Appliance connected to two separate (240V AC) power sources - how to switch? - Page 1
Forum section: electronics / beginners

author: gorish
author_rank: Newbie
timestamp: April 26, 2023, 04:17:27 am
content: I'm tearing my hair out on this one. Can anyone advise?Here's the situation:I am sharing an (expensive) irrigation water pump with a neighbor - we are on separate sides of the river.I would like to set it up so that when he uses the pump, it draws electricity fromhispower supply and when I use the pump, it takes electricity from mine.The simplest solution seems simply to be that I plug the pump into both power supplies simultaneously (with their own separate switches). If I switch on my side, the pump will run and irrigate my land. If he switches his side, the pump will run and irrigate his land. (We would open the valve on our respective side of the river to control the water flow.)What I'm worried about is: what if we both inadvertently switch on the power at the same time? It's surely not like an AC system with two batteries wired up in parallel, which doubles the voltage - or is it? Would the pump receive 480V of AC current because it's being power by two separate power supplies. Or does the grid simply deliver the standard 240V regardless of how the electrical flow is routed, or whether it's doubled up or not?I've been looking into Automatic Power Switches, but these only seem to be for switching from one source to another when the other source is lost. They don't seem to be designed for choosing between two sources simultaneously (or "splitting" the power drawn across two different sources simultaneously). And an interlock switch is practical coz we are physically separated by the river - so only one of us can have access to it.Any ideas? Do I need to worry at all (i.e. can I allow for the situation where we both switch on the pump at the same time)?The other thing I've been trying to figure out is a dual switching mechanism (like for lights, where two switches at different locations can switch the same light on or off). But I can't figure out the wiring for the reverse case - to select the supply, rather then switch on or off the load (light/pump/etc.).

author: james_s
author_rank: Super Contributor
timestamp: April 26, 2023, 06:05:41 am
content: Use a double throw contactor and wire one power source up to each set of contacts and take the pump power off the common contacts, connect the relay coil to a microswitch mounted on the valve so that the relay will energize to switch to the correct power source when the valve is set that way. Or you could use a pair of mechanically interlocked contactors of the sort used in automatic generator transfer switches. Either way makes it impossible for the two power sources to get connected together, which is what you want to avoid.If the pumps are single phase then a DPDT contactor will work, if 3 phase then you need a 3PDT.

author: gorish
author_rank: Newbie
timestamp: April 26, 2023, 06:51:19 am
content: Thanks, but I'm afraid I don't understand.I've been searching for how to wire two DPDT switches so that when mine is on it prevents the other switch across the river from connecting to the power source when on. And when the one across the river is on it prevents my switch from connecting to the power source when on. In other words, to get any power, only ONE of the switches can be on at any time. If both are on (or obviously when both are off) then there is no power.Update. I think I've figured it out, but I see that there must be an absolutely foolproof way of not mixing up live & neutral. We will have to share the neutral line (and I don't know if this is okay, as our mains supplies come from two separate transformer circuits). Also if both switches are ON then both live parts of the separate household circuits are joined up too!The (two-pronged) plugs here - in Thailand - can be inserted into the sockets either way. I could of course attach 3-pin plugs and change the mains outlet to the grounded variety. (There is no ground in Thailand. Devices like the pump have a separate earth wire to be grounded separately on the property with a copper ground post.)https://ibb.co/zQL0Yy6(is this right?)

author: vk6zgo
author_rank: Super Contributor
timestamp: April 26, 2023, 07:03:41 am
content: Quote from: gorish on April 26, 2023, 04:17:27 amNo two batteries inparalleldon't double the voltage------the voltage stays the same, but the current available from the parallel batteries will double.Equally, two 240v ac supplies in parallelfrom the same source, with exactly the same phasewill stay at 240v.If your neighbour's ac supplyis on a different phase feed "all bets are off!"(sometimes explosively "off').It would probably be illegal to use the simplest set up where there is a possibility of having both supplies on at the same time, as the authorities have no way of easily ascertaining whether you both have the same phase of Mains feed.The best ways to do such things, & what would be done commercially, is to use one of the methods described byjames_s

author: Ian.M
author_rank: Super Contributor
timestamp: April 26, 2023, 08:40:42 am
content: Its illegal because such a dual feed setup could back-feed the farm on one side of the river if power was out on that side, from the other side that still has power, possibly even back-feeding power to other neighbours, endangering utility workers working to restore power. *DON'T* even think about trying to DIY the switching for this.One legal, and electrically safe (if properly installed) option would be to fit a privately owned electricity meter in the feed to the pump, with two switches, one to run the pump from the extra meter, and the other to run the pump bypassing it. Then whoever is *not* supplying the power would use the switch that runs it from the meter and would reimburse the one supplying the power for the electricity used. Add solenoid controlled valves activated by the switches to direct the water flow, and its pretty much foolproof, as each switch will then only deliver water one side.

