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Started by Chris Elston10 Oct Posted 10 Oct Posted 13 Oct Posted 14 Oct Posted 15 Oct Posted 20 Oct Posted 23 Oct Posted 30 Jan Posted 20 Mar Posted 20 Apr Posted 24 Apr Posted 25 Apr Posted 5 May If I rem correctly it is required by the NEC to always ground the secondary on any power supply or transformer volts and below.
My old boss who slept with the NEC code book under his pillow Jim Grace stressed this point with me back in the day. Posted 28 Mar edited. Posted 11 Apr So I was wondering what other people do Do you ground your 24VDC common of your power supply to earth ground as well as run a common wire out? Just curious what other people do and why? Would you if you had analog devices? Would you if you had cheap VFDs? You need to be a member in order to leave a comment. Sign up for a new account in our community.
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Back in the day when we all used linear power supplies, the common was always grounded. Since we've moved on to switch mode power supplies, we always leave the common ungrounded, with a switched power supply you have true isolation.
I have not grounded the common in many years, since I work at a chemical plant, we use a LOT of analog devices, I've never had an issue. If I remember correctly, we made the switch when we quit using ExP devices and went to Intrinsically Safe Devices, some of the barriers required ungrounded DC systems.
However, we do not have any cheap VFD's, might have a few of questionable quality, but they were not cheap but if you use good wiring practices, then noise is almost never an issue anyway. Agree with Ken whole heartedly One of the dumbest things I saw was an AC neutral ran into the common input for the DC SINK module, and they wondered why it did not work, Gender Graphic Venerator - Ken Moore - Frame Of Reference why the inputs indicators were constantly dimming and not working.
And yes a negative voltage was a logical "1". Talk about my world turning upside down when I went to work for one of old Henry Fords suppliear and entered the AB world. If I were to ground anything now it would be the Speaking of cheap VFDs I had an old EMS drive die recently. Yeah, it was possible thru programming on both drive types!
My next quest What's that all about? Either the power supply does not have internal power protection rare these days or they simply added a voltage deregulator! The PSU has long since been changed for a switchmode. It is quite a good reference document for noise considerations when designing electrical systems. I always ground the DC power supply for two reasons: 1 Safety - Most people think of 24VDC as safe including myself and have no problem touching anything with 24V.
Now lets say, the common is not grounded and some where in the circuit a DC Cmmon wire comes in Instrumental - Bob Dylan - Never Ending Tour Rehearsals with a high voltage like V, a fuse will not blow nor a breaker trip.
In Cotnrols DC it makes a lot of sense to ground the 24 - for the reasons listed. In Instrumentation DC there are an equal number of arguments isolation, noise, cross-talk for not grounding either side of a 24 vdc supply. Why would grounding the common attenuate noise? If I have an isolated 24VDC power supply I can only see grounding the common as introducing noise into the system.
We have our unit installed at a factory that reads our signal with an Analog input module. Does anyone have experience with this? What about when you have both in the same cabinet? We've had issues where level switches would not act right until the power supply was grounded, plus we had analog signals being fed off the same power supply. On this case we had to isolate the ground buss that the shields and power supply ground were going to from the equipment ground.
Let me offer my 2 cents. When you install this ps in a panel this voltage shifts depending on the impedances of the circuit. If you unground this power supply then you run a risk of exceeding the common mode voltage limitations of analog circuits.
If you ground this power supply then you are attenuating this common voltage problem by keeping the dc- of the supply at the machine ground potential. This can cause a problem with small signal millivolt measurements. What I Gender Graphic Venerator - Ken Moore - Frame Of Reference been doing is using a linear supply for analog and a switching supply for control.
I know this is controversial in some circles but if the measurements are critical then this is the solution I have found to be the most effective. I have a machine I was Niemals Real - Various - Deine Mutter Ein Tape.
Vol. 1 on today that we decided to remove the switchmode supply and run only a linear supply. The linear supply has more heat gerneration due to the lack of efficiency but it is the superior solution given the requirements. The majority of installations will work fine with switching supplies. In answering your question: Linear supplies: ungrounded Switching supplies: grounded.
The battery supply negative is grounded - it supplies the hard wired stuff and generator controllers. Battery chargers can go high, surges damage the PLC etc. The switch mode affords protection to the PLC but if the negative is grounded there is no isolation between one side of the switch mode and the other.
May as well Ο Παράδεισος Πουλιέται Με Το Τετραγωνικό - Νίκος Καρβέλας - Τρακτέρ use one.
Point well taken! I was addressing a typical manufacturing environment. However, we also have battery operated equipment with Gender Graphic Venerator - Ken Moore - Frame Of Reference . These systems are all isolated from the frame including the battery. In your case with a generator you have to deal with a whole host of issues most of us are lucky enough to avoid. For the benefit of other readers here, be careful when selecting a power supply when isolation is needed.
Not all supplies provide this and simply not grounding one of the outputs does not give you isolation from the inputs. Gender Graphic Venerator - Ken Moore - Frame Of Reference transformer supplies have isolation issues. If all you need is DC isolation then most transformer supplies will suffice.
If you need AC isolation then look into ferro-resonant supplies. They are more expensive but if the application requires it they are a good solution. One other thing I might add with respect to not grounding the negative to a PLC - NPN inputs - grounding an input wire in the field can turn the input on - if it is not grounded there is no ground reference and the input will not inadvertently turn on. Typically found on Japanese machines. Usually use NPN outputs. Interesting stuff, I have recently been looking into this.
Edited 11 Apr by spitzy. Create an account or Air: Lentement - Wilhelm Furtwängler, Berliner Philharmoniker, RIAS Symphonie-Orchester Berlin - Edi in to comment You need to be a member in order to leave Gender Graphic Venerator - Ken Moore - Frame Of Reference comment Create an account Sign up for a new account in our community.
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