Power plant practices to ensure cable operability

What does cable operability mean?

The basic function of electrical cable in a power plant is to transmit instrument signals, control signals, and electrical power. In most non-nuclear power applications, cables are not required to function under adverse environmental conditions.

For these cables, operability means that the cable will continue to conduct the signal or power, while maintaining satisfactory insulation characteristics such that unacceptable levels of signal attenuation or shorting do not occur.

Recently, cable installation and operability concerns were raised about low-voltage cabling in nuclear safety-related service that could potentially be exposed to accident environments.

The concerns were first raised as a result of installation practices that were alleged to have deviated from industry “standard, accepted, or good practices.”

The deviations consisted of excessive lengths of unsupported vertical cable drops, reduced bending radii of cable during and after installation, installation of new cable in raceways in a manner that could damage existing cable, impact damage to cable during installation, and other related handling and installation concerns.

Scope of research

The scope of the research covered the following specific areas and their relevance to cable operability:

• General cable construction features
• Cable applications
• Physical installation practices
• Environmental qualification practices
• Record of past cable performance
• Differences in medium-voltage power, low-voltage power, control, and instrumentation cable stresses during service and testing Efficacy of “standard” in-situ testing for:
  1. Suspect installations
  2.  General cable condition monitoring
• Significance of available ground plane at the surface of cable insulation in relationship to cable condition monitoring via electrical tests
• Cable performance in support of connected devices during accident conditions
• Operating voltage versus rated voltage
• Relationship between required safety function and intrinsic cable capability
• Efficacy of existing industry standards, codes, and guidelines