author: 807
author_rank: Frequent Contributor
timestamp: April 26, 2023, 10:23:43 am
content: As advised above, don't even think about simply connecting both mains supplies to one pump. You would be "supplying" mains to your neighbour & vice versa. Very dangerous.Whilst I think that you should get a qualified guy to do the work, in general, if you want to isolate each supply from the pump when the other is using it, then a mains relay should do it. One of you will take priority by operating the relay on your side. I imagine it will have to be a fairly sustantial relay to operate a pump.A quick hand drawn attachment...

author: BeBuLamar
author_rank: Super Contributor
timestamp: April 26, 2023, 11:06:29 am
content: How far is the pump from each power source?

author: gorish
author_rank: Newbie
timestamp: April 26, 2023, 12:03:41 pm
content: BeBuLamar, the power sources are about 50m away from the pump, which is in the middle of the (10m-wide) river. It's about a 1km trip to get to the other side via a nearby bridge.So far, the solutions seem overkill. The DPDT seem to be the right track, but it's flawed. I need a switching mechanism where the power from my side is connected ONLY if the switch is on AND the switch on my neighbour's side is off. (And vice versa.) It doesn't seem complicated, but I'mtrying to find the right way to isolate each of the circuits from each other.The simplest solution would be for my neighbour to unplug (or switch off) the outlet on his side before I plug in/switch on the outlet on my side. And for me to do the same when he wants to use the pump. But that would mean we'd have to coordinate with each other each time, which isn't always possible. We could make it a rule that after using the pump, the mains on our side is disconnected each time.But what if one of us happens to switch on the pump, not knowing that the other person is currently using it? Then we'd have a situation when both mains systems are live and operating the pump at the same time!At the very least, if an LED could light up on the one side when the other side is running the pump. Then we'd know it's not safe to turn on the pump, and to wait until the LED goes off. (There's of course, the small possibility that we might both switch on the pump at exactly the same time.)For now, I'm entertaining a lo-tech solution. Tie the plug end of the pump cable to a zipwire across the river, and whoever wants to use the pump pulls the plug to his side and physically plugs it in to the mains on his side.There must surely a simple, elegant solution to this problem!

author: themadhippy
author_rank: Super Contributor
timestamp: April 26, 2023, 12:30:25 pm
content: Simplest solution is buy another pump so youve got 1 each

author: Siwastaja
author_rank: Super Contributor
timestamp: April 26, 2023, 12:51:24 pm
content: It's something you can't safely do yourself and requires special understanding. You need to hire a legal and competent electrician to do the job, with suitable components.It would be far easier to just come to an agreement over sharing the costs. How much electricity does that pump use anyway? Some tens of $ worth a year? Maybe consider having a meter installed (if the pump is connected using a plug, you can buy a cheap Kill-a-Watt type device). Then you could calculate the cost of electricity every year or so and agree that one of you two pays the other for half of the reading.

author: Seekonk
author_rank: Super Contributor
timestamp: April 26, 2023, 01:04:35 pm
content: If I had this situation I would have a box with two keyswitches so each could turn on the pump. His keyswitch would turn on a power meter and the pump which would record how much power he used. These meters save energy use and removing power to device will stop it recording. Read it at the end of the month and settle up. There are cheap power meters where you can enter price per KWH making it simple. Probably way cheaper than the cost of wire to a second power source.

author: WattsThat
author_rank: Frequent Contributor
timestamp: April 26, 2023, 01:09:40 pm
content: Two contactors required. Each device needs pump motor rated contacts and a normally closed auxiliary switch.Relay A coil is in series with relay B auxiliary switch. B coil is in series with A auxiliary switch. Only one relay can be energized at a time as it prevents the other coil from energizing due to the open auxiliary contact in series.Neighbor A switches on power to the pump, relay A pulls in, powering the pump and this prevents relay B from pulling in even when power is applied. Neighbor B cannot run the pump until neighbor A removes power.Valve control is not addressed. It could be as simple as solenoids in parallel with each contactor coil.Proper fusing and ground fault protection would be required at a minimum.

author: Miha
author_rank: Contributor
timestamp: April 26, 2023, 01:46:26 pm
content: But, as mentioned above:You need to hire a legal and competent electrician to do the job, with suitable components.

