Posted 19 Jun 2014 (edited) Hi, there. I have a question about an electric wiring such as the attachment. There is some problem at the pointed connection between AC voltage and DC voltage in my mind. Can you explain about that? Thanks for your help in advance. Edited 19 Jun 2014 by Tom749 Share this post Link to post Share on other sites
Posted 19 Jun 2014 Need more information. What is the problem in your mind? There should only be DC voltage at that connection. With the negative lead of your meter on that point, and the positive lead at any point of the positive DC supply, you should see voltage. Share this post Link to post Share on other sites
Posted 19 Jun 2014 (edited) Short answer: you can do that, and it will work. I've seen it done. Slightly shorter answer: it's a stupid idea, and while it will work, point 3 mentions that you can power it with 24VDC as well. So you'd be far better off to do that. Long answer: in most cases, the neutral on the 24V side of your transformer is grounded/earthed, and so is the negative on your 24VDC power supply. So really, most of the time, thhose two points are already connected through the grounding system. Making an extra connection there won't make any real difference. But it's still a stupid idea. (Side note: not sure an Allen-Bradley PLC forum is the best place to post this. But hopefully you've got the answer you needed anyway ) Edited 19 Jun 2014 by ASForrest Share this post Link to post Share on other sites
Posted 19 Jun 2014 In addition to ASForrest, it doesn't look like there is any grounding on the common line. This could cause the common to be floating slightly. Using a multimeter/voltmeter, test between common and your ground/earth on both AC and DC, just for good measure. If above about 2 volts, there may be a problem somewhere. It should be less than 1 volt. If less than 2 volts, just link your common to ground/earth to stop any floating voltage on the common. This should sort it out, but as said, a 24VDC supply would be the better, safer option. Share this post Link to post Share on other sites
Posted 8 Jul 2014 very common for AC and DC to share ground when building control panels, just more so in the control panel and not out in the field like this drawing is showing. Share this post Link to post Share on other sites
Posted 8 Jul 2014 It seems odd that 1 is common and 2 is hot. Seems like it should be the other way around, but for some reason that's the way they numbered it. Share this post Link to post Share on other sites
Posted 8 Jul 2014 Well everything else about it is backwards, why stop there? ;) Share this post Link to post Share on other sites
Posted 9 Jul 2014 It's just a make shift power supply. If you look at the internal schematics of a power supply that's how they work. The dc common is referenced by the ac neutral. That is why it is good practice to tie the common to ground as well as your ac neutral can float around a bit. Share this post Link to post Share on other sites