The circuits in an installation have an insulation resistance of 20MΩ, 34MΩ 18MΩ and 20MΩ if the insulation resistance was measured from the meter tails the expected insulation resistance would be
A) 5.40MΩ
B) 546MΩ
C) 5.46Ω
D) 5.46mΩ

Question

Quizplus · Accepted Answer

When measuring the insulation resistance of multiple circuits together, the overall resistance is lower than the individual resistances due to the parallel combination of resistances. The formula for total resistance $R_t$ in parallel is given by $\frac{1}{R_t} = \frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3} + \frac{1}{R_4}$. Using the given resistances, $\frac{1}{R_t} = \frac{1}{20} + \frac{1}{34} + \frac{1}{18} + \frac{1}{20}$ MΩ, which calculates to an $R_t$ of approximately 5.40MΩ.

The Circuits in an Installation Have an Insulation Resistance of 20MΩ