If you’re stuck on a site and having trouble with a CCTV installation and you don’t have your full tool bag with you, you can search for breaks in coaxial cables using a simple capacitance tester.

Remember that capacitance is the property of a system of conductors and dielectric that allows the storage of electricity when potential difference exists between the conductors. Its value is expressed as the ratio of a quantity of electricity to a potential difference and a capacitance value is always positive.

Capacitance is a measurement of a cable’s ability to store an electrical charge and it’s expressed in picofarads per foot (pF/ft). For the purposes of this test what you need to do is establish the capacitance of the coax (in the case of RG-59U it’s 53.1 picofarads per metre) and you multiply this figure by the known length of the cable run.

Once you have the nominal pf value of the cable run, attach the capacitance tester to the end of the coax cable and then divide the reading you get by 53.1. If the reading is different from the total capacitance of the cable then what that calculation gives you is the exact distance in metres from the point you tested to a break in the cable.

Another technique you can use with a capacitance tester if you think the break is at one end or another is to take a reading from each end of the cable. One end may show a large pf reading while the other end will have virtually no reading at all. In this case the cable break is at the end with the small reading.

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