# Capacitance of two wires with a grounded wire between

I have measured the capacitance between wires number, say, 1 and 3. With the wiree #2 just floating, the result was 390 pF. But after i have grounded the wiree #2, the capacitance was 220 pF. What is the reason of these results? The cable is FFC few meters long, so the wires just run in parallel.

• Do you really believe your question can be answered with the information you supplied. Do you have a schematic? How are the wires related to each other? Are there only capacitors involved or other components? etc., etc. – Barry Mar 28 '14 at 20:59
• What is the physical arrangement of the wires? If wire 2 is partially shielding between 1 and 3 that would a sensible result. – Spehro Pefhany Mar 28 '14 at 20:59
• What type of meter measured the capacitance? Ditto the above comments. – Andy aka Mar 28 '14 at 21:01
• Folks, the physical arrangement of the wires was already specified in the question title, but the poster has now added an additional description of the cable. – Chris Stratton Mar 28 '14 at 22:07
• The description of the wire arrangement is pretty ambiguous. Without some sort of diagram, and a rigorous definition of what "grounded" means here, I don't see how it can be answered. – Phil Frost Mar 29 '14 at 2:54

P.S. This is the representation using concentrated elements, you can create $\Pi$ or $T$ equivalents and connect them in a cascade to have a better representation of the circuit.