Введите силовой кабель в распределительную коробку в нижней части трубы.

Сondulet - это приспособления (опоры, контакты...) для монтажа проводки в жесткой трубе (см. Лингво). Здесь нет нужды их упоминать в переводе, поскольку "распределительная коробка" фактически предполагает их наличие.

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Note added at 2 час (2006-11-20 14:18:48 GMT)
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Сведения о Сondulet:

Cooper Crouse-Hinds Celebrates 100th Anniversary Of Its
Breakthrough Condulet Electrical Product
Cooper Crouse-Hinds® is celebrating the 100th anniversary of the introduction of Condulet® conduit fittings, a breakthrough product that solved a key problem for an industrial revolution powered by electricity. Invented in 1906, the Cooper Crouse-Hinds Condulet – coined by combining conduit and outlet – was the first electrical product designed to provide safe and convenient access to wiring enclosed in metal conduit. The Condulet product line has since grown to include more than 1,100 extensions, comprising six distinct families of products, and has become the highest selling conduit fitting product in the electrical industry’s history. One hundred years ago, electricity as an industrial power source was in its infancy. Contractors used existing natural gas pipes to run electrical wiring into factories, which required cutting the pipes to gain access to pull the wires. This left exposed conductors, resulting in frequent damage and costly replacements. To address this critical issue, Crouse-Hinds introduced the Condulet fitting.
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