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Post by TonyDunkley on Feb 28, 2019 22:44:51 GMT
that applies to you ..... a knobhead through and through ..... don't throw your idiot advice in because you don't like Tony ....... all you do is muddy the waters, read what the op posted and think what could happen Imagine the following. We have a 12v battery, a 12v lamp, and two lengths of wire. We connect the 12v lamp to the 12v battery using the two lengths of wire. It illuminates. We now cut the feed wire (or the return wire, it really doesn't matter) and place an on/off switch in the circuit. Oh, I do hope you've got your boat wired up with some of the switching in the negative (return) side of your various DC circuits, . . and I hope someone is there to take a photo of it when it goes up in flames !
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Post by JohnV on Feb 28, 2019 22:51:59 GMT
you really are a dip shit ..... it is a double pole switch it switches both positive and negative It doesn’t have to. And no point in breaking the negative wire just to pass it through the switch. correct but that is changing what was asked advice was requested on using a particular switch and switching both is not a bad idea redesigning what was asked is fine but the main need is not to assume the person asking the question has technical knowledge. You go along with his intentions as long as they make sense.. <iframe width="24.299999999999955" height="4.840000000000003" style="position: absolute; width: 24.299999999999955px; height: 4.840000000000003px; z-index: -9999; border-style: none;left: 15px; top: -5px;" id="MoatPxIOPT0_74968606" scrolling="no"></iframe> <iframe width="24.299999999999955" height="4.840000000000003" style="position: absolute; width: 24.3px; height: 4.84px; z-index: -9999; border-style: none; left: 1290px; top: -5px;" id="MoatPxIOPT0_35371899" scrolling="no"></iframe> <iframe width="24.299999999999955" height="4.840000000000003" style="position: absolute; width: 24.3px; height: 4.84px; z-index: -9999; border-style: none; left: 15px; top: 183px;" id="MoatPxIOPT0_4764162" scrolling="no"></iframe> <iframe width="24.299999999999955" height="4.840000000000003" style="position: absolute; width: 24.3px; height: 4.84px; z-index: -9999; border-style: none; left: 1290px; top: 183px;" id="MoatPxIOPT0_40702810" scrolling="no"></iframe> coming out with the crap that mr stabby did, just confuses the issue especially as it was purely about trying to point score off Tony and not about ensuring the op did the safest thing
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Post by JohnV on Feb 28, 2019 22:57:09 GMT
On the safety aspect Welly ....... I trust you are coming from a 12v supply that has a small value fuse in it ...... if not I suggest you put one in the circuit
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Post by Telemachus on Feb 28, 2019 22:57:38 GMT
Imagine the following. We have a 12v battery, a 12v lamp, and two lengths of wire. We connect the 12v lamp to the 12v battery using the two lengths of wire. It illuminates. We now cut the feed wire (or the return wire, it really doesn't matter) and place an on/off switch in the circuit. Oh, I do hope you've got your boat wired up with some of the switching in the negative (return) side of your various DC circuits, . . and I hope someone is there to take a photo of it when it goes up in flames ! Why would it go up in flames just because the switch is in the -ve? Does a switch in the positive side automatically open when there is a fault, and the boat’s occupant is doing a dump in the loo? Or do we have fuses in the positive supply for that purpose? Stick to what you know Tony. On this topic, you resemble NaughtyCal giving advice on the Trent. <harsh but fair!>
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Post by Telemachus on Feb 28, 2019 23:05:41 GMT
It doesn’t have to. And no point in breaking the negative wire just to pass it through the switch. correct but that is changing what was asked advice was requested on using a particular switch and switching both is not a bad idea It is a bad idea, because it is unnecessary, gives no benefits, introduces an additional failure mode and voltage drop. Just because a switch is double pole doesn’t mean one has to use both poles. It is not changing what was asked. You misread the question.
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Post by TonyDunkley on Feb 28, 2019 23:10:32 GMT
Oh, I do hope you've got your boat wired up with some of the switching in the negative (return) side of your various DC circuits, . . and I hope someone is there to take a photo of it when it goes up in flames ! Why would it go up in flames just because the switch is in the -ve? Does a switch in the positive side automatically open when there is a fault, and the boat’s occupant is doing a dump in the loo? Or do we have fuses in the positive supply for that purpose? You're talking nonsense, Nick, and I think you know you are. I'd always regarded you as a giver of sound advice on matters electrical, . . . but apparently not. Do you really believe that switching in DC circuits which leaves components and/or any electrical gadgets with a 'live' feed when they're supposed to be switched off is good, safe practice ?
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Post by JohnV on Feb 28, 2019 23:14:59 GMT
you are assuming that he is cutting into the supply cord to the unit which I suspect he is not ...... If he has bought a wall mounted switch plate it is fair to assume that he will be wiring positive and negative installation cables, either from another circuit or from the fuse panel to that switch. He will therefore have to attach both negative and positive wires at that point. Therefore you might as well use both sides of the switch .... I would suggest better than putting both the negative boat wiring cable and the supply cord into the same screwed connection
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Post by Telemachus on Feb 28, 2019 23:20:38 GMT
Why would it go up in flames just because the switch is in the -ve? Does a switch in the positive side automatically open when there is a fault, and the boat’s occupant is doing a dump in the loo? Or do we have fuses in the positive supply for that purpose? You're talking nonsense, Nick, and I think you know you are. I'd always regarded you as a giver of sound advice on matters electrical, . . . but apparently not. Do you really believe that switching in DC circuits which leaves components and/or any electrical gadgets with a 'live' feed when they're supposed to be switched off is good, safe practice ? Given the choice of course I would switch the positive. Which is what I told the OP in an earlier post. But it doesn’t much matter. You use the words “good” and “safe” adjacently to describe “practice”, as if they were the same thing. Which they aren’t. A switch in a 12v system doesn’t provide “safety”. That is provided by suitable fusing. It is of course normal, and hence good, practice to switch the positive, but not for reasons of safety. To claim otherwise is to over-egg and thus lose the argument. Where there is a risk of electric shock, of course the arguments are entirely different. But it is pretty hard to get a dangerous shock from 12v unless you are in the habit of, say, poking electrodes up you jaxxi.
