Odd line voltage

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Odd line voltage Empty Odd line voltage

Post by terrydec on Fri Feb 08, 2013 5:09 pm

I've been repairing a few receivers lately so I built a little test station. It has an audio generator input, dual scope outputs and a pair of connections for a couple of ACVOM's to check the output voltage into a pair of load resistors for the wattage. I've been using a Triplett 60-NA FETVOM and a Heathkit IM-11. Since the two don't have the same scale they don't track the same and I have to figure the difference. So I bought another IM-11 online. (Of course they don't track exactly together either so some afternoon I'll have to go through and calibrate both of them.)

Now here's where it gets weird. I put each one on my variable transformer and at my mark for 117AC, which I've calibrated, and each meter scale on 150VAC they went up about half way. So I reached over and grabbed my trusty Triplett and a "widow maker". (For those who don't know a widow maker is a line cord with a plug on one end and a pair of alligator clips on the other. If you aren't careful your widow gets the insurance). It registered 90VAC. So I set down my coffee cup, got my digital meter out of the drawer and started doing some checking. EVERY outlet in my house, even one on it's own breaker, is 90VAC. That seems abnormal in anybody's book. And using Ohm's law, if my appliances are getting a voltage about 20 volts low then my current is up and my meter reading is skewed.
At least that's how it seems to me. I'm wondering if it's worth calling the electric company to ask for a line check.

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Post by Guest on Fri Feb 08, 2013 5:53 pm

Definitely. If they say it's normal, it looks like your'e up for another date with the landlord.

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Post by terrydec on Sat Feb 09, 2013 12:18 am

I think that my life is being controlled by aliens.
About an hour after I posted this, as I was cleaning up after dinner and getting ready to go out, I happened to stick the probes of the digital meter in an outlet. The meter read 121.2!
I just probed the outlet I'm using at this computer and it is the same.

(When I was born a gypsy said, "May he have an interesting life". Little did I know that it was both a blessing and a curse.)
Pretty weird, huh?
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Post by N7ZAL on Sat Feb 09, 2013 1:04 am

Your line voltage can vary with a load, so maybe a refrigerator was on when it read low? Any other load possibilities in the structure? The voltage shouldn't drop that much but maybe you are looking at some electrical wiring problems.
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Post by willy3486 on Sat Feb 09, 2013 9:12 am

One time years ago on the job I had a computer server I has having trouble with. I also had trouble with the network hubs going out. I had the installer check it and he found nothing abnormal. I even had a rep from a IBM dealer to come out and nothing. The setup just did not work properly,I even lost the power supply in the server.

I brought my meter out one day and put it in the plug the server was plugged into. When a blower motor kicked in for the AC unit I noticed the meter drop to about 90 then jump to about 150 then go back to 120. It seems the people who wired the school building wired that closets plug into the circuit the AC unit was on. I had maintainence to wire a new circuit directly for the server and no more issues.

When I was a kid my dad had a 220 volt planer a seperate panel was added for. I don't know why it did this but when the power to the planer being pulled was more than the rest of the house the meter would slow down and run backwards. Then if the AC kicked in or the planer was shut off the meter would slow down that direction then run the proper direction. They replaced the meter and it never did it again.
So other things like AC units, refrigerators,etc can cause weird issues.

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Post by Resistance is Futile on Sat Feb 09, 2013 1:51 pm

If you have bad connections (loose) and corrosion and a heater kicks in the voltage will drop too.
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Post by DancingBear on Sat Feb 09, 2013 2:25 pm

Don't forget the possibility that you may have a corroded ckt breaker in the fuse box.
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Post by terrydec on Sat Feb 09, 2013 5:00 pm

DancingBear wrote:Don't forget the possibility that you may have a corroded ckt breaker in the fuse box.
Tony

Yeah, I'm going to pop the front of the breaker box and check it out.

