What happens when electric neutral cut/disconnected? (2025 Update)

I don't believe I've ever seen an open neutral on a service, where the ground was able to carry the load, although if it did carry the load, noone would notice, and I wouldn't get involved. Typically you have lighting and appliance imbalances, which tip off the property owner to the problem

Two 120V circuits turn into a single 240V series circuit, that's what happens. This is very, very, bad, as it tends to let the magic smoke out of everything on those circuits.

Nope.

Not unless there's a ground fault.

No.

Back in the olden days when all the homes were connected tgether by a solid metal piping systen, nothing would happen. Now days you would end up with an unbalanced service. One side opf the panel would have high voltage and the other would be proportionately low. Dirt is a terrible conductor and your ground rod is pretty useless as a neutral.

The neutral conductor is the return path for the current back to the transformer. If the transformer as well as the home had a good grounding system and soil conditions were right, current would flow through the earth to the transformer.

If there was not an ideal grounding system in place you could possibly have

The electrical code does not require that your grounding electrode conductor be the same size as your neutral conductor, which incidentally is normally smaller than your hot conductors.

Well any one circuit could have normal voltage or have anything between 0 and 240 volts. I used to work for a photo studio that was in it's second location. The first one burned up due to this little problem. The second one also suffered from it on the first floor. The basement (processing and finishing area where I spent most of my time, was OK.

Under this conditions you can turn on one light and others may become brighter or dimmer or some of each. You really don't want this to happen.

Note. Having a good ground will not help, unless that ground is also having problems.

I can answer this with experience. A long long time ago, (about 1987) we experience some weird happenings with our lights and whole house fan. The whole house fan is what tipped us off to the problem initially. It all of a sudden just slowed down. Some lights were bright, some were dim. The TV would not come on. After poking around a bit, i got out the (analog) meter and found some outlets had about 80 volts and others had about 144. Then, some how, i had the brilliant idea of turning on the oven. When i turned the oven on, the fan went back to normal, the lights normal. The 240v load apparently balanced the system. I was at somewhat of a loss at that point. I was not near as experience in electrical things at that time. I called an electrician friend of mine, he came down, poked around in the box some and decided to loosen the ground on the buss. "OH! GUESS WHAT? Fire on the ground" he said. I'm like "what's that mean"?. He said "well even though i've never seen this before, it sure looks like an open neutral. So i get on the horn with the power company. FYI, it was Kansas City Power and Light. They come out, and basically look at what i'm experiencing and the first thing the guy does is pull the meter. Then he measures the voltages on the incoming legs. All is equal. Then he tells me the problem must be on the inside. Puts the meter back in and the imbalance returns. "yep , he says, problem is on your side". So at this point, i'm at wits end, not knowing what to do, so I calls the fire dept and they say 'do you have a fire'? I says no, but I will, if someone does not fix this power imbalance. So that prompts a little higher level of action from KCPL, and they come out again. The service guy makes all his checks and then talks on the radio for a while. His supervisor says "you know that sounds like an open neutral". The guy comes back and says they suspect an open neutral. At that point, I explode. I said "NO S*IT SHERLOCK" I told you guys that 3 hours ago. They ran a bare wire from my meter can to the service box on the street and lo and behold, all becomes normal again. (did i mention i have underground service?) They came out the next day and started digging. About a foot from my water meter, at a depth of about 16" the neutral wire was corroded clean in half. Apparently it had been nicked by the backhoe putting in the water line 10 year prior. Well anyway, they fixed the wire, and all was good for exactly a year to the day. It was so weird, one year later, HALF the stuff in the house quit working. I had a dead leg. When they came out, i explained what had happened the year before and so they dug again. Sure enough, about 2 feet from the neutral problem, one of the hot legs had corroded in half.

Well anyway, that's my long and drawn out story of an open neutral. I forgot to mention, I took all the documents from the open neutral service down to the KCPL office in downtown KC, Missouri and collected a check for one TV and 2 VCRs. They were fried.

steve barker

"Bill" snipped-for-privacy@yahoo.com wrote in message news: snipped-for-privacy@mid.individual.net...