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Post by Andyberg on Feb 28, 2019 23:26:59 GMT
Just to play Devils Advocate & add further confusion here. 👍 😂
Every install I have completed at work has been switched - Negative Feed with + Positive being the Mid (Return ) point!
Served me well for last 31 years! 👍
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Post by Telemachus on Feb 28, 2019 23:30:57 GMT
you are assuming that he is cutting into the supply cord to the unit which I suspect he is not ...... If he has bought a wall mounted switch plate it is fair to assume that he will be wiring positive and negative installation cables, either from another circuit or from the fuse panel to that switch. He will therefore have to attach both negative and positive wires at that point. Therefore you might as well use both sides of the switch .... I would suggest better than putting both the negative boat wiring cable and the supply cord into the same screwed connection I would suggest that a 20A switch has quite big screw connections. Have you ever poked a small wire designed for 1A, into a large screw connection designed for 20A, tightened it up and then found that the screw has entirely missed the wire, which can then easily be pulled out? In which case, sharing one connection with 2 wires (thus making it fatter) might be a better idea. Although admittedly the problem might recur on the positive side! Anyway, we don’t know where the connection between the router’s cable and the switch will be. Will the router be connected directly to the switch, or will it be more remote with additional wire? Who knows. The important point is that there is nothing electrically beneficial in using both poles, and some minor disadvantage. It may or may not be physically convenient to use the second pole as a physical connector.
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Post by JohnV on Feb 28, 2019 23:33:08 GMT
Just to play Devils Advocate & add further confusion here. 👍 😂 Every install I have completed at work has been switched - Negative Feed with + Positive being the Mid (Return ) point! Served me well for last 31 years! 👍 hope you didn't wire your boat like that ...... could prove interesting for the next owner if you sell it
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Deleted
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Post by Deleted on Feb 28, 2019 23:35:56 GMT
I'm trying to fit a switch to turn on/off my 4g modem/router and have been struggling to find a wall switch that is specifically for 12v. Midland Chandlers has this www.midlandchandlers.co.uk/store/product/vs-215.aspx which suggests it works with 240v as well. I've just picked up a 240v 20a switch from screwfix and wondering if there's any reason why it wouldn't work with my router? The router requires 12v, 1a supply. Any thoughts? Cheers! Sorry if this is a daft question but hasn’t the router got it’s own on/off switch? Why do you need a separate switch?
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Post by JohnV on Feb 28, 2019 23:36:21 GMT
you are assuming that he is cutting into the supply cord to the unit which I suspect he is not ...... If he has bought a wall mounted switch plate it is fair to assume that he will be wiring positive and negative installation cables, either from another circuit or from the fuse panel to that switch. He will therefore have to attach both negative and positive wires at that point. Therefore you might as well use both sides of the switch .... I would suggest better than putting both the negative boat wiring cable and the supply cord into the same screwed connection I would suggest that a 20A switch has quite big screw connections. Have you ever poked a small wire designed for 1A, into a large screw connection designed for 20A, tightened it up and then found that the screw has entirely missed the wire, which can then easily be pulled out? In which case, sharing one connection with 2 wires (thus making it fatter) might be a better idea. Although admittedly the problem might recur on the positive side! Anyway, we don’t know where the connection between the router’s cable and the switch will be. Will the router be connected directly to the switch, or will it be more remote with additional wire? Who knows. But anyway the important point is that there is nothing electrically beneficial in using both poles, and some minor disadvantage. It may or may not be physically convenient to use the second pole as a physical connector. we could continue this almost ad infinitum but it would end up looking like a CWDF technical thread (thinks ...... shall I mention bootlace ferrules and the latest regs )
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Post by Deleted on Feb 28, 2019 23:37:46 GMT
My curiosity got the better of me.
Positive from the boat into Live in. Negative from the boat into Neutral in.
Live out from the switch into Positive in on the router Neutral out from the switch into Negative in on the router.
Flicked on the switch. All the lights went out. Flicked off the switch. All the lights came back on.
Weird. Note that this cable is routed into the lighting circuit. Not sure what would have caused that. Without the switch, it's been working hunky dory.
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Post by TonyDunkley on Feb 28, 2019 23:38:11 GMT
you are assuming that he is cutting into the supply cord to the unit which I suspect he is not ...... If he has bought a wall mounted switch plate it is fair to assume that he will be wiring positive and negative installation cables, either from another circuit or from the fuse panel to that switch. He will therefore have to attach both negative and positive wires at that point. Therefore you might as well use both sides of the switch .... I would suggest better than putting both the negative boat wiring cable and the supply cord into the same screwed connection I would suggest that a 20A switch has quite big screw connections. Have you ever poked a small wire designed for 1A, into a large screw connection designed for 20A, tightened it up and then found that the screw has entirely missed the wire, which can then easily be pulled out? In which case, sharing one connection with 2 wires (thus making it fatter) might be a better idea. Although admittedly the problem might recur on the positive side! Anyway, we don’t know where the connection between the router’s cable and the switch will be. Will the router be connected directly to the switch, or will it be more remote with additional wire? Who knows. But anyway the important point is that there is nothing electrically beneficial in using both poles, and some minor disadvantage. It may or may not be physically convenient to use the second pole as a physical connector. Aahh, . . shut-up Nick, . . vapouring old fart !
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