What is the purpose of the large nitrogen tanks seen by public utilities equipment?

I live in a suburb of Dallas, and by telephone poles and outdoor cable boxes, I often see a nonrefrigerated metallic, shiny gas tank about 3 or 4 feet tall, and it's labelled 'nitrogen'. What purpose does this serve?

Answer:
I asked a Verizon technician about these once, and he said that they pressurize underground cables to drive out moisture. The cables are not perfect, and will occasionally leak and allow moisture in that shorts the copper strands. Remember that the cables are often below the water table, and run under creeks, drainage ditches, etc. The nitrogen is used to dry them back out.

Liquid nitrogen is used to cool objects rapidly, to temperatures well below zero. We have a tank where I work. It is used to test electrical equipment at cold temperatures and it is much more convenient and powerful than refridgerators. For example, it can take a hot rack of equipment from 100C to -40C in , I would say, 5 to 7 minutes. No refrigerator I know of could do that.

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What is the purpose of the large nitrogen tanks seen by public utilities equipment?

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