old 08-01-13, 02:48 PM
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A heavy load running through a loose screw connection will heat up and arc. This can lead to a failure or a fire. Connections need to be secure in order to operate properly and safely.
 
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Old 08-01-13, 04:47 PM
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When you have the incoming line to one set of screw terminals and the outgoing line to the other set of screw terminals... there is now four places where a loose connection could happen. Any one of those screws being loose will affect that receptacle as well as every other one on the circuit after it.

If you make up splices in the junction box..... a loose screw would only affect that receptacle.
 
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Old 08-01-13, 05:51 PM
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I'd be curious to know how they failed.
The tab between the two terminal screws for the ungrounded conductors melted, on all of the ones that I remember. I don't recall seeing any other type of failure.

Some time after installation or immediately?
I don't know about all of them, of course. On the two on circuits that I'd built, they had been in service about 8 years, IIRC.

2 wires secured to a brass plate by 2 screws always seemed a simple fool-proof method.
There are two brass plates for each potential, not one, and the tab is the only connection between them.

You didn't ask, but I'll add this observation for completeness: In each case, the failure occurred on the first duplex receptacle in a daisy chain. IOW, it occurred on the tab that was carrying the full load on the circuit, with the possible exception of the load on the other receptacle on the same yoke.

I always considered wire nuts to be questionable over the long haul.
For doing what? A wire nut is as excellent device for doing what it's designed to do - protecting a well-made splice from contact with conductors and objects with a different potential. It is not a device designed for making the splice. Used properly, a wire nut will perform well.

In rehab work, I've taken apart well-twisted splices protected by the Bakelite wire nuts that were originally installed. Except for dust and a bit of surface oxidation, everything looked as good, and was performing as well, as the materials we installed as part of the upgrade or change.

There is no better mechanical and electrical connection that can be readily made between the commonly used sizes of branch circuit conductors - 10, 12 & 14 AWG - in the field than a well-made twist splice.

Originally Posted by pcboss
A heavy load running through a loose screw connection will heat up and arc. This can lead to a failure or a fire. Connections need to be secure in order to operate properly and safely.
I have no way of knowing how well the connections were made on most of the devices where this failure occurred, of course. However, two of them occurred on circuits that I installed in the house that I rehabbed while we were living in it. Those connections were made with the conductors properly stripped, curled and crimped, and with the terminal screws tightened enough to make and maintain full contact but not enough to deform the conductors. In those two cases, the failure occurred because the bridge tab failed under load.

That experience, reinforced by a chat with my friend and auto mechanic who had installed elevators in airplane hangars in an earlier life, convinced me to never trust the tabs again. In every company I worked for after re-entering the field, and on every job site I've worked on, circuit-continuation connections in device boxes have been allowed to be made by one of two methods: Back-clamping, where the device permitted that, or pigtailing and splicing. We used to set the green helpers to cutting and stripping 100 or so pigtails sometimes. We'd pre-wire 2 or 3 boxes of devices with some of those and throw a good handful of them on the cart with the devices and our tools before heading onto the floor.

No connections relying on the tab. Ever. The tab was only there to allow the two devices that shared it to be separated, as far as we were concerned.

</rant>
 
  #13  
Old 08-01-13, 05:58 PM
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Good point, PJ. Thanks. I called it quits before getting to that one.
 
  #14  
Old 08-02-13, 06:56 AM
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Never thought of it like that (melting tab). I know it's small and even has a score cut to make it break off easily but with faith in UL & mfr. testing I assumed that the tabs on a 20A recep. could handle at least 2X that current and the upstream breaker would trip long before the metal would melt. OTOH that tab could be considered a fast-acting fuse that could vaporize before the CB could react to a nasty short circuit somewhere downstream...?

I think I'll look at it differently next time I'm stuffing boxes. Not that I rely much on the double screws--the cheap "contractor grade" receps. I normally use in non-critical locations (bedrooms & such) have such flimsy plates the screws strip out.
 
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Old 08-02-13, 09:35 AM
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I assumed that the tabs on a 20A recep. could handle at least 2X that current and the upstream breaker would trip long before the metal would melt.
Some of these were 15A receptacles on 20A circuits. That should have been fine, since the 15A devices are rated for 20A pass-through, but it wasn't. They were replaced, in at least some cases, with new 15A receptacles from the 59 cent bin. The only change was the wiring method - I built a bypass with an exit ramp and connecting road for the traffic that needed to get into town.

OTOH that tab could be considered a fast-acting fuse that could vaporize before the CB could react to a nasty short circuit somewhere downstream...?
These failed from simple overload relative to what the tab could handle, from what could be observed. There was no evidence of a direct short anywhere in the string. And no, I don't think we want anyone to rely on a tab hidden in a wall box for overcurrent protection. That's what the visible, accessible and resettable breaker is for.
 
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