author: sparkydog
author_rank: Regular Contributor
timestamp: April 26, 2023, 04:32:09 pm
content: I think what you need (hopefully I drew this correctly) is this circuit:(Note: I think this is essentially what WattsThat was trying to describe.)You need two three-pole, dual-throw contactors, preferably ones whose coils run off the same VAC as the motor¹. Since three-phase power is a thing, these shouldn't be too hard to find. (Note: I'm assuming your motor runs off single phase; if it's three-phase, that's going to make things more interesting.) You also need two switches that are capable of switching the motor². The switches go on either side of the river, while the contactors go with the pump.The wiring is where the magic happens. Your AC-L runs to 1C onyour neighbor'scontactor, back from 1NC to your switch, then from the switch toyourcontactor's coil and 2C. Your AC-N connects to the coil and 3C on your contactor. The motor's AC-L connects to 2NO onbothcontactors, and its AC-N to 3NO on both. Your neighbor has the exact mirror of your setup.With neither contactor energized, no power is connected to the motor. When you flip your switch,yourcontactor becomes energized... and interrupts power to your neighbor's switch. Now, even if your neighbor flips his switch, nothing will happen until you turn your switch off. The only way to energize both contactors at once would be to flip both switches atexactly(within milliseconds) the same time. (Which will also cut power to both coils, but possibly Bad Things will happen at that point. Still, the chances of you both flipping your switches at the exact same instant are pretty low.)It shouldn't be too hard to add some indicator lights, which is probably a good idea.¹ Since the contactor coils are driven in parallel, you can add a transformer or PSU if needed.² If standard switches aren't suitable, you can replace the switches shown in the circuit with another pair of contactors and drive those however is convenient.

author: james_s
author_rank: Super Contributor
timestamp: April 26, 2023, 05:10:44 pm
content: Quote from: gorish on April 26, 2023, 12:03:41 pmThe schematic 807 posted is exactly what I had in mind, except you can improve it by powering the contactor coil through a microswitch mounted to the valve, that way if the valve is set to give your neighbor water then the pump will only respond to his power source, and when it's set to give you water, it will only respond to your power source. Due to the fact that the power sources are connected to the fixed contacts that can never connect to each other this is safe.

author: Jeff1946
author_rank: Regular Contributor
timestamp: April 26, 2023, 05:28:53 pm
content: On his side of the river double pole, on-off switch, output goes to your side. On your side, double pole three position switch connected to pump. Say position one goes to power from his side, position two is off, and position three to your side. Off position would be used to service pump. Probably good to have a lamp across power from his side so you know if his switch is on.

author: james_s
author_rank: Super Contributor
timestamp: April 26, 2023, 05:40:32 pm
content: Reading the original post again, there are two valves and it sounds like what you want is XOR logic. If your valve is open then allow the pump to turn on and select your power source as the feed. If his valve is open then allow the pump to turn on and select his feed. If both valves are closed, disable power to the pump, and if both valves are open, disable power to the pump. You could do this all with relay logic fairly easily, or you could take the electronic route and use logic gates, or throw a microcontroller at it but relay logic seems simpler.

author: Zero999
author_rank: Super Contributor
timestamp: April 26, 2023, 06:33:36 pm
content: How much electricity does the pump use? Is it even worth arguing over?You could just take turns in plugging it in, or just do a rough calculation on how much it costs to run and reimburse the person who's supply its connected to.

author: james_s
author_rank: Super Contributor
timestamp: April 26, 2023, 11:44:20 pm
content: An irrigation pump could easily be 5-10kW or more, likely pretty significant, it could be calculated based on run time, although I do think the power source switching is an interesting technical challenge. It's pretty trivial to wire up a double throw contactor to select between two power sources followed by a single throw contactor to control power to the pump. Then it's just a matter of controlling power to the contactors to determine where the pump gets power.

author: themadhippy
author_rank: Super Contributor
timestamp: April 27, 2023, 12:31:32 am
content: Quoteyou've obviously never been to Thailand,a couple of there piccys of there fine work,in the first is the cable used to power the stalls at a night market that was being set up,by what looked like council workers.,the second, that panel is live and the fence is busted just out of shot so you could easily walk up to it and stick your fingers in

author: Jwillis
author_rank: Super Contributor
timestamp: April 27, 2023, 01:37:38 am
content: You could use a ATS (Automatic Transfer switch)How its wired would depend on the brand.

