I have recently been studying a problem with cables in trunking . The run of trunking is 150metres and there is 9x4c 1.5mm swith wires . the 4c is split into two pairs of switch wires a normally open pair and normal closed pair .
The problem is when a proximity switch down the other end of the shed that switches off the 110vac switch wire . The contactor that is being switched doesnt drop out because there is a 70vac remaining on the circuit.
I have even tried testing at the proximity switch and theres no voltage remaining when the switch shuts.
What im thinking is that there could be an induced voltage in the cable ?
When i disconnect the pairs of cables that arent in the section of the circuit thats causeing the problems ( the normaly closed) i can see for each of these 9 pairs that i drop out that the origanal 70vac problem drops by 6-9vac. Is inductance likely to cause this problem .

that sounds like an idea but would that stop the induction on the cable?

THe only other option that i had come up with was to link each Norm open switch at 1 end of the shed and then have just 1 pair running the 150 meters to the front instead of a pair for each run in series from front to back ( in affect 9 pairs each pair add up to 300m . 300x9 =2700m of 1.5 cable)
the new linkig at the back would reduce it to 3-400mtrs

Excuse my spelling on that diagram. Can't be bothered to change it.

Do you know what the contactor coil impedance is? If it's low then the above is all wrong!