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I am planning on using a 9 core wire to control 8 solenoid valves. 8 for the positive and the 9th for the common return. This is my first time ever using multiple positive wires with a common return and I thought of this scenario to which I cannot find an answer: If I have 24v 1A on the eight positive wires active at the same time, will I need to make sure the return is good for 8A or 1A? Does it even matter? Or am I missing a concept completely?

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    \$\begingroup\$ If all those valves can be on at the same time then yes, the common return will have to be able to carry 8A. \$\endgroup\$ Oct 24 '20 at 8:52
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    \$\begingroup\$ ... which means it has to be more than 8x the cross-sectional area of the 1 A wires, because a single big wire doesn't get rid of heat as easily as 8 small wires. \$\endgroup\$
    – Neil_UK
    Oct 24 '20 at 9:03
  • \$\begingroup\$ @John Petrak, Ah let me see. (1) If you are using the hobbyist relays like Songle 5V, I think you need around 70mA to activate the switch. For 24V relays, it should be much less that 70mA. In other words, not 1A (100mA) but only only <50mA. (2) If you are using Darlington arrays such as ULN2803 to direct control the solenoid, then the control signal should be very small. (I assume ULN2803 in open collector mode, solenoids get external power). I usually use AWG 26 connecting wires for these signals. (3) I don't use single common ground (to reduce solenoid switching noise. / to continue, ... \$\endgroup\$
    – tlfong01
    Oct 24 '20 at 9:08
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    \$\begingroup\$ i am still in early planning of the project so no real diagrams yet. I will have an esp32 microcontroller running at 3.3v connected to a 8 channel 5v or 12v powered relay (im leaning towards 5v because I prefer lower voltages when possible) then the 24V volts going into the relays of the relay board and then to the solenoids. solenoid url is popeproducts.com.au/irrigation/… but is does not give any detailed specs. My tests on it indicate it uses around 600ma when open. /to continue, \$\endgroup\$ Oct 24 '20 at 9:46
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    \$\begingroup\$ @tlfong01 The 1A was just to help me ask and understand the greater concept of a common return. The 9 core wire I have seams to be around 18 (1mm diameter manually measured by me) and it too is from the same manufacturer and does not give any meaningful specs (though it does say 0.5mm2 x 9 core. I am not really sure what that means gauge wise though. I am not sure if their controller allows several valves open at once given the gauge of the wire. Hence my question. \$\endgroup\$ Oct 24 '20 at 9:54

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