Inductance on lighting circuit

[Michaelwgroves]

i installed a new CU yesterday. During testing I noticed 15-30v on the 2-way lights circuits while off. I traced this back to cables being run together and caused by inductance. I can't separate the cables.
Should I worry about this, anything I can do?

Thanks,
Michael

 

[Andy-1960]

What were the cables that were causing the inductance?

 

[davesparks]

More likely to be capacitive coupling than inductance.
What instrument were you using to measure this potential?

 

[westward10]

Could be capacitive coupling between cables.

 

[Michaelwgroves]

Measured with Megger MFT1711

Some old, some new pvc cables. 1.5-10mm. Also new meter tails 25mm. But it's not just meter tails, it's everything.

 

[Ian1981]

I've experienced induced voltages but what is capacitive coupling between cables?

 

[Rpa07]

Same phenomenon I was aware! No?

 

[Pat H]

inductance is magnetic fields from one cable inducing a current in an adjacent cable. Basically like what happens in a transformer. Capacitance is when two cables are separated by a insulator (can be air) this acts as a capacitor and capacitors will allow AC currents to flow through them.
Both of the above can produce very low currents to flow. If the measuring device is high impedance then a relatively high voltage could be measured. At a load and it normally vanishes.

 

[Rpa07]

The kind of voltage that wouldn't be picked up by a Drummond lamp or a voltage indicator as these would require real power, not induced to activate.

 

[Michaelwgroves]

Should I be worried, or is it just one of those things?

 

[Rpa07]

Just one of those things - physics and all that!

 

[westward10]

Should I be worried, or is it just one of those things?

No and yes

 

[Octopus]

Just turn off the other circuits and the voltage will disappear...

 

[jaydub]

Out of curiosity, why could this cause a potential problem? See what I did there...

 

[davesparks]

Same phenomenon I was aware! No?

No, capacitance and inductance are different things