Possible loose neutral?

[NSM]

Perhaps you have a grow op next door!

N

[daestrom]

Ditto.

After a truck knocked a ground installed 240/120 transformer for my neighbor and my house, I was having trouble with lights getting bright when the furnace started. Called the utility right away, explained that they had just re-set the transformer the night before, and what my lights were doing.

Service man showed up within the hour. Cut seal on meter and read voltages there. Had me just turn on the coffee pot. That load was enough imbalance that he could see there was a problem (and that it was on the utility side of the service). Whole line-crew showed up within the next hour and found the problem. A loose neutral when they re-installed the xfmr.

While talking with the guys, mentioned that it was real nice of them to come out after 6:00 PM and all, but it could have waited. They replied that faulty wiring on their side is a big liability issue and they had to get to it ASAP. In the end, didn't cost me a dime.

daestrom

[w_tom]

[Jim Adney]

That was the right way to take the measurements, and you've done the right thing in calling the utility. Your problem could be in the meter box or at the pole, but either way, they are the right ones to fix it.

-

----------------------------------------------- Jim Adney [e-mail] Madison, WI 53711 USA

-----------------------------------------------

[mroberds]

Short version: Utility claims they fixed something and the test results are better (3.1 V difference as opposed to 9.4 V), but I'm still not sure what exactly they fixed.

Long version:

I called the utility on Monday afternoon about 2 PM, then hung around the house, hoping to catch the lineman and hear what he found, if anything. The utility did try to call at 7:03 PM per the Caller ID. I was in another room and the machine picked up before I did; I stopped the machine and picked up and got silence. By 9 PM I hadn't heard anything, hadn't noticed the lights going out, and I hadn't retested, so I decided to call again today (Tuesday).

I called today at about 2 PM and the call center rep said that they came out yesterday and "repaired a connection at the weatherhead". To me, the "weatherhead" is the thing at the top of the conduit running up from my meter, where the wires make almost a 180 degree turn and go out through a plastic disc with holes in it. I went out and looked at it from the ground and couldn't see anything different. I can't see my connections at the pole very well, so I'm not sure if anything changed there.

I decided to retest. I measured again at the breaker panel, with most of the loads in the house shut off except as noted. The results were:

A/C uWave left right l-r notes off off 120.4 118.7 1.7 run 1 off on 120.9 117.8 3.1 on off 118.7 118.2 0.5 on on 119.0 117.1 1.9

off off 121.2 119.7 1.5 run 2 off on 121.5 119.0 2.5 on off 119.5 119.5 0.0 on on 120.0 118.2 1.8

The 3.1 volt spread does seem to be an improvement from the previous result, which was a 13.1 volt spread (-3.7 to +9.4).

I climbed up on the roof and inspected the connections at the top of the meter conduit. I have an insulated crimp splice on each hot wire, and a bare crimp splice on the neutral wire. I'm pretty sure that the hot wire splices weren't changed, as each one has a small crack in the insulation that has been there for a while, and I'm assuming the lineman would have replaced the insulation sleeve if he installed a new connector. I am not sure if the bare neutral splice was changed; even though I haven't inspected it carefully in the past, it doesn't _look_ brand new - there are some black spots (oxidation?) on it, and the engraved markings are easy to read because dirt seems to have accumulated in the grooves. There weren't any telltale bits of wire lying on the roof or shiny places on the wire next to the connector, either. The thing that holds the mechanical tension on the bare netural wire (basically a ramp on the wire and a mating ramp with a metal loop around the conduit) hasn't been changed.

I'm also pretty sure that they didn't do anything to the meter. First, my lights didn't go out. Also, even though I didn't write down the serial number on the meter seal before I called, it's at least the same type of seal, and the metal loop through the meter can tab isn't shiny as I would expect with a new seal.

It's entirely possible that the bad connection was at the pole and I'm mistaken about where the "weatherhead" is, or that the path from the lineman to the call center four states away is lossy and noisy. I'm curious to know what exactly was repaired, but the test results seem to show an improvement, so maybe I should just be happy.

Thanks to all for the advice and assistance!

Matt Roberds

[mroberds]

You know, I thought something was up when the local lighting supply house dropped off two cases of mercury-vapor bulbs over there a couple of weeks ago. I went over to ask my neighbor about it, maybe even work out a deal like a quarter ounce per volt, but he was bogarting it so I called the cops.