author: WattsThat
author_rank: Frequent Contributor
timestamp: April 27, 2023, 02:08:57 am
content: A picture is always worth a thousand words:

author: SmallCog
author_rank: Frequent Contributor
timestamp: April 27, 2023, 02:09:11 am
content: It's simple enough to set up using contactors although it's definitely in the realm of "if you need to ask you shouldn't be messing with it"Speak to an electrician, particularly one who works with industrial equipmentHe can also set you up with a control box from each side of the river and actuate automated valves so that water is directed to the person whose electricity is being used without needing to change valves manually

author: ejeffrey
author_rank: Super Contributor
timestamp: April 27, 2023, 02:24:16 am
content: Quote from: Siwastaja on April 26, 2023, 12:51:24 pmThis. If your usages are not approximately equal so you can just split the bill then find a way to log usage hours for the person who doesn't pay the power bill. Also useful if you want to split maintenance costs.

author: BeBuLamar
author_rank: Super Contributor
timestamp: April 27, 2023, 09:16:57 am
content: 50 meters is quite long to run 220VAC cable with any significant current. Also the transfer switch has to be near the pump which I believe is under water.

author: Terry Bites
author_rank: Super Contributor
timestamp: April 27, 2023, 11:31:54 am
content: Manual and Auto. only one side can have the control over the default power source- if you both try and put on the power simultaneously, a fault will occur with uncertain (but bad) consequences. Set it up on your side so that when you turn off he has the control.Earthing may present a problem- it depends on your local codes and your Neutral<> Earth arrangments.An earth conecting your system to his may present a conflict situation for your individual RCDs.Whose side is leaking to who?If you can safely operate without a common earth then do so.The contactors shown here are LC1D12 P7s but other 240V DP types will work.I'd go for the manual switch or better still just back charge him for your power- be good to each other.Trade for goods and beer.

author: james_s
author_rank: Super Contributor
timestamp: April 27, 2023, 05:48:17 pm
content: Once you have the contactors set up then you just need a control signal for that. It would be fairly easy to set it up so that there is no master and both sides have the ability to switch the power source, essentially just a 3 way switch. I like the idea of mounting microswitches to the valves though so that opening the valve automatically sets the pump to draw power from that side.

author: RJSV
author_rank: Super Contributor
timestamp: April 27, 2023, 07:51:54 pm
content: Hey, uh...HEY GUYS :You are talking right over this OP's head, as if he is to sort out, 9 different solutions. Let's say, for practical sense, let's say that OP makes a little wiring mistake, every so often, like 1 out of every 8 connections.Flooding poor OP with 'electrical' solutions, partially outlined and with phrases like ' you can figure out the rest,...or put in AN ARDUINO...' don't go anywhere. That boat dead in the water.How about: Each person moves their entire house, out to middle of river, WITH ONE PUMP, ONE SWITCH.Then, irrigation done, you'd have a rope, for pulling your house back to your side of the river.Problem solvde

author: bdunham7
author_rank: Super Contributor
timestamp: April 27, 2023, 08:05:09 pm
content: I'm just curious--where is the pump located--in the river? And I suppose that at least one of the pipes and electrical feed cables has to cross the river?

author: Jwillis
author_rank: Super Contributor
timestamp: April 27, 2023, 10:43:08 pm
content: Quote from: BeBuLamar on April 27, 2023, 09:16:57 amBest guess its a submersible pump or floating on a "raft". Either works fine. All wires can be feed down a conduit along the water pipes that go to either side of river.Using a certified transfer switch (automatic or manual) is the best and safest solution as your probably not defeating local electrical and safety regulations. Keep in mind we don't want to burn a persons house down with DIY Hodge Podge. All electric motors carry an inherent in rush current , and the switchs and relays need to be able to handle that. High power transfer switches are designed for that.I don't know what the OP's budget is. Maybe an "agreement of use" would be the best approach.

author: 807
author_rank: Frequent Contributor
timestamp: April 28, 2023, 09:01:59 am
content: The problem with any manual switching solutions, is that it's possible that whoever has control of the changeover switch could easily forget to switch it back to the neighbours side, leaving the neighbour unable to turn on the pump.That's why I suggested an automated (relay) solution in my earlier post. When the OP switches on the supply to the pump, the relay switches to his supply. When he switches the pump off, the relay will switch to his neighbours supply automatically.

author: Ian.M
author_rank: Super Contributor
timestamp: April 28, 2023, 09:41:11 am
content: If the neighbours are on different mains phases (a >2/3 probability), there will be 380V RMS between the two L lives + switching transients. *ANY* DIY solution that attempts to implement a transfer switch using relays or 240V rated contactors is likely to fail dangerously.

