Is it a good idea to connect the Negative (Black) of a DC PSU to the ground point in a control panel where the GND (Green or Copper wire) from the 120VAC is connected?
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Is it a good idea to connect the Negative (Black) of a DC PSU to the ground point in a control panel where the GND (Green or Copper wire) from the 120VAC is connected?
Ground is ground. It does not matter what the voltage is. Nothing will travel through ground to other components if that's what you are worried about. It will only send the voltage to ground and possibly trip a breaker or blow a fuse. But that tends to happen when you ground out any voltage.
I usually earth ground P.S.'s commons where possible, The only time rare time it can cause a problem is in a linear P.S. that has a winding of the secondary connected to ground, if you GND the DC common, then it creates a short through the rectifiers.
Al..
Somehow I didn’t like mixing up grounds from AC and DC. Now I understand
Thanks
It should be done with a central or star ground point,that includes the service ground, I use either a copper plate drilled and tapped or a the green/yellow DIN style Earth terminals that automatically connect to ground.
Al.
I have been using a 1/8” thick aluminum plate approx. 3”x3” as my star ground point which includes the service ground as per attached picture. However in this case the negatives from my PSU are not included on this ground point.
Next time I will include the negative from the PSU plus I will use the DIN style Earth terminals which makes an easier and much better looking installation.
You have been an excellent teacher Al, thank you
You are NOT suggesting to connect the safety ground ( typically the green wire) to some point within your power supply system are you? The purpose of this wire is to ground any part of the chassis or case that might come in contact with a human being to protect against the chassis be coming "live". Electrically speaking: the neutral wire and the safety ground wire are connected to the same point back at your breaker box. And that is the only place they should be connected.
I'm not suggesting that; what I'm saying I will only connect the 120VAC green wire (or bare copper in some cases) to a star point in my control panel and at the same point I will connect only the negative (Black wire) from the PSU. Inside my house main entry electrical panel I think the white wires are all connected to one bar and the bare copper wires (ground) are connected into another barQuote:
Originally Posted by WoodWorkerB
Should really be a Single Point, but what you have done not ideal but should work ok, if you are running a VFD and your DC supply is feeding electronics, leave the Negative floatingQuote:
Originally Posted by kolias
Not a big deal mastec54 to do my star point like you indicate however I do plan soon to get a VFD and in that case what do you mean “leave the Negative floating”?
Perhaps it means not to connect the PSU Negative to the star point?
There are two schools of thought on P.S. common grounding, if it is electrically possible I have always grounded the DC common, your PC P.S. has this done already inside the PC unless it is a Laptop.
No need to go back to the panel for this, I am talking machine enclosure wiring.
There are several threads here where noise problems were solved after using the P.S. grounding technique.
Al.
When using a VFD in the system they are very noisy, they are Grounded, Both the VFD and the Motor/Spindle, the Ground will have a lot of nasty spikes and voltage, that can mess up your DC supply if it is included with your star GroundQuote:
Originally Posted by kolias
Your Power supply's are Grounded, and Isolated some have double Isolation, so have no problem not being part of the Ac 120/240v supply, Yes it's called floating in a good way, when not connected to Star Ground
I agree with Al with what he is saying, but when you add a VFD to the System that is when you can have problems with what is called Common Mode Voltage ( CMV ) this will occur on all VFD driven Motors and is really bad the higher the Frequency goes, 50Hz 60Hz not to bad, and is easy to deal with, the Spindles you will be running are 300Hz and 400Hz so create lots of noise on the VFD and Motor Ground, that can/will feed back into the DC supply if it is connected
The latest VFD Drives there switching frequency is higher than it used to be, creating even more Common Mode Voltage in the driven Motors, this all goes to Ground
See http://www.cnczone.com/forums/phase-...se-issues.htmlQuote:
Originally Posted by kolias
Particularly post #9.
Al.
Very informative thread AlQuote:
Originally Posted by Al_The_Man
Thank you
That shows what should have been done, from the start, this shows you a perfect example when the DC Common should be Grounded, the drives he is using dictate that this would be neededQuote:
Originally Posted by kolias
The ground wire sends the voltage back to the source not to ground. Unless we are talking about a lightning strike.Quote:
Originally Posted by bsm2003
Do you mean it returns to the electrical source via a grounded conductor? It does not truly travel to earth, unless the spike was lightning.Quote:
Originally Posted by mactec54
A Grounding conductor is for safety should never be used for anything else other than a safety GroundQuote:
Originally Posted by MML102783
No when using a dc power supply you have a + positive and a - Negative ( Common ) a dc Power supply the Common must return to the ( source ) dc supply to complete the circuit, then it can be Grounded to Earth Ground conductor in special circumstances, dc supplies are Grounded normally with the input AC power supply
There are some people that connect the dc common direct to Earth Ground, when using a dc supply this can cause problems even though they say it does not, the main problem is noise on the Ac Earth Ground which can affect the low voltage dc supply
In the case of a lightning spike connected this way could take out all the low voltage components
The AC service supply has a grounded neutral at the supply transformer, so any power conductor connected to this supply is referenced to earth ground, which means that any current connection/leakage of the power conductor to earth results in a electrical circuit back to the source, i.e. through ground to the earthed supply point.Quote:
Originally Posted by MML102783
Once upon a time, rural telephone systems used the ground for the return path in order to save cost of using two conductors.
Any isolated supply that you chose to make one side common to earth ground uses the same return path to the grounded conductor source.
I have made it a practice throughout my career to earth ground all supply systems whether AC or DC, with no ill effects.
There have been a few past posts here where those that have had spurious e-stops problems have cured the issue by grounding the power common
A -ve charged lightening storm cloud has a equally +ve charged area in the ground that follows the storm cloud as it travels.
Good PDF but very old publication Note it states that the common of a DC supply must return to the source, it can then go to Ground if you chose, not to have the DC supply floating, your method is problematic, if you have a VFD Drive in the same system as Ground then has a lot of noise which will mess with the low voltage system, and all most everyone use's a VFD Drive in there systemQuote:
Originally Posted by Al_The_Man
Installed many systems earth grounding the DC supplies common and have not had a problem, I set up a 1/4" tapped copper ground plate and take every earthed common to it.
Together with equi-potential bonding.
Per the PDF: The concept of Earth consists of one homogeneous mass that is electrically neutral, i.e.
an equal number of negative and positive charges are distributed throughout the earth at any given time.
And how many Hobby user's can achieve this here on the Zone, you are talking a foreign language to a Hobby user, which only ends up with more problems, when they try and achieve a system that has an equi-patential bonded Ground system, what you did in the industry does not equal Hobby user, this is for dreamers only, you have been here long enough to know thatQuote:
Originally Posted by Al_The_Man
There is nothing complicated actually. Only the problem is the way of explanation. It depends on the level of understanding and education background. Up to now the best description of "grounding" and protective earth belongs to Siemens in my opinion. I recommend to learn. Covers almost all aspects of earthing, Very detailed.
Contains no expressions like "returning to source" or so.
If you are talking about Ac Power Earth Ground circuits then that would be correct, you are not going to find source being used in an Ac circuit, understand what is being discussed would help you understand why the word source is usedQuote:
Originally Posted by Algirdas
Agree!Quote:
Originally Posted by Algirdas
Good comment!