Floating neutral alert


#1

So having had one of these, and the consequent nasty mess it left, it strikes me that it should be really simple to spot (and since this is a Really Bad Thing it probably should alert me that I need to get it fixed pronto.


#2

This is a good idea and should definitely be easy to detect with the inputs Sense has available.


#3

Also, to be clear, the OP is talking about a compromised neutral from the home service entrance to the utility transformer MGN, also referred to as an “open neutral” or “dirty neutral”.


#4

Thanks for the clarification. There are various kinds of “open neutrals”. Sense could help detect the one you describe, but probably wouldn’t detect an “open neutral” out on a multi-wire branch circuit. Also somewhat dangerous, but mostly for your 120V devices.


#5

+1 to vote for this. Trivial to detect.

An open neutral on the main feed from the utility will at best be expensive (fried devices), and at worst end up in loss of life and property.

They are seriously no joke. Sense is in a fantastic position to help identify these conditions rapidly.

I realize that this won’t get a lot of votes since it is relatively rare and most folks don’t even know what it is, but I really hope Sense will consider making it a feature.


#6

+1000 - We lost the neutral from our utility feed from the pedestal to house early July of this year. The wire cooked underground. Seriously no fun, but Duke Energy was quick to respond. After replacing the line to my house from pedestal, the line from transformer to pedestal cooked that same day.


#7

You have my upvote for this feature request. It should be fairly easy to implement and should trigger a notification on the mobile app. Detection would be by a variation greater than a certain percentage or a certain number of volts between the voltage of the two lines.


#8

I would vote for this as well. Seems fairly easy to implement as sense already monitors the voltage on both legs of the panel.

I would have thought this was pretty uncommon, but am beginning to believe it happens more often than I would have expected.

It happened to my sister a few years ago, wire disconnected from the transformer at the pole in the middle of the night and blew out almost everything in her house.

Just yesterday a coworker asked me to help diagnose an electrical issue at his house. The lights were going crazy and he thought it was something with his solar system as he was getting high voltage. After telling him to turn of the solar he was still seeing the issue. I had him measure the voltages at his dryer plug and then contact the power company to let them know he had a bad neutral.

The power company confirmed this and since his service is buried installed a split phase transformer, at his house to solve the issue until they could fix his service. The fact they had this readily available indicates the problem occurs somewhat commonly.


#9

I agree with all the other user comments. This seems to be an easy software upgrade to make. It is one of those features that you hope you never receive an ‘alert notification’; but if you do, then you could take steps to mitigate damages.

I also encourage SENSE to graph the voltages for each leg so that we have the history recorded (not just the instantaneous readings located on the ‘Sense Monitor’ page). I would like to know when we are having a ‘brown-out’ or an ‘over-voltage’ spike.


#10

Up vote on the main topic as well as the historical voltage graph in order to keep the Utility honest.


#11

Can someone explain what a floating neutral is, how it happens, and how common it is?


#12

At the utility transformer, the input is (typically, something like) 27,000 volts. That is, volts “above ground”. It produces two “phases”, of opposite signs, based on the direction that the wires take around the transformer core. There is one set in the + direction, and one in the - direction.

Both of those output voltages are “above ground”. The high-voltage power system is “grounded” in thousands of places, at each transformer. So the +120 and -120 voltages are relative to that common ground.

There are 3 wires from the transformer to your house. +120, -120, and “neutral”. The neutral is connected to the “ground” of the high-voltage system, at that transformer.

If that “neutral” wire is loose, disconnected, or has any other mechanical problem, it is called “loose neutral”. It is loose in the sense that the voltage is not zero – it can ‘float’ to other voltages, depending on how much power is being used in the +120 and -120 circuits at that moment.

The difference between the +120 and the -120 will still be 240 volts. But, your house doesn’t know where the “0” should be. This can result in some 120-volt circuits getting 160 volts, while other 120-volt circuits get only 80 volts. The total will be 240. But it can be split anywhere in the middle. As one consequence, your plumbing or conduits can be energized.

The too-high or too-low voltages, can damage some of your 120-volt appliances. The best that can happen is that they won’t work right, or will turn themselves off. At worst, your televisions and computers might need to be replaced, or one of them might even start a fire.

How common is this? It “should” never happen. When it does happen, the power-company will dispatch a crew (immediately) to correct the problem. It is a big safety issue – so they give it high priority.


#13

@SteveHansen,

Great description. So a clear distinguishing sign of a “weak neutral” from the transformer would be mains voltages that are significantly out of balance, from one another ? Seems like that is a check that one could also do manually by looking at mains voltages ? That’s also a check that probably should be done by Sense in the setup phase, if it isn’t done already, as it could cause wildly erroneous power results.

Or are there cases where an earth ground to neutral on in the breaker box, or a earth grounded neutral coming in from the backfeed might mask the missing neutral connection to the transformer ?