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Capacitive reactance in twin and earth

Former Community Member
Former Community Member
I'm after some information regarding the cause of capacitive reactance which is part of the overall impedance of a circuit when carrying out loop impedance testing. 


I am not an electrician so apologies if this is standard knowledge to some of you. 


I understand how a capacitor works and what capacitance is. Since capacitive reactance is part of the three types of "resistance" of a circuit I am assuming that the reason this capacitive reactance is included is because twin and earth can to a lesser extent behave like a capacitor even when laid flat and not coiled? With AC power in the conductors I'm assuming that an weak electric field of attraction between the two conductors separated by the wire insulation forms. When the AC emf  passes the peak of the emf in the sine wave and current "flow" is now in the opposite direction from what it was moments beforehand then the induced emf created by the electric field between the two conductors results in a small reactive current flowing in opposing direction to the main current hence capacitive reactance?


 Thanks in advance
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    All cables have some form of capacitance, simply because the conductors act as plates, and the insulation acts as the dielectric between the plates.


    The longer the cable, the more capacitance, because the plates effectively increase in size as the conductors get longer.


    And that is what forms the capacitive reactance.


    In a multicore cable, coiling the cable has little, if any, effect on its capacitance.



    In a round 3-core (Line, Neutral and Earth) cable, with insulation on all 3 cores, there is equal capacitance between each pair of conductors.


    In flat twin-and-earth cable, there is equal capacitance L-PE and N-PE, but the capacitance between L and N conductors is much less, as they are further apart, and there are two layers of insulation.
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  • 0
    All cables have some form of capacitance, simply because the conductors act as plates, and the insulation acts as the dielectric between the plates.


    The longer the cable, the more capacitance, because the plates effectively increase in size as the conductors get longer.


    And that is what forms the capacitive reactance.


    In a multicore cable, coiling the cable has little, if any, effect on its capacitance.



    In a round 3-core (Line, Neutral and Earth) cable, with insulation on all 3 cores, there is equal capacitance between each pair of conductors.


    In flat twin-and-earth cable, there is equal capacitance L-PE and N-PE, but the capacitance between L and N conductors is much less, as they are further apart, and there are two layers of insulation.
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