Loose neutral damage

[kwired]

@kwired
Yes, imbalance. But I mentioned that, if one load shorts itself then 240v will (might) be on the other load, and poof.

Since what, about 1980, resi panels are fairly ok being "balanced" across both lines, as the practice became better at doing things?
There's likely two scenarios to be had.
1) the resi is an electrons saver so they keep everything off, in this case using one load means it won't turn on, then they try other siwtches and stuff, nothing works, they call someone.
2) the resi has all sorts of stuff on all the time, the more stuff 'on' the lower the imbalance will be across loads (bc's) that are looping amps from one pole to the other.

And then you have that most N bars in panels are stabbed to Earth, so unless the example of issue is a fully floating N bar, there's likely still amps flowing pole to Earth. You can create a test model of this using a small low-v CT xfrmr, just tap the CT at shared load point of connection to a ground rod, then lift off the CT at xfrmr, what do you get?

The more items you have connected the more likely you can achieve some balance, doesn't matter if residential or not. Metallic water system in the neighborhood - you have a low impedance connection through other services and back to the source and could go somewhat indefinitely with a bad service neutral and never see any effects. Ground rods? most those are not low enough resistance to make all that much difference should you have a bad service neutral. In fact I've seen perfectly good condition but lengthy and undersized neutral conductor yielding results that initially make one think there is a bad neutral, and these would typically have less resistance than a ground rod probably has.

 

[jaggedben]

If a service neutral is lost, the neutral may still be grounded at the service, but if a subpanel feeder neutral is lost, it generally won't still be grounded. But high impedance grounding doesn't do very much. Imbalanced L-N voltage happens any time there's an unbalanced load. How much is an inverse function of the resistance on the neutral, and grounding electrodes have too much resistance.

 

[Frank DuVal]

Since what, about 1980, resi panels are fairly ok being "balanced" across both lines, as the practice became better at doing things?
There's likely two scenarios to be had.
1) the resi is an electrons saver so they keep everything off, in this case using one load means it won't turn on, then they try other siwtches and stuff, nothing works, they call someone.
2) the resi has all sorts of stuff on all the time, the more stuff 'on' the lower the imbalance will be across loads (bc's) that are looping amps from one pole to the other.

And then you have that most N bars in panels are stabbed to Earth, so unless the example of issue is a fully floating N bar, there's likely still amps flowing pole to Earth. You can create a test model of this using a small low-v CT xfrmr, just tap the CT at shared load point of connection to a ground rod, then lift off the CT at xfrmr, what do you get?

Please, draw the circuit. It is really simple to see how the voltage inside a residence will now be not stable at 120 volts from line to neutral when there is no neutral connection from the residence to the transformer.

The panel might be balanced as to loads that might be on, but never to loads that are always on. How would one do that as an electrician? Your always on will not match the owner's always on.

Turn on the toaster and the other side of the service now approaches 240 volts. See? Look at the diagram I suggested you draw.

Stabbing to earth provides no real current path. 25 ohms will not balance a toaster. Oh, and that is 50 ohms, if you count both the house and the pole ground rods. At best that might balance a 2 amp load.

In a neighborhood with metal gas pipe and metal water pipe that interconnects houses, then the imbalance will be less, might even be none. I've seen that also. Neutral laying on ground., house running fine. Had both gas and water metal pipe interconnecting houses, so the no neutral house was using the neighbor's neutral connection. Neutral to ground in service panel to bond of pipes to neighbor's bond of pipes to ground to neutral in service panel to power pole.

I have seen this imbalance in houses and commercial. Called the power company to fix once I determined it was not in the service panel (power company here owns meterbase wiring back to source).

One example long long ago, was back when I also repaired tube TVs. A Zenith would go to blank raster, no video. I noticed the light near the TV would be dimmer when this happed, and the lights elsewhere were brighter. Hmm, heard something about Zenith RF Oscillators not working once line voltage drops to 90 volts. YEP! Line voltage dropped to 85 volts when the furnace motor turned on. TV service call turned into electrician service call. Checked SE cable coming out of meter, pretty warm, called Vepco to fix TV issue. Ha! They were there within 30 minutes at night. Tightened neutral connections in meterbase.

 

[LarryFine]

Fiona, you're taking the 240v thing to literally. No, neither half would see 240v but an imbalance of something like 160v and 80v is easily obtainable, and the 160v can do some damage.

Line conductors carry current in an attempt to keep the load end of the circuit at the same voltage as the source end. Likewise, neutrals carry current in an attempt to keep their load end at the same zero volts to earth as the source.

We call the inability of either to do so "voltage drop". An open neutral can not maintain the voltage balance. Such a condition could cause a L-N voltage to reach total L-L voltage under unusual, but totally possible conditions.

For your reading pleasure, from a thread titled Understanding the Neutral Conductor:

Understanding the Neutral Conductor

Dennis, here's a really basic lesson, and we'll start with direct current, because the fact that we use alternating current is not relevant to the basics: Picture a battery, like you'd find two of in a flashlight. You have a terminal at each end, with a difference in potential of 1.5 volts...

forums.mikeholt.com

 

[ptonsparky]

Turns out the neutral issue was at a farm the neighbor owns. His area electrician did not delay and found the bad connection at a pole top.

The neighbor asked, my brother, if that could have been the reason he felt tingles as he walked thru the yard on occasion. Hmmm...maybe.