Cable requirements for low-level measurements

Both coaxial and triaxial cables are available in low-noise versions and should be used for low-level measurements. Low-noise cables have a graphite coating on the inside to minimize currents generated by the triboelectric effect (see Section 2.3.4). Although leakage and noise currents are higher in ordinary coaxial cables than in low-noise cables, ordinary coaxial cables such as RG-58 may be suitable in some situations.
When measuring high resistances, the insulation resistance of the cable is important. Good quality triaxial cables use polyethylene insulation and have a typical insulation resistance of about 1 TΩ/ft from conductor to shield.
Cable resistance, capacitance, and leakage current[1] change as the length of the cable increases. It is therefore important to keep all connecting cables as short as possible. For example, a cable with a resistance of 1 TΩ/ft and a capacitance of 100 pF/ft has an insulation resistance of 100 GΩ and a capacitance of 1000 pF when the cable is 10 feet long.