Neutral Grounding - at More than one place - Exceptions

[jeganathan]

It is required to ground the grounded terminal (neutral) at the utility side(sub control panel) to improve EMC.

Is there any exception in the Standard to allow this additional grounding.

 

[bphgravity]

Re: Neutral Grounding - at More than one place - Exceptions

Excuse my ignorance, but what is a "sub control panel" and the term "EMC"?

 

[jwelectric]

Re: Neutral Grounding - at More than one place - Exceptions

Let me dissect this question.

It is required to ground the grounded terminal (neutral) at the utility side
We must always bond the grounded (neutral) and the grounding electrode on the utility side of the service. 250.24 (D)

Is there any exception in the Standard to allow this additional grounding.
The only other place that this is allowed is outlined in 250.30, 250.32 and 250.34

Now that I have made an attempt to answer you would you please do the same for me and answer this.

Originally posted by bphgravity:
Excuse my ignorance, but what is a "sub control panel" and the term "EMC"?

 

[charlie b]

Re: Neutral Grounding - at More than one place - Exceptions

"EMC" would be "Electro-Magnetic Compatibility." It is a broader term that is in the process of replacing the older "Radio Frequency Interference" (RFI), as a criterion for evaluating the impact of one item of equipment on another. I suspect that "Sub Control Panel" is merely an imprecise, conversational phrase for some connection point within the substation.

 

[jeganathan]

Re: Neutral Grounding - at More than one place - Exceptions

Sub Control Panel (SCP) is nothing but a local power and control distribution panel having its own control system for local and descrete operation and interface to Plant for Integrated control sytem.

Does NEC allow muliple grounding of neutral for voltages less than 150V (between phase and ground)? for industrial application?

Which article of NEC permits connection of Neutral to PE at the load side for industrial application?

 

[roger]

Re: Neutral Grounding - at More than one place - Exceptions

Originally posted by jeganathan:


Does NEC allow muliple grounding of neutral for voltages less than 150V