author: Watth
author_rank: Frequent Contributor
timestamp: April 28, 2023, 10:37:56 am
content: A solution could be to have the plug connected to a short cable with a plug.You place nearby two sockets, one from your home, the other from your neighbour's.When either one of you wants to use the pump, you plug it to the proper socket.- This prevents the risk of connecting the two circuits together.- It's quite easy to install.I added a very professionally made schematics (which includes the sun on the top left corner, as is required by law).

author: tooki
author_rank: Super Contributor
timestamp: April 28, 2023, 12:45:30 pm
content: I guess you missed the part about the pump being in the middle of a river, with each owner on opposite sides of the river.

author: Ian.M
author_rank: Super Contributor
timestamp: April 28, 2023, 02:07:59 pm
content: Run an extension lead across the river from neighbour B with the socket end on A's side. When A wishes to use the pump, he transfers its plug from B's extension socket to his own power socket and back to B's socket afterwards. When B wishes to use the pump, he simply plugs his extension lead into his power socket. An indicator light on a pole, wired in parallel with the pump, visible across the river would be a useful addition.Of course this relies on A always moving the plug rather than just unplugging it, (so if one of the neighbours is flakier than the other, they should be B), but its cheap and possible to implement safely with DIY electrics using commonly available parts.

author: james_s
author_rank: Super Contributor
timestamp: April 28, 2023, 10:55:05 pm
content: Quote from: Ian.M on April 28, 2023, 09:41:11 amSo use a 600V contactor, they're readily available, in fact most of the contactors I've seen are rated for 600V.

author: EPAIII
author_rank: Super Contributor
timestamp: April 29, 2023, 08:41:04 am
content: I do not think any of the circuits suggested above would be safe. I tried to draw a more or less standard motor control with two four pole relays/contactors and could not completely eliminate the possibility of a large mushroom cloud if both start buttons were pressed at the exact same time. That is not likely a frequent event, but it could happen. Part of the problem here is even if both parties are connected to the same power grid, the phasing could easily be reversed which would produce a pair of direct shorts if both relays/contactors were activated at the same time and that, even if only for a fraction of a second, could be a very exciting event.I think this would require some kind of computer control where the software would only look at ONE start input at a time and could only activate one relay/contactor at a time. This software could, of course, switch back and forth between looking at first one and then the other in rapid succession - small fraction of a second for each. Look at Input A for 1/1000th second and then look at B for the next 1/1000th second, then back to A, etc. If either relay/contactor was activated, then the software would completely ignore the inputs until it was turned off. That would give the appearance of first come, first served, but would completely eliminate the possibility of both relays/contactors being on at the same time.And such a computer board/software control would also allow the control wiring to be LOW Voltage instead of line Voltage, which would be much safer. Line power would only go to the relays/contactors.NOW, I know nothing about what is and is not LEGAL in your country. I strongly suggest you find out BEFORE doing anything.

author: geggi1
author_rank: Frequent Contributor
timestamp: April 29, 2023, 09:15:33 am
content: The simplest way is to have a manual switch-over.There are avalable switch-overs that are 1-0-1 type that have one input and two outputs. In your case it would be used the opposite direction.You might find these online as manual transfer switch.Just put this up front of what ever control gear is used to control the motor and you just switch the supply.There will be no risk of back-feed because the supplies at totally separated.

author: Ian.M
author_rank: Super Contributor
timestamp: April 29, 2023, 10:58:37 am
content: I think reply #7 slipped past you:Quote from: gorish on April 26, 2023, 12:03:41 pmA'int nobody got time for a 2km round trip to turn the pump on or off.

author: BeBuLamar
author_rank: Super Contributor
timestamp: April 29, 2023, 11:34:22 am
content: Quote from: Ian.M on April 29, 2023, 10:58:37 amYes the OP answered my question about distances and when he posted the answer I have no idea how to do it as it way too far and I believe the pump is in the water so the switching device is best place at the pump but it's in the water so which side of the bank do you put the switching device? You also have to run power line across the river to get the power from the other side to the switching device if you put it on the bank.So really after he repied with the distances I really have no idea on how to do it. Also how much current this pump need? at 50m length minimum the current draw is a big concern.

author: themadhippy
author_rank: Super Contributor
timestamp: April 29, 2023, 01:25:03 pm
content: Quoteuse a motor reversing contactor,youd need to rewire the connections,but the mechanical interlock will avoid any smoke escaping

author: Ian.M
author_rank: Super Contributor
timestamp: April 29, 2023, 01:39:48 pm
content: I suspect that unless the pump is ludicrously expensive, the cheapest option to safely draw power from the correct side of the river, without having to manually move a plug, would be a second pump!