If flipping stuff on causes other stuff to blow. I would quit flipping stuff on. :)

------------------------------------- Obviously an earth ground is not as conductive as a neutral wire. But it does not have to be in most cases.

In a three wire (bi-phase) service, must current entering on one hot wire leaves on the other. Only current that flows in a neutral is due to imbalance in the load.

A safety ground is not as conductive as the neutral. But it should be conductive enough so that current does not use other paths. For example, in one house, the earth ground was completely missing. A neutral wire broke inside the street transformer. So current took a return path via the gas meter. When insulators finally broke down, the house exploded.

Homeowner knowledge is quite simple to avert such failures. If incandescent bulbs change intensity when major appliance power cycle, then get the problem eliminates. In most cases, that light intensity change is a minor problem. In some cases, it indicates a threat to human life. At no time should lights change intensity due to appliance power cycling. Never ignore the symptom because in rare cases it could be a major human safety threat such as failed neutral.

How did it find that path? There has to be a connection somewhere that should NOT be there. If the neutral is broken the current does NOT automatically go to the earth ground unless there is an improper connection as these are supposed to be isolated. In a stove the 240 elements will continue to function as long as there are no controls that require 120 as these will all be shut down. That is, a computer controlled stove will cease to function, but an old fashioned stove with simple controls will still cook and heat as they use only the opposing hot legs. The neutral is only used where 120 is required.

There is often a slight momentary dimming at the moment of startup of a refrigerator compressor or central air compressor.

I would guess that what he means is that:

A - there was no proper earth ground to the panel and

B - the gas meter was bonded to the ground system of the house which is connected to the neutral at the main panel.

Exactly what I was thinking too. I've seen new construction in $1 mil homes where a similar motor load will cause lights to dim momentarily at the end of long runs. For example, turning on a shop vac. I've seen that happen in many homes. If the standard was no noticeable change in intensity ever, you'd probably need to rewire most of the homes in the US.

ITYM "lights on a different circuit than the appliance." I can't remember living anywhere where a light on the same circuit as a microwave for instance wouldn't dim even on a 12AWG, 20A ckt.

nate

Neutral and earth are bonded together @ main panel. So they are not isolated.

nate

But the earth rod and the transformer ground are not going to carry enough current to stabilize the load. Loss of neutral between the house and the service will result in the potential between the two hots and neutral varying depending on the total load on each side. So it will be divided just like it is now but not always equally. And this will affect just about everything in the house as even many 240v appliances use 120 for some things.

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Variation is minimized so that neutral currents do not use other paths (ie water heater, furnace) to obtain earth via gas pipes. So that higher voltages do not exist and did not compromise gas line gaskets.

Among many functions of earth ground is to reduce voltages due to a neutral failure. Had that homeowner reacted properly when lights were changing intensity (when 120 volt appliances were power cycling). Or had that homeowner inspected his earth grounds, then his house would not have exploded.

True. (although I've never seen a "transformer ground" - are houses now getting four wire service entrances?) My point was, though, that they are bonded together, so if the ground connection is completely lost, that unbalanced neutral current will try to find any path it can to ground, which will likely be either a water or gas line (or both)

nate

te:

Transformers are usually grounded. Houses still have 3 wires. 2 hots and a grounded neutral.

And exactly where was this home that exploded anyway?

The REAL indicator of a failed/failing neutral is lights that "flare" when a load cuts in, because the heavy load (frdge starting, etc) causes a low resistance on the one leg, causing voltage to go up on the other leg.

Cite a source that agrees It is not an intended function of earthing because it is not reliable.

As usual from homeownershub, this question was answered almost 3 years ago.

Among the answers - from gfretwell: "Back in the olden days when all the homes were connected together by a solid metal piping system, nothing would happen. Now days you would end up with an unbalanced service. One side of the panel would have high voltage and the other would be proportionately low. Dirt is a terrible conductor and your ground rod is pretty useless as a neutral."

(Unfortunately that wouldn't work for westom because he says that a metal water pipe can't be used as an earthing electrode.)

There is probably about a post a year here of bright/dim lamps caused by a bad service neutral.