Big Voltage Drop Under Load

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redhorserider

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I encountered a strange problem today. When I turned on a Cadet Heater, the surrounding lights either got brighter or dimmer. At the panel, I checked voltages -- and sure enough, the circuits on the same phase as the heater now read 86 volts to ground, while the other phase read 165 volts to ground. When I turned on another heater, different phase, all returned to a normal 122 volts to ground. This is a single phase, residential system. Since there was no ground rod (!!), I installed 2 ground rods, but it still has the problem. The voltage doesn't float, but its almost as if something is wired in series? Any ideas?
 
loose neutral...in the panel, the meter, weatherhead or on the poco side....send me a check for $165, that's our diagnostic fee....
 
Yes.
You should be able to manipulate the voltages on each side by turning heavy loads on and off.

The loose terminal should be hot and have excessive voltage drop across it under load.
 
To emahler:

To emahler:

The check's in the mail . . . if you find the loose connection!!

Thanks I'll keep checking the neutral connections back to the transformer.
 
Hate to harp on it, but..check the crimp on the drop. If you have problems at the panel then it is before there. If it's not an aireal (spelling?)drop then you may have a wire burnt in the ground. If it aluminum wire then you can bet on it.
 
If things don't make sense, it means you are assuming something which is not true. In this case, I'd say it is your mental image of how this place is wired.

I would guess somewhere upstream there is a center-tapped 240v transformer supplying the house. There is maybe up to one ohm in series with this center tap, so that a heavy 120v load on one side drops its voltage, while boosting the voltage to the other side [because the total must stay at 240v]. The boosted side will be burning out light bulbs.

A house inspector left my house in this condition. I got home, turned on the lights, and when I turned on the cooktop the lights went crazy.

Loose neutral connection at the panel.
Found it with a voltmeter.
Tightened it.
Problem gone.
It may have been a coincidence that this showed up after the inspector was here.
 
redhorserider said:
Wouldn't the new ground I established via the ground rod stabilize the voltage?
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No, not in the least. (OK maybe a very small amount)

I agree with the others, look for a neutral connection in bad shape.
 
correction

correction

This was a lot harder to figure out than I remember it to be.

With 10 ohms in series with the center tap due to loose connections or corrosion, with a 15 ohm load on one side and a 25 ohm load on the other,
the 15 ohm load should see 105 v and the other one should see 135 v. They'll be 1.6 amps (the difference between the 15 ohm load current and the 25 ohm load current) flowing through the neutral, so 16 watts is dissipated in this bad connection.
 
redhorserider said:
Wouldn't the new ground I established via the ground rod stabilize the voltage?
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No, you need a metallic connection between the panel neutral and the utility transformer neutral.
 
I have seen instances where the concentric neutral conductor inside of the service cable was completely inhert. :-?

Nothing to do but replace the entire service drop in that case.

SO, if all the connections check out, check for cable integrity. ;)
 
Mkay...what sort of service is this. Underground/overhead/apartment or multi family like a quad. About the center tapped xfmr...wouldn't the NG bond at the service entance stop the float? Please... this is for posterity...namely my own.:)
 
redhorserider said:
Any ideas?
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Yep, listen to what everyone is telling you! You have a neutral problem (actually, it is probably the serving electric utility that has an ACSR neutral in their service drop that has come apart due to corrosion and age). Instead of spending a boatload of time on the problem, call the serving electric utility and let them tell you that it is your problem if it is not theirs. The odds are that it is their service drop.

For those who don't know, ACSR is Aluminum Conductor, Steel Reinforced. This is a great conductor in larger sizes but has a problem in smaller sizes. The smaller 7 strand conductors are 6 aluminum strands around a center galvanized steel strand. This gives a lot of strength to the conductor but dissimilar metals act as a battery when wet and corrosion develops over the years.
 
Also known to us laymen as the 'crimp' on the drop. I had on slip whil I was tempin' it back to the building after a storm. Knocked me off the roof and into the azaelas. If it's underground they almost always aluminum. One slight knick and the wire will eat itself in two.
 
redhorserider said:
Wouldn't the new ground I established via the ground rod stabilize the voltage?
Click to expand...

redhorserider,

The electrode is mainly for lightning protection but also for any other over-voltages, it is not supposed to be use as the primary return path but it may contribute. Because of this the electrode is not needed for circuitry to function but the service grounded conductor is. Check out Grounding & Bonding: The Big Picture Post, this is a great explanation for grounding & bonding.
 
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what would make you think that driving an additional ground rod would make a differnce in voltage? this is a pretty basic level trouble shooting problem, do you work in the electrical field?
 
Willie Pete said:
Does anyone know if you can drop two sizes on the neutral in residential service conductors?
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No problem, the service drop and service laterals are in the purview of the serving electric utility most of the time. The NESC covers those installations if they are owned by the serving electric utility. :)
 
Willie Pete said:
Does anyone know if you can drop two sizes on the neutral in residential service conductors?
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If you are discussing service entrance conductors, the neutral may be sized in accordance with 220.61 and be reduced a bunch. When I was doing contracting work in the dark ages, I had an installation where I had a 4 AWG Cu 75?C neutral and 3/0 Cu 75?C conductors for a total electric home. All of the heat and the WH put no load on the neutral so the neutral calculated to be about 50 or 60 amperes (I no longer remember the exact calculations). I know the service calculated to a skosh (technical term) over 150 amperes. I had to size the neutral for the minimum permitted by Table 250-94 (Table 250.56 now). :smile:
 
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