Electrical Power Issues after Strom pulls wires from Bruce H's House
R.Kwas KA1-RBP 12/2015

Weird things happen when a neutral conductor (the normal return current path), opens.  This is well-covered on electrician Larry Dimock's excellent page here:  ( http://www.thecircuitdetective.com/mnpn.htm ).  Because his explanations and diagrams are so good, my diagrams below are inspired by those shown on his page.  

I ran across this weird and difficult-to-explain-situation (at first) at Bruce H's house several years ago now, after a storm had torn through the area and a tree had fallen, totally ripping the electrical service wiring off their house. 

The tree had torn all three service wires from the house, yet leaving the connections of two intact.  When I walked in and asked "How is your electrical system?" (figuring they would have to have SOME sort of symptoms, depending on which wire it was that was open), I was told "everything is working fine!"  I was intrigued!  I figured if it was one Phase wire that was open, only half of the 120V loads would be working, and if the Neutral wire was open, none of the 120V loads, and only the 240V loads would be working...but everything was working just dandy (and no dim/bright lights were occurring with the disconnected and imbalanced neutral either, as described on Dimock's page)...what the?...either Phase or Neutral wire open would be a break in the normal current path, so I couldn't quite explain the total lack of symptoms...since 120V loads were working fine, I knew there had to be a return neutral current path, but just where?...I needed to "think on that a bit"...I asked to see the Load Center for a closer look, knowing that something was amiss, and hoping that I would get a clue there.  While looking at the Load Center, I tried to picture the complete current path for 120V loads if the Neutral wire was open outside the house...just how was the current returning to the pole transformer Centertap if that Neutral was open???...then I saw it...the other connection to the Neutral Bar!...the connection to the water pipe was the answer! 

Since we live in the "city" and are supplied by municipal water in metal pipes, these cold water pipes are typically also used for the Safety Ground at the Neutral Bar (a grounding variation per electrical code).  As a Safety Current path only, this is not the Normal Current path, but it was indeed the current path under this fault condition...my friend's neutral current was flowing to his Neutral Bar, then going through the Municipal Water Pipe, to the neighbor's Neutral Bar, and returning to the pole Transformer Centertap by way of the neighbor's Neutral wire!  Mr. Spock might have said "fascinating" at that point, because it caused me to come to the realization that the neutral current of the house with the problem was being returned by their neighbor's Neutral wiring(!)...and so if the neighbor's wiring had a problem or was inadequate for the increased current, a problem at your house could conceivably cause a fire "next door"! 

Understanding the abnormal current path, I did advise them to only use minimum electrical loads until the wiring was repaired and back to normal, and not to use the dryer at all.  

Thankfully, no secondary disasters occurred.  The Neutral wire connection was repaired, all service wiring was reattached to Bruce's house during post-storm restoration work, and all current paths were normalized.

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Drawing 1 of a typical Residential Electrical Power Distribution. 
One Transformer supplies multiple residences (Houses 1-4) with power 120V and 240V power.  Connection details of House 2 and 3 are shown.
Each house has three wires connecting it to the Transformer...both ends of the Low Voltage Secondary winding, as well as the Centertap.

 

Diagram 2.  Normal Conditions.  
Normal current paths are shown for Houses 2 and 3 (Current paths for 1 and 4 would be similar).
For the purpose of simplicity and clarity of the diagram, only a typical 120V load current path (powered by half of the Transformer Secondary) is shown in Yellow for House 2, and only a typical 220V load current path (powered by the full Transformer Secondary) is shown is shown for House 3 in Turquoise.  Both houses could obviously have other load paths which are not shown. 

 

Diagram 3.  Failure Condition at Bruce's House (House 2). 
An open Neutral Service wire occurs, but there are NO SYMPTOMS(!), and 120V loads are all working as expected.  
Question:  How is the House 2 Neutral Current being returned to Transformer Centertap? 
Answer:
 Through the Safety Ground connection at Neutral Bar, and Municipal Water Piping!
Explanation:  House 2 Neutral Current cannot return from Neutral Bar, by way of the open Neutral Service wire (Normal Current Path), to Transformer, but since Neutral Bar of House 2 and House 3 are effectively connected together (by way of the Municipal Water Pipes, which are also used to tie the Neutral Bar to Ground), House 2 Neutral Current is conducted through an Abnormal Neutral Current Path, (the water pipes!), to Neutral Bar of House 3, then returned to Transformer Centertap by way of the Neutral wire of House 3 Service wiring (actually also by way of the service wiring of Houses 1, 3, and 4, since all of these connections are effectively in parallel back to the Transformer Centertap)...the point being, that this current, additional to these house's normal currents, might overload a marginal connection on their Neutral Current Path. 

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Reference Links:

Mr. Dimock's site is worth a visit! ( http://www.thecircuitdetective.com/index.htm )  including his examples of Ground Faults and troubleshooting:  http://www.thecircuitdetective.com/faq.htm#gf

Good general explanation of Ground Faults:  http://www.masterworksservices.com/files/GFCI_by_Sam_Goldwasser.pdf  ...although in this case, no CFI breaker tripped since all the current in the Black load circuit hot wires was returning by way of their respective White Neutral wires, because the problem was upstream of the Load Center.

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External material sources are attributed.  Otherwise, this article is Copyright © 2015.  Ronald Kwas.   The information presented comes from my own experience and carefully considered opinion, and can be used (or not!), or ridiculed and laughed at, at the readers discretion. 

You are welcome to use the information here in good health, and for your own non-commercial purposes, but if you reprint or otherwise republish this article or diagrams, you must give credit to the author and to this site as the source.  If you donít, youíre just a lazy, scum sucking plagiarist, and the Boston Globe wants you!  As always, if you can supply corrections, or additional objective information or experience, I will always consider it, and consider working it into the next revision of this article...along with likely the odd metaphor and probably wise-a** comment.