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Discussion Starter · #1 ·
Hello all:
So while working on an unrelated project near the electric meter, I accidentally bumped the meter with my elbow. Unknowingly to me, the meter box was barely attached to the wall and rocked pretty good. A few seconds later my wife comes out and says all of the power in the house is out. I then go inside and see some lights are on, and some not. Those that are on are very bright and others are dim. I also start to sense a burning smell in the kitchen, and when I went outside to check the garage, there was the same smell and light smoke visible. In a panic I run back in the house and kill the power at the panel. As things calmed down (no more smoke) and my neighbor I had contacted during all of this came over (lic elect), as well as the local electric co. crew, the meter gets pulled to reveal a corroded ugly scene. I was told that when I hit the meter I knocked loose the neutral. The smoke I smelled was the microwave oven in the kitchen and my battery charger in the garage being fried by the overvoltage. They temporary connected me until I can repair things permanently.
My question has to do with what I may expect next in regards to future issues? Did wiring in the walls get damaged? Will there be problems with appliances running on 110v power? I checked the outlets that had things plugged into them and they looked fine.
Scary time but I'm glad it happened when I was home. Now to upgrade to a new panel...

Thanks!!
 

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Apologies for possibly high-jacking this thread but I was going to start one on a similar experience that might have ended up being redundant. A while back my brother had the neutral lug on his service transformer fail (later repaired/tightened by utility). He first noticed the signs during his morning 'wake-up routine' as lights and appliances began acting strangely - smoke from a couple was his first clue. I only sort-of get the science behind the impact of an open neutral. I don't fully understand why 110v circuits over-volt, since the neutral side of the circuit is still referenced to ground (perhaps a high impedance path but still a path). Even 220v circuits, in my mind, can only achieve the voltage of the secondary windings of the transformer. Perhaps series circuits are created, or it's a more complicated application of ohm's law that I'm not getting? Not really a diy problem - just trying to become smarter. A number of appliance circuit boards and a couple lamp sockets replaced and all seems good in his house. Interestingly, 'old school' appliances with no electronics survived unscathed.
 

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Apologies for possibly high-jacking this thread but I was going to start one on a similar experience that might have ended up being redundant. A while back my brother had the neutral lug on his service transformer fail (later repaired/tightened by utility). He first noticed the signs during his morning 'wake-up routine' as lights and appliances began acting strangely - smoke from a couple was his first clue. I only sort-of get the science behind the impact of an open neutral. I don't fully understand why 110v circuits over-volt, since the neutral side of the circuit is still referenced to ground (perhaps a high impedance path but still a path). Even 220v circuits, in my mind, can only achieve the voltage of the secondary windings of the transformer. Perhaps series circuits are created, or it's a more complicated application of ohm's law that I'm not getting? Not really a diy problem - just trying to become smarter. A number of appliance circuit boards and a couple lamp sockets replaced and all seems good in his house. Interestingly, 'old school' appliances with no electronics survived unscathed.
Without a neutral connection a series parallel circuit is created (through anything connected to the home's wiring) between the two hot legs. This causes under voltage and over voltage on these devices depending on the overall impedance on this new circuit
 

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Apologies for possibly high-jacking this thread but I was going to start one on a similar experience that might have ended up being redundant. A while back my brother had the neutral lug on his service transformer fail (later repaired/tightened by utility). He first noticed the signs during his morning 'wake-up routine' as lights and appliances began acting strangely - smoke from a couple was his first clue. I only sort-of get the science behind the impact of an open neutral. I don't fully understand why 110v circuits over-volt, since the neutral side of the circuit is still referenced to ground (perhaps a high impedance path but still a path). Even 220v circuits, in my mind, can only achieve the voltage of the secondary windings of the transformer. Perhaps series circuits are created, or it's a more complicated application of ohm's law that I'm not getting? Not really a diy problem - just trying to become smarter. A number of appliance circuit boards and a couple lamp sockets replaced and all seems good in his house. Interestingly, 'old school' appliances with no electronics survived unscathed.
The connection to Earth for the Neutral is not there for that purpose and seldom to never will work as a current carrying path back to the utility transformer, except in very specific installations.
 

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I don't fully understand why 110v circuits over-volt, since the neutral side of the circuit is still referenced to ground (perhaps a high impedance path but still a path). Even 220v circuits, in my mind, can only achieve the voltage of the secondary windings of the transformer.
240V circuits are unaffected by an open neutral. Only 120V circuits are affected, and only half of them can experience overvoltage. The other half will experience a corresponding undervoltage. You pretty much answered your own question when you said, "the neutral side of the circuit is still referenced to ground (perhaps a high impedance path but still a path)." That extra impedance (the resistance of the home's grounding electrode system, plus the resistance of the earth, plus the resistance of the utility's grounding electrode system) is added in series with the neutral if the nice big fat neutral conductor is interrupted. That extra impedance is always going to be totally unreasonably high. Even an ohm or two would cause problems, and the real number will be more like tens of ohms.

