ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
Top Posters(30 Days)
twh 10
Recent Posts
Windows 10, who's upgraded?
by ElectricianBud. 05/27/17 11:02 AM
How do you find a good employee?
by ElectricianBud. 05/27/17 10:58 AM
Recall notice: Bosch Solar panels
by ElectricianBud. 05/27/17 10:53 AM
Correct rotation, wrong sequence
by Potseal. 05/27/17 12:15 AM
Dryer, Range grounding from "Main" panel
by sparkync. 05/25/17 05:49 PM
New in the Gallery:
SE cable question
Popular Topics(Views)
236,923 Are you busy
171,931 Re: Forum
164,813 Need opinion
Who's Online Now
0 registered members (), 45 guests, and 9 spiders.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate This Thread
#129063 - 07/08/04 10:45 PM +ve grounding  
luckyali  Offline
Junior Member
Joined: Jun 2004
Posts: 7
There are three grounding systems float,-ve and +ve.Now my question is that why +ve grounding is carried out and what are the advantages and disdavantages of +ve grounding as compare to other two system?

[This message has been edited by luckyali (edited 07-08-2004).]

Tools for Electricians:

#129064 - 07/09/04 11:17 AM Re: +ve grounding  
Bjarney  Offline
Joined: Apr 2002
Posts: 2,527
West-Southern Inner-Northeast ...
Don't think "ve" is an ANSI term. Would you please elaborate?

[This message has been edited by Bjarney (edited 07-11-2004).]

#129065 - 07/10/04 03:26 AM Re: +ve grounding  
luckyali  Offline
Junior Member
Joined: Jun 2004
Posts: 7
I mean that in DC system we ground the negative or positive or none of both,so my question was,why positive grounding carried out and what are the advantages and disadvantages as compare to others two?

#129066 - 07/10/04 12:39 PM Re: +ve grounding  
pauluk  Offline
Joined: Aug 2001
Posts: 7,520
Norfolk, England

"+ve" and "-ve" are commonly used abbreviations for positive and negative in parts of the world which came under British influence.

There are various reasons for adopting positive or negative grounding on DC systems, probably the most well-known one being the electrolytic action which can be set up, resulting in the erosion of conductive materials.

That's one reason why almost every telephone system in the world works with a DC supply which has the positive pole of the battery grounded.

When it comes to supplies for feeding certain electronic equipment, there is also the question of whether the primary devices used in the equipment require a supply line positive or negative with respect to earth.

From an historical viewpoint, valve/vacuum tubes operate with a positive supply line, and thus have a negative-ground supply, whereas much early transistor equipment used PNP transistors which required a negative line and thus a supply with its positive side grounded.

#129067 - 07/11/04 12:44 AM Re: +ve grounding  
luckyali  Offline
Junior Member
Joined: Jun 2004
Posts: 7
dear i mean that what is the reason to ground the positive?is there any special reason?if negative can be grounded then why we ground positive?

#129068 - 07/11/04 08:11 AM Re: +ve grounding  
winnie  Offline
Joined: Sep 2003
Posts: 649
boston, ma
I believe that pauluk gave the primary reasons for grounding the positive terminal on a DC system.

With respect to electronic equipment on DC supplies, I would like to expand a bit. Clear the supply to the devices requires both positive and negative, but especially with respect to 'three terminal devices' (vacuum tubes, transistors, etc) you see a useful asymmetry: The control signal to the device (gate drive, base drive, etc) is referenced to one of the terminals. If you ground that terminal, then the voltages associated with the gate drive are greatly reduced. For example, an N channel MOSFET is controlled by a gate voltage relative to the source terminal of a few volts, even for MOSFETS (or IGBTs) rated for drain to source voltages of thousands of volts. In circuits that use these devices, it generally makes sense to ground the source terminal. (Note that many interesting circuits use MOSFETS in ways where at least some devices can not be grounded.) Some devices connect the source lead to the metal body of the device; if the source lead is at ground potential, then you can ground your heat sinks, a very attractive design feature [Linked Image]

I believe that you left out one additional sort of grounding used in DC systems, at least in small signal circuits, and in large VSD DC links: neutral grounding, where you have +Ve and -Ve, and ground '0' in between the two. Common power supplies for things like op-amps are +-15V, and in most VSD systems you have a 'ungrounded' DC bus supplied by rectifying the supply AC...but the supply system is grounded, so the net result is a DC bus which is balanced about ground potential.


#129069 - 07/12/04 06:13 PM Re: +ve grounding  
pauluk  Offline
Joined: Aug 2001
Posts: 7,520
Norfolk, England
Good point about a balanced DC supply with grounded neutral Jon. The op-amp is an excellent example.

There are plenty of other electronic applications of DC with positive and negative (with respect to ground) supplies of vastly different levels.

In high-power tube transmitters, for example, it's quite common to need a supply with a positive (B+) line of hundreds or even thousands of volts, while at the same time you need a supply which is negative with respect to ground (C-) of maybe 30 to 100V (used for grid bias).

In DC power systems there are also examples of some strange unbalanced-about-ground systems.

The London Underground (subway system), for example, has a 630V DC supply using a four-rail system (two running rails, plus two completely separate and isolated conductor rails). Apparently they have the supply arranged so that the outer rail is at about +420V to ground and the central rail at -210V.

#129070 - 07/26/04 09:35 PM Re: +ve grounding  
dereckbc  Offline
Joined: Oct 2003
Posts: 156
Tulsa, OK
I can answer your question in more depth if you are still interested.

As Paul pointed out it has to do with electrolytic action. In the early days of telephone the outside plant cables were lead sheathed and referenced to the battery positive terminal (-48 VDC systems). This kept the lead from erroding and leaching into the soil.

On the other hand radio transmission (microwave/sat) equipment uses +24 VDC with the negative terminal referenced to ground.

These two schemes exist today. You are correct neither polarity has to be referenced to ground, but it is still done as to facilitate simple and econnomical overcurrent protection systems. Otherwise you would need to use ground fault protection/detection, and use shunt type breakers on each polarity in primary and secondary circuits for protection. Hope that helps.

Member Spotlight
Posts: 47
Joined: March 2008
Show All Member Profiles 

2017 NEC and Related
2017 NEC
Now Available!

Shout Box
Powered by UBB.threads™ PHP Forum Software 7.6.0
Page Time: 0.017s Queries: 14 (0.002s) Memory: 0.7944 MB (Peak: 0.9516 MB) Zlib enabled. Server Time: 2017-05-28 08:34:47 UTC