Interesting story. Last week a friend asked me to check out someone's outlets because they'd been having problems with their appliances. I put my LED tester in a couple of outlets and everything looked good. So I went out to the breaker box. I have NEVER seen anything worse. The main buss bars on each leg were rusted, the return buss was almost entirely green with corrosion, one leg of the primary feed was corroded and two breakers were just barely hanging. I stepped back and told them to call a licensed electrician IMMEDIATELY because the box was literally a fire hazard. Scary.
I saw the box later because my friend was going to recycle it. It was even worse than I thought. The fact that these people had any electricity was a minor miracle.
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Post by harold wright on Sun Feb 10, 2013 1:13 pm

Some years ago a friend had a lightning strike wipe out most of his service entrance ckt. breakers. After they were replaced he noted very high elec. bills/KW Hours used. Everything looked and tested normal with voltmeters. Finally someone took a really good look at the insulation on back of the metal box and it looked suspicious. So, they disconn. the input mains, opened all the ckt. breakers, and measured resistance to ground on both busses--there was leakage. The lightning had carbonized the insulating material enough that there was significant current drain from both service input 120V lines with every appliance in house off. A new service ent. ckt. breaker panel cured problem.

Harold

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Post by terrydec on Sun Feb 10, 2013 1:59 pm

Something most people don't realize is that if a breaker 'pops' several times a carbon deposit can build up across the contacts and form a resistor. Ohms law dictates that if the voltage remains the same and the resistance goes up, so does the current. I've run across this and the only sure test is to replace the breaker. Also some wires can corrode under the screw terminal, or the terminal itself can be compromised and can't be seen.

Normally I use a 'loop' or clamp type VOM to check for current. Of course these aren't very accurate. I have another 'spring' type tester for voltage. I put the leads across the line and the indicator retracts down to a green line for 115 VAC or a red line for220 VAC. I also have a 3 LED outlet tester. When plugged into a socket it tells me if the circuit is okay, reversed or not grounded. This have been an invaluable tool. It instantly identifies a problem in the wiring at the outlet or breaker box.
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Post by sparkgap on Sun Feb 10, 2013 2:32 pm

terrydec wrote:Ohms law dictates that if the voltage remains the same and the resistance goes up, so does the current.

I=E/R. If R increases I decreases.

T.

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Post by Guest on Sun Feb 10, 2013 4:10 pm

The one that I have had to deal with is with outlets that have say, kitchen appliances or other high current applications. The terminals will develop some heat and cause thermal creep to back out the terminal screws slightly and create a fault condition. I used to live in rental properties and one had voltage that would dip all the time. I checked the panel. It used the screw in fuses and half of them had coins "fused" in them. I told the landlord it was the panel or me. I hope it didn't catch fire for the next tenant.

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Post by terrydec on Sun Feb 10, 2013 4:38 pm

sparkgap wrote:
terrydec wrote:Ohms law dictates that if the voltage remains the same and the resistance goes up, so does the current.

I=E/R. If R increases I decreases.

T.
Right
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Post by terrydec on Sun Feb 10, 2013 4:57 pm

The last apartment I lived in was a converted single family building. It had a lot of tube and knob wiring and different floors were on the same loop. If someone in apartment #1 was using an air conditioner and someone else started using a vacuum cleaner then a breaker would pop.

My landlord was cheap and he had hired some goober to do electrical work in a sub panel. I asked him which wire was hot. He said white. That's when I started doing all of his work. I still do. He's the one who had me check out that defective panel.

I rewired a panel for him that had been in a flood. Of course a licensed electrician had to sign off on the job. Every wire was dressed properly and the panel had all of the circuits labeled. He was very impressed.

(Gee, we've been posting all this time and nobody has mentioned the dreaded "G" word!) Twisted Evil

P.S. Don't!
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Post by terrydec on Sun Feb 10, 2013 5:18 pm

terrydec wrote:
sparkgap wrote:
terrydec wrote:Ohms law dictates that if the voltage remains the same and the resistance goes up, so does the current.

I=E/R. If R increases I decreases.

T.
Right

I always get that wrong but it's what I meant. If the current from the breaker decreases, say from 15 amp to 14.75 amp, then it would begin tripping with less load, like a refrigerator compressor. Someone might mistakenly think that the appliance is the problem when actually the problem is 'hidden' in the panel.
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