# Calculation of relay isolation

I am trying to calculate isolation of an relay in ohm. Can it be approached as calculation of resistance of solid materials?

$$R_{air} = ρ_{air} * \frac{d_{gap}}{A_{contact}}$$

Let's say resistivity of air equals 3.3e^15 Ωm and gap is 1mm between contacts with area of 1mm^2. As a result we get 3.3e^12. Can this be an approximate value to real isolation value?

Thank you.

Additional information: frequency range is from DC to 5GHz. Load voltage Vp is 24 and current is 20mA.

• It can be an approximate value yes. Nov 15, 2020 at 15:54
• Depends. "Isolation" may refer to isolation at DC, or a range of RF frequencies in general, or at a specific RF frequency. Your answer is good at DC.
– user16324
Nov 15, 2020 at 17:06
• Thanks for the comments. @BrianDrummond what should be the strategy for RF frequencies? Could you give a hint? Nov 15, 2020 at 18:10
• I only commented to avoid the trap of thinking a DC solution applied at high frequencies and finding out later, perhaps expensively, it doesn't. As a first step, I'd add that missing information to the question including the frequency range, power level, and characteristic impedance you're interested in.
– user16324
Nov 15, 2020 at 18:29
• I added some more details. Nov 15, 2020 at 18:45