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IT Network

IT Network

IT Network

(OP)
Hi forum members,

I need a clarification about the IT network.The neutral is not grounded and this network is only allowed for three phases load.For single phase load, a delta/star transformer is used to provide the neutral.At a place of work, I noted that this neutral is not grounded.I belive this is a violation of the code as the neutral is no longer at earth potential.

Guardiano

RE: IT Network

Do you mean you think that an IT system is a code violation? I guess that depends on which code you mean. It is permitted in Europe, but it is relatively unusual and needs specific precautions.
  

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If we learn from our mistakes I'm getting a great education!
 

RE: IT Network

You are saying this is an Information Technology, (IT), network?  I assume you are talking about the power system that supports the network.  Whether it is or not should not make a difference to the power system feeding it if the star point of a delta-wye transformer is not grounded.  It must be grounded or it is a code violation no matter where you are if the neutral is utilized on the secondary side for single phase load connections.

RE: IT Network

In North America, when the IT people started using ground return comm links back in the 60's they made a few erroneous assumptions regarding the grounding methods and reliability of commercial wiring. They were installing comm links for cash registers in buildings that were old and may have been wired before grounding became a requirement. Also, grounding methods in the 40's and 50's left much to be desired and were often not a reliable return path for data signals. Note; In their ignorance of methods and codes they violated the existing code rules that said that no device may depend on a ground connection for proper operation. There were exceptions that did not apply to data links.
The data people came up with grounding schemes to address unreliable grounding systems. At the same time, codes were changing and modern ground methods became as dependable and reliable as the "Special grounds".

Quote:

The neutral is not grounded and this network is only allowed for three phases load.
What is the voltage. If a neutral point is available that will limit the maximum nominal voltage to ground to less than 150V then the system must be grounded. If the system is not grounded, all equipment must be capable of withstanding phase to phase voltage applied phase to ground. Not all equipment is suitable for use on floating systems. Blown front ends on rectifiers and other equipment may result from a remote ground fault.

Quote:

I belive this is a violation of the code as the neutral is no longer at earth potential.
Another North American code violation. If a neutral is used for line to neutral loads the neutral must be grounded.
In North America it is common for IT to install a dedicated ground bus for all it grounding. Then, the electrical contractor connects this bus to the main building/system ground bus with a 4/0 copper cable to satisfy code requirements.
I always laugh when I see a magic triangle being installed. This is three 3M ground rods in a 3M equilateral triangle. The grounding system in an industrial may entail 1000 times the weight of the "magic triangle" of copper cables. There is actually a danger that a massive ground fault, on its way to the main ground grid may, cause an elevated ground potential on the IT network. However, if the installation is up to code there will be a large ground cable connecting the magic triangle to the main ground grid and thus saving the it people and equipment from harm. We have learned to not waste time arguing with IT guys. They seem to have a contempt for anyone working with power frequencies, currents and voltages and can not possibly learn anything new. They know Ohm's law, what more is there to power systems?
We quietly install the jumpers to bring the system up to code and make it safe and avoid confrontation. If you make a big deal out of connecting the IT ground to the system ground, the ITs may disconnect it after you have left.
Install the proper grounding quietly and what they don't know may save their lives and/or equipment.
 

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: IT Network

That's a nice link, David.
While I was on the Information Technology soapbox, the OP may have intended the European IT or floating neutral systems.
And I was on a roll!
LPS for the link and my further education.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: IT Network

Thanks, Bill.  Maybe one of these days, I'll get around to actually reading it. looking around
 

David Castor
www.cvoes.com

RE: IT Network

(OP)
Got the points.My concern is that many sensitive electronic equipment on site are not designed to withstand the phase-phase voltage on the occurence of a first fault(phase-ground).I intend to use a transformer and convert the IT to a TT network for the electronic equipment.I am looking for possible safety hazards in doing so.
Guardiano

RE: IT Network

With the addition of the transformer you would (I think) have a TN-S system with the transformer secondary as the origin and not a TT system. TT systems have an earthing electrode remote from the earthing electrode of the system neutral, whereas you will earth your neutral at the transformer and presumably take a separate neutral and earth conductor from that point.

I can see a possible 'safety problem' caused by the relatively high source impedance and the low fault level which will potentially cause difficulties with fault clearance times. That shouldn't be anything which can't be dealt with using normal methods, e.g. RCD or RCBO. Another safety problem may occur if you have supplies from both systems in the same area, especially if some helpful soul decided to bond the neutrals or use a convenient neutral from one service and a convenient phase from the other service to power a load. Bad workmanship for sure, but that doesn't mean it can't happen.

Is the isolating transformer a Y-Y type or a DY?
  

----------------------------------
  
If we learn from our mistakes I'm getting a great education!
 

RE: IT Network

(OP)
Thanks scottyuk for your pertinent comments.Agree for the TN-S system.The transformer is basically a 400 V(P-P)/230 V (PN) one.Also agree with you about the special caution as regards the bad workmanship.
Guardiano

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