My guess is that the roof was installed with out ice shield. The lower 3 or 4 feet or maybe less is susceptable(sp) to ice daming. If you get snow buildup and the heat from the house melts the snow the water will build up on the edge of the roof and freeze. It will slowly dam higher as the snow melts and will find its way into your house under the shingles. The water will come in between the wall and the outer siding or through your ceiling. The purpose for the heater wires is to provide a channel for the water drain off.
Do you also have gutters and heaters in the gutters? Usually they go hand in hand.
If someone installed them you can be sure that there is a definate problem and I would turn them on when the sun is on the roof and the snow is melting.
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