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# Zelio input maximum wire lenght

## 3 posts in this topic

Greetings, I have an schneider Zelio logic relay, and I want to connect to one of its inputs, a contact at a long distance, can you please tell me the maximum distance at that zelio relay input's sees that contact? Thank you.

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you don't say much.... what is the distance you are looking at? there is a huge difference between 100m and 100km. what type of input (AC/DC, voltage...)? every plc will have specs for the inputs such as minimum on voltage, input current or resistance. there are many factors such as voltage drop and interference (the longer the cable the more chances of it). if using AC things are a bit worse (capacitance, inductance, coupling..) then you build your model and compute/estimate max length. for example assuming that input is 24VDC type, at 24V input signal, input current is 6mA and min input voltage is 10V. 24V/6mA=4kOhm. if we model field wiring of that input as resistor, then we can solve this using knowledge of voltage divider: Vout=Vin*R2/(R1+R2) in this case Vout=10V Vin=24V R2=4kOhm and we need to solve for R1 (field wiring resistance). using basic algebra we get Vout*R1+Vout*R2=Vin*R2 R1=R2*(Vin-Vout)/Vout R1=4*(24-10)/10=5.6k but this is the worst case, ideally this would be zero. to play safe we should consider some safety factor, such as 20-25% meaning that our field circuit resistance should be under some 4.2k. next we look at wire size you have and it's resistance. basic resistance of uniform media (not corrected for temperature) is computed as R=rho*L/A so L=R*A/rho rho[Cu] = 16.78 n?·m = 16.78 * 10^-9 ?·m assuming we are using cable with wire cross section A=1.0mm^2 we get A=10^-6m^2 you get some 250km... keep in mind that you will need two wire for switch (so the max distance will be half of computed wire length) or max 125km. other factors also play role and will further limit this value. then of course you can model it using Maxwell equations but i don't think you want to go there... in general, larger wire means lower resistance and lower voltage drop. to increase immunity to interference you may use shielded cable.

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I had tried it but it not works for me .. can you have some another methods..