It only takes some simple arithmetic to see that adding 10 ohms in series with the service neutral will cause dangerous overvoltage on half of the 120V circuits if there is any significant load imbalance. A difference of 5A between the two legs will cause one half of the panel to see 170V and the other side 70V. A 10A difference will put 220V on one side and 20V on the other! That's assuming only a 10A grounding electrode impedance, which is much lower than usual. Around here in Arizona, a pair of ground rods can often have well over 100 ohm impedance.
 

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That doesn't properly describe an open neutral. When the neutral is open the current is the SAME in both sides. The voltage shifts because the loads are different and thus the voltage drop across them divides based on the impedance. The loads are the same on both sides then the voltage drop will be equal.
 

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Simple answer: with a neutral, you have a 120v voltage drop on each side, so current is determined (approximately) by V=IR for V=120. Without a neutral, you have a 240v voltage drop across BOTH sides combined, with nothing holding the middle at 120, so you have V=I(R1+R2) for V=240.

If R1=R2, then you get a 120v voltage drop against each half. Otherwise IR1 (the voltage drop across the first load) is different than IR2 (the voltage drop across the second load), so one is getting too much voltage and one is getting too little.

R1 and R2 may each be a number of loads in parallel (i.e. each is the load of everything coming off one of your hot legs), but the effect is the same because the combined parallel load can still be modeled as one load.
 

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That doesn't properly describe an open neutral. When the neutral is open the current is the SAME in both sides. The voltage shifts because the loads are different and thus the voltage drop across them divides based on the impedance. The loads are the same on both sides then the voltage drop will be equal.
Only if the neutral is completely open, and not bonded to the grounding electrode system. The question was why the voltage imbalance would occur if the neutral is still bonded to the grounding system.
 
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I had an electrician argue with me that a neutral isn't really necessary as it doesn't carry any current. :vs_worry: I explained that in the case of a MWBC, this would only be true if the load on each leg was completely balanced. I drew a circuit similar to what Tom738 described to which the electrician dismissed as being false. I suggested that he go home, disconnect his service neutral and report back the following day with any findings.
 

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Discussion Starter · #14 ·
BigJimmy said:
I had an electrician argue with me that a neutral isn't really necessary as it doesn't carry any current. :vs_worry: I explained that in the case of a MWBC, this would only be true if the load on each leg was completely balanced. I drew a circuit similar to what Tom738 described to which the electrician dismissed as being false. I suggested that he go home, disconnect his service neutral and report back the following day with any findings.
hopefully you found a new electrician....
 

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I had an electrician argue with me that a neutral isn't really necessary as it doesn't carry any current. :vs_worry: I explained that in the case of a MWBC, this would only be true if the load on each leg was completely balanced. I drew a circuit similar to what Tom738 described to which the electrician dismissed as being false. I suggested that he go home, disconnect his service neutral and report back the following day with any findings.
That's funny; I wonder why he thinks a neutral is installed then.
 

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Discussion Starter · #17 ·
BigJimmy said:
Ha! Well, he wasn't doing work for me. Actually, he was doing lineman work here in Chicago on a project that we were both working on.
funny you said that because if it wasn't for my neighbor that identified what the problem was, the guys from the power co really had no idea what happened.
 

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Linemen aren't electricians, most know nothing about electrical theory. Power can be transmitted over a 3 phase delta configuration which requires no neutral, but single phase 240v electrical systems require a neutral.
 

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Linemen aren't electricians, most know nothing about electrical theory. Power can be transmitted over a 3 phase delta configuration which requires no neutral, but single phase 240v electrical systems require a neutral.
Actually, Lineman regularly install distribution transformers (13.8K:240 and 5.6K:240) here in Chicago neighborhoods. I hope that they know what the neutral is! :smile:
 

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I had an electrician argue with me that a neutral isn't really necessary as it doesn't carry any current. :vs_worry: I explained that in the case of a MWBC, this would only be true if the load on each leg was completely balanced. I drew a circuit similar to what Tom738 described to which the electrician dismissed as being false. I suggested that he go home, disconnect his service neutral and report back the following day with any findings.
Hah. Reminds me of a plumber who tried telling my mother that if he installed the mixing valve she wanted before the water hit the toilet (to reduce sweaty toilet problems), the toilet would explode from having the hot water mix with the cold water.
 
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