author: SmallCog
author_rank: Frequent Contributor
timestamp: April 30, 2023, 12:11:35 pm
content: Quote from: EPAIII on April 29, 2023, 08:41:04 amI agree on about using ELV control circuitry (low voltage here is mains) and in industry this would typically be 24VDCIf you’re using a changeover style system it can only connect to one power source, the interlocking prevents joining of sources.You could set it up to lock out a control request from the neighbour when already running, or to stop, change source, and restart. I’d include a timer to delay restarts, pumps don’t like turning off and on quicklyIt’s definitely something a PLC could do (I’d not trust this to an arduino) but it’s certainly able to be done safely using typical switchboard equipment.I’m not however familiar with the OP’s local electrical regulations to know if it’s legal.

author: RJSV
author_rank: Super Contributor
timestamp: April 30, 2023, 03:10:40 pm
content: Regarding ABANDONMENT OF DUAL USE:Nice exercise. Totally impractical, possibly expensive. But, interesting problem, why not create a separate thread, so OP doesn't, also, get mired in ever-expansive speculation. !Seriously, might be possible to have pump controls, and water delivery, to only one side. Then, by way of solenoid valve(s), (again, more complexity, for OP to digest!), be able to direct the water stream to a second pipe, that crosses over to side 'B'.This whole, expansive dialog is starting to look like some dysfunctional government agency job (in some countries).

author: BeBuLamar
author_rank: Super Contributor
timestamp: April 30, 2023, 04:33:36 pm
content: The distance from power source to the pump is huge 50 meters. I believe the pump sits in the middle of the 10 meter wide river. Where do you put the contactor?

author: james_s
author_rank: Super Contributor
timestamp: April 30, 2023, 08:12:05 pm
content: Quote from: EPAIII on April 29, 2023, 08:41:04 amThat's why I suggested using either a double throw contactor, or a pair of mechanically interlocked contactors. Both of these solutions are readily available and are used for generator transfer switches where this exact same scenario exist of a load sharing two power sources that cannot be connected together without very bad things happening. This is a solved problem.

author: james_s
author_rank: Super Contributor
timestamp: April 30, 2023, 08:13:44 pm
content: Quote from: BeBuLamar on April 30, 2023, 04:33:36 pmOn one side or the other. All of the control components would go in a box on one of the two properties, and then a wire from there goes out to the pump and another wire goes from the other property across the river to the control box.

author: Jwillis
author_rank: Super Contributor
timestamp: April 30, 2023, 10:50:07 pm
content: Something like this. The only thing that may become a problem would be the voltage drop across the distance. I'm not sure of available resources. Source B would require a higher gauge wire to accommodate the distance. Over a 10AWG wire the voltage drop is around 3.5 volts @ 20 Amps over 50 metres. The voltage drop would also be dependent on the current draw of the pump.A very cheap solution would be to have the pump connection attached to a rope across the river that could be pulled from one side or the other. The rope could be strung across with a couple poles like a cloths line.

author: coppercone2
author_rank: Super Contributor
timestamp: April 30, 2023, 11:07:40 pm
content: a transfer switch should be ok because thats what the electrician will do to protect your generator from those tree guys

author: vk6zgo
author_rank: Super Contributor
timestamp: May 01, 2023, 12:06:27 am
content: Quote from: RJHayward on April 30, 2023, 03:10:40 pmBack in the day, the govt organisation that I then worked for in Oz installed hundreds of changeover systems designed for switching from Mains to Emergency Power Plants.These could either work automatically upon loss of Mains, or "manually" following the operation of a push button.Around the same time, private sector organisations also installed similar systems.These were 3ph units at Broadcast/TV, & Communications sites.Such equipment was/is mature technology, & operated trouble free for decades.It wasn't cheap, but a single phase unit of much lower power rating should be reasonably economical.Trying to "bodge" something up is fraught with peril, so if getting it done properly approaches the price of a second pump, the latter is a better solution.

author: SmallCog
author_rank: Frequent Contributor
timestamp: May 01, 2023, 02:00:45 am
content: Quote from: BeBuLamar on April 30, 2023, 04:33:36 pmNot at all uncommon for submersible pumps to have very long cables, especially when used in bores or wellsThis may even be a bore or well pump fitted with a shroud to aid motor cooling and positioned in the river.

author: james_s
author_rank: Super Contributor
timestamp: May 02, 2023, 04:56:10 am
content: An irrigation pump can cost several thousand dollars, a transfer switch is a few hundred. Especially given this is in a country where cobbled together stuff is typical this seems like a reasonably worthwhile project.