:)

Matt Roberds

[Charles Perry]

That would be it.

You don't look at the spread as much as the change in voltage when a single phase load is turned on verses when it is off. If the AC is 240 V, it really matters little if it is on or off.

The voltages look perfectly normal now.

Probably recrimped the neutral connector.

New seals need not be shiny. They sit in a bin in the toolbox of a truck for months or years before installation. Also, he could open your meterbase, tighten the connections, and close the meterbase without ever interrupting your power, unless you have a 60amp meter base.

Charles Perry P.E.

[SQLit]

No your not mistaken on what the weather head is.

I once had a bastard open delta service (commercial service) that lost a leg. It was dam near mid night before the line man showed. He got out of the truck with an attitude and was going to teach me something RIGHT NOW. He started spewing out the right way of testing the system as I kept my temper and held my tongue. He got the same readings as I had. Lost a phase. Then I turned on the 8 inch spot light on the roof of my service van. The light went to the transformer with one of the feeders hanging down cause the terminal on the transformer was gone. Absolute silence from the line man. They had to replace the transformer. Be happy that there is an improvement. Doubtful you will know the truth to what they really did. Never got so much as a oops from him.

[w_tom]

[NSM]

Yup.

N

[Chris Lewis]

You did exactly the right things.

For future reference: power codes require that the voltage varies no more than approximately 3-5% from a nominal 240V at the panel under worst-case conditions (ie: max power on one leg, zero on the other). Another 3-5% are permitted at the end of the circuits.

[Precise values of permitted variance will change from jurisdiction to jurisdiction.] [Note all of the below is assuming you're measuring the voltages on the main bus bars. If you're measuring at a circuit-end, double them.]

What that means, for example, is that the leg voltage at the panel on a given leg should drop no more than 4-5 volts even when max power on that leg, and zero load on the other. Given resistance in the neutral, _half_ of that would be the neutral "going towards" the maxed out leg, and half of that would be the maxed out leg "going towards" neutral.

In otherwords, (100A panel right?), drawing 100A on one leg, zero on the other, the fully loaded side could drop as much as 4-5 volts (hot-neutral), leg-to-leg drop by as much as 2-3V, and unloaded side to neutral voltage could _rise_ as much as 2-3V.

If the neutral-leg voltage varies more than half of the leg-to-leg does (see (1) below), you have a loose neutral.

All that said, there are several caveats:

1) Extreme caution should be taken when taking the voltage levels off your voltmeter. There are a number of ways they can misread, and many voltmeters are simply not that accurate at measuring RMS volts. So, don't take a few volts either way seriously.

2) While voltmeters can be fooled by back EMI (line noise), for the most part it will be minor. To minimize these affects, use resistive loads (rather than motor or electronic). Ie: heaters.

3) While it may seem that you were approximately "on" those numbers, remember that your test loads were MUCH less than 100A, so the problem you were seeing was much worse than the allowable variance. Frankly, if your wiring was good, given the loads you were able to test with, I'd expect the voltage variation to be a volt at most, but, generally speaking, you can't rely on your voltmeter to that high a degree of accuracy. Most times the variation will be extremely obvious. You were on the low side of "obvious" [+]

While your "fixed state" is _still_ outside of what I suggested above, it's a considerable improvement over what it was, and I'd be doubtful of taking it too seriously. That said, keep an eye on it.

[+] The high side of obvious is having a lightbulb on one leg expire with a BRIGHT flash when you try to turn on something on the other leg - and that "something" doesn't work.

[Dimitrios Tzortzakakis]

I'd recommend, you don't use a UPS, it's useless and a pain in the ass.One friend of mine who runs a computer shop, told me that a customer had a kaputt ups after a power outage.When the power came back, the UPS went poof.All modern hard discs have an auto parking function in case of power failure, I think, and one should save everything regularly, I think.

-- Tzortzakakis Dimitrios major in electrical engineering, freelance electrician FH von Iraklion-Kreta, freiberuflicher Elektriker dimtzort AT otenet DOT gr Ï Ýãñáøå óôï ìÞíõìá news:Xiroe.12325$Wr.100@fed1read04...