Some non-electrical concerns to take into account when installing new cables

Installing new cables? There is a standard set of problems you need to be aware of. They aren’t necessarily electrical problems . . . .

The first is that you must realize you’re affecting the combustibility of the area where your new cable will be installed. The materials that make up the insulation are combustible. The plant tracks the amount of combustible material installed in each area. This is a requirement imposed by the NRC’s fire protection requirements. Cables that are pulled through conduit typically don’t count towards combustibility. In Section 3.6.3 of the Q&A of the generic letter I just linked to, we read:

Only oil in closed containers which are in accordance with NFPA 30 or electrical cables in metal conduits are not considered as intervening combustibles.

The conduit also provides a metallic barrier that offers physical protection to the cables from their surroundings. But cables installed in cable tray and in free-air must be tracked for their combustible content. So, you can all but count on impacting combustibility calculations that track the combustible materials in the area.

You might have to get the combustibility numbers directly from the cable manufacturer. “BTU per foot” might not be one of the technical specifications they document in their standard cable datasheets. But if you get stuck here, also check the plant’s combustibility calculation assumptions section. It might direct you to use some assumed combustibility value in lieu of the actual data.

Similar to combustible loading, you’ll need to be aware of any impact to heat-load calculations. As explained in other articles, current-carrying conductors generate heat as I2R losses. This heat emanates into the surrounding area. If this area is a critical area that must be cooled below a certain design limit (like the Control Room), you’ll have to check the heat-load calc to make sure there is margin available.