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
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
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