Telephone: Part 4
North American Color Code
Until the late 1960s, telephone cable was insulated with red or white-colored compressed paper pulp (Figure 60). Underground cables were pressurized with air to repel moisture, and if the cable was severed by excavation, repairs often took days, as technicians had to electronically identify corresponding red and white cable pairs.
Plastic insulated conductor (PIC) using the North American color code replaced pulp cable. This system used 10 colors (Figure 61) allowing repair technicians to identify cable pairs visually. The primary five colors were blue, orange, green, brown and slate (gray). The secondary colors were white, red, black, yellow and violet. Pairs were divided into what were known as 25-pair binders whose first pair was blue-white. The numbering of pairs was color-based up to the 25th pair, which was slate-violet.
This Story is a Subscriber Exclusive.
North American Color Code
Until the late 1960s, telephone cable was insulated with red or white-colored compressed paper pulp (Figure 60). Underground cables were pressurized with air to repel moisture, and if the cable was severed by excavation, repairs often took days, as technicians had to electronically identify corresponding red and white cable pairs.
Plastic insulated conductor (PIC) using the North American color code replaced pulp cable. This system used 10 colors (Figure 61) allowing repair technicians to identify cable pairs visually. The primary five colors were blue, orange, green, brown and slate (gray). The secondary colors were white, red, black, yellow and violet. Pairs were divided into what were known as 25-pair binders whose first pair was blue-white. The numbering of pairs was color-based up to the 25th pair, which was slate-violet.