author: RJSV
author_rank: Super Contributor
timestamp: May 02, 2023, 11:07:45 pm
content: If folks are, actually, determined to get the shared pump up and running then so be it, will try more suggestions:How about an unconditional system, where each side gets, say, 20 minutes twice each day, (along with appropriate measures to safely overflow)?By the way, if this is meant for direct, immediate irrigation, that's easier than if it's filling a drinking water tank (on each side). If it's too much delivery, and power use, maybe dial that back as the season unfolds.Assuming there are 'immersible solenoid valves' how about putting one valve, and output pipe, for each side, plus put the side 'B' request switch, to cross over to side 'A'. Then, all circuitry and logic relays could be on side 'A'.This physical arrangement might be good, whether or not the delivery is unconditional, or not.(Unconditional delivery, with attendant overflow directed back into river, has no need for request buttons).Note that the timer oriented option could be accomplished, skipping need for a dual contactor, and associated request switches, and A/B isolation lockout.

author: RJSV
author_rank: Super Contributor
timestamp: May 02, 2023, 11:24:27 pm
content: ...once I've started thinking along the lines of simply eliminating that contactor, how about:Put everything on side 'A', on a proper heavy duty timer(s), maybe even skipping using solenoids.Water dumps, first, into a 'splitter tank' that more or less is adjusted for whatever ratios desired, like 45% and 55% and then simply run the 'B' side water pipe back across river.Farmers can estimate the power cost sharing, fairly accurately.AND: Don't discount the future, as maybe after a year or two the two farmers can always modify things, assuming they didn't spend too much on initial installation.

author: EPAIII
author_rank: Super Contributor
timestamp: May 03, 2023, 06:56:00 am
content: Perhaps I missed something in the discussion so far, but it seems that too many pesky details are missing.Exactly where is this pump located? The middle of the river seems logical, but is that the case? And is the motor fro the pump ABOVE the water or immersed in the water? Or is it on one bank, above or below water level, dry well or immersed, with pipes leading to the water intake and to the areas to be irrigated? Those answers are a starting point in this problem and we don't have them.Next, how is it powered? Again, the logical answer seems to be a SINGLE, water tight cable that goes ..... OK, WHERE does it go? Or has it even been installed yet? Where should it go? Where is the switching point located or going to be located?Or, do you envision TWO water tight cables, one to each river bank? That would mean TWO switching points which need to be synchronized to avoid sparks and smoke.Next point would be are the power lines on both sides of the river coming from the same phase of the same power distribution system? If this condition can not be guaranteed under all circumstances, including those NOT under the control of either party, then there must be a fool proof switching system.I suggest we stop wasting our time until at least these questions are answered. Then, there will probably be more questions before a sensible system could be designed.

author: EPAIII
author_rank: Super Contributor
timestamp: May 03, 2023, 09:19:24 am
content: After thinking about this a little more and re-reading the OP's posts, I think this may be a good and safe way to do it. And about as simple as it can get, given the problems involved.I am assuming three locations are involved: the two control stations on both sides of the river and the pump's location which may or may not be submerged in the river itself. There must be a cable that connects these locations and it seems that the simplest way would be to run from Side 1 to the pump and then to Side 2. This cable must carry the power from each side to the motor so two heavier conductors must be present for that. I don't know the current that the motor draws so I can't suggest any wire gauge. The other three conductors in the cable can be smaller or a second, lighter gauge cable can be used. They only need to carry enough current to initially engage the contactors.Two of each component is needed except for the fuses where four are required. The fuses are sized to carry the full current of the pump motor. So are the main two, normally open contacts on the contactors. The other, auxiliary contacts on the contactors only need to carry the coil current of the contactors. Many contactors are made with such light duty, auxiliary contacts. I show these auxiliary contacts as two separate sets of contacts, but since they are connected on one side, a single, SPDT (Single Pole, Double Throw) set of contacts would work. The switches are momentary contact, push buttons: Normally Open for the STARTs and Normally Closed for the STOPs.How it works:Each of the START buttons is powered from the 24 VDC power supply on the opposite bank. This Voltage is passed through the Normally Closed auxiliary contacts on the contactor at that location. This guarantees that the opposite bank's contactor must be OFF for the START button on each bank to function. But once the contactor on a given bank is activated, the normally open, auxiliary contact on that contactor closes and provides the coil's holding current to keep the pump on. The STOP buttons open the contactor's coil circuit, stopping the pump motor. This arrangement ensures that both contactors can not be activated at the same time.The fuses are included to provide protection against several possible scenarios. First, is the obvious chance of a short circuit. But if both START buttons were to be pressed at the same time, the contactors might switch ON and OFF rapidly and this could produce a short between the AC power lines on the two sides of the river. If this should happen, the fuses should blow, protecting the wiring on both sides. These fuses should have a high arc-over rating. I am not sure if circuit breakers would be suitable.

