Dimming Lights in Barn (underground wire)

Years ago I rented a farm for one year, and the wiring to the barn was an underground triplex cable (made for underground use). The run was about 200 feet with a shed in the middle. The lights in the barn worked fine in the summer, but in winter they would always be dimming and getting brighter (very noticibly). I thought it might be the livestock heaters in their tanks to prevent the tanks from freezing. I calculated the load to be about 2000 watts spread over 4 20 amp circuits. So that should have not been excessive.
To check on this, I unplugged each heater and the heat tape on the hydrant. The only thing thrned on was the four 100 watt lightbulbs on the ceiling. The lights still went from dim to bright in the barn. I opened the breaker box in the barn and checked the connections. I even cleaned the ends of the #4 cables where they enter the breaker box, and I was sure to tighten the connectors well. I did the same with each breaker contact and tightened every #12 wire connection. The lights still did the same thing.
OK, I went to the small shed. There was only one outlet in there, and I plugged in a trouble light. That light also dimmed and brightened. That main cable came into that shed, and went to a small box with only one breaker. Again, I cleaned and tightened every connection. Still no change!!!!
I went to the house and did the same thing, cleaning each cable, tightening everything, etc. The lights in the house DID NOT have the dimming problem. The barn wires were fed off the house MAIN panel with a separate 50amp breaker feeding the barn. I then replaced that 50A breaker. Still no change!!!!
I hooked a multimeter to the house outlets and in the main panel, and to the output side of that 50A breaker, and the voltage was constant.(around 120v). Then I hooked that meter in the barn and could see the voltage drop from 120 to 110, sometimes as low as 90v. In that shed, it was the same thing, (voltage irregularity). One night the outside temperature dropped well below zero and the lights were dimming even more. Unplugging the tank heaters helped, but did not solve the problem. That same night there were more animals in the barn, and we had to install another 1000W tank heater. With that one plugged in, the lights go so dim, we could hardly see. I metered the voltage and saw it go as low as about 65 volts, and on BOTH sides of the 220 line. We literally had to use flashlights that night.
As far as I know, there were no splices undergound. It was just the 3wire #4 underground triplex (all 3 wires insulated), from the house to the shed, where they connected in that small box, and from there another run of the same cable to the barn.
We never could figure out this problem, and the landlord was unwilling to do anything about it, (and many other things), so we moved in spring.
However, I am posting this because my neighbor (where I live now), has the same problem. I was there helping him with chores and noticed his lights dimming in the barn. He said they have done that for years, but the house is OK. In his case, the wires come directly from a centrally located meter pole, and go underground to the barn. The house is fed off an overhead triplex, and the house is fine. We opened his panel and tightened all the screws, and looked for any charred wires and/or breakers. Everything looks fine. All he has is 2 lightbulbs, one 1000watt tank heater, adn one small heat tape. We shut off the heater and heat tape, and those two 100W bulbs dim and get bright. He too has #4 underground triplex. and he said he never notices this in summer.
What's the deal with this? It appears that for some reason this underground triplex does this in cold weather. I know a lot about wiring, but this makes no sense at all. The neighbor knows for sure there are no splices in that cable, and it goes right from the pole to the barn.
Any comments?????
Thanks
Mark
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On Wed, 14 Jan 2004 01:21:39 -0600, snipped-for-privacy@UNLISTED.com wrote:

You need to check the neutral connections as well as the hot ones, bad neutral can cause all sorts of interesting effects.
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- Charles
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wrote:

Like I said, I cleaned and checked ALL connections. This included the neutral.
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I can only think of 2 suggestions off the top of my head since you've checked just about everything else.
1) Call the power company and have them check their lines.
2) Have the underground wire tested for leakage to ground.
It is possible to install a transformer that will automatically compensate for the voltage fluctuations. I don't how much it would cost to do that, but you may want to contact an electrical engineer to have plans and specifications made and solicit some bids from electrical contractors. Your power company may be able to help you with this.
John Grabowski http://www.mrelectrician.tv

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One question: Is the underground feeder copper or aluminum? Direct burial aluminum wire has a history of failure if installation precautions are not strictly observed.

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