author: Jeroen3
author_rank: Super Contributor
timestamp: May 03, 2023, 09:45:25 am
content: By far the cheapest option is to install a power meter with two counters that accumulate based on which input is activated.One contactor then enables the pump, if anyone requested pumping. This can be done even with wireless or remote relays, no new cabling required. The neighbors request signal activates an input on the power meter, switching tarrif, starting the other accumulator.You may even get a nice Arduino Opta project out of this.Establish a billing period and do some math and invoicing.Only drawback, when you are both taking water only one of you pays.The switchover solutions proposed are against regs almost everywhere.

author: 807
author_rank: Frequent Contributor
timestamp: May 03, 2023, 10:40:22 am
content: Quote from: EPAIII on May 03, 2023, 09:19:24 amWhen the START button is pressed and the n/o relay contact switches over, 24v will be applied to the other 24v supply output until the START button is released. It may be OK as it is, but I would be tempted to put a protection diode in series with the positive supplies of both 24v PSU's.Also, your circuit, while allowing both to have first choice of using the pump, does rely on the other having the 24v supply plugged in at all times.I've added a neon indicator to my ultra simple circuit to show when the neighbour is using the pump. It would be placed in the relay box on the OP's side. It doesn't stop the OP from taking control of the pump, but then his neighbours valve would be open, so wouldn't do it anyway.

author: james_s
author_rank: Super Contributor
timestamp: May 03, 2023, 08:16:28 pm
content: Quote from: EPAIII on May 03, 2023, 09:19:24 amNo way, that proposal is dangerous and would be illegal in most parts of the world. You absolutely MUST use either mechanically interlocked contactors that CANNOT under any circumstances both close at the same, or a double throw contactor that cannot possibly ever connect both feeds at the same time thus potentially backfeeding a circuit on the other side. You cannot rely on fuses here, they don't protect against the scenario where the circuit on one side is shut off at the panel and gets energized from the other side. There must be no possible way for a control system fault or misuse to cause both feeds to be connected simultaneously, this is absolutely mandatory.As I've said before, this is a solved problem, double throw contactors and mechanically interlocked contactors are readily available and widely used for backup generator transfer switches.

author: EPAIII
author_rank: Super Contributor
timestamp: May 04, 2023, 10:04:29 am
content: Well, I thought of the two power supplies fighting each other after I posted. But it was 5 AM and I went to bed. Besides, it would only be for a second or two while the START button was held down so I am not so sure diodes would be needed.And yes, the other guy's power supply, actually both power supplies would need to be ON at all times. That's a FEATURE, not a drawback. With modern, switching power supplies that is not much of a power drain.Neon indicators could easily be added to my circuit as well. It really was 5 AM.I tried to meet all the design considerations, both stated and implied.Quote from: 807 on May 03, 2023, 10:40:22 am

author: EPAIII
author_rank: Super Contributor
timestamp: May 04, 2023, 10:24:44 am
content: Strictly speaking, I suspect you are right. But somehow I think this guy is going to do this anyway and without the expense of running the power all the way across the river from one side only to switch it there and then run it back to the motor in the river. Also he is very likely going to do it without a licensed electrician, a permit, or any thought to having it inspected by a local code enforcement official.As for both contactors being energized at the same time, that is not possible with the circuit as drawn, except via manually activating the contacts on the unused one while the other one is activated. And then, if there was a mismatch in the phasing of the two power feeds, the weakest two fuses WOULD blow, almost instantly. This will happen even if they are grossly oversized. And I can almost positively guarantee you that the person who manually activated that contactor would both need clean underwear and would never even think of doing that again.Is your answer better?Yes, it positively is.Is this guy going to do it that way? I really doubt it. I really kind of doubt he will go for something as expensive as my circuit. What will probably get installed is something real cheap and possibly quite dangerous. But I will go on record here and now: I RECOMMEND YOUR CIRCUIT. STRONGLY! And I recommend that he do the proper calculations to find the proper size of the conductors needed for each branch of that circuit. And USE conductors of that size or larger.Happy?Quote from: james_s on May 03, 2023, 08:16:28 pm

author: EPAIII
author_rank: Super Contributor
timestamp: May 04, 2023, 10:28:55 am
content: One more point here: mechanically interlocked switches are NOT fool proof. I have seen some designs that could EASILY fail with both sides connected at the same time. Not all, but some. They are out there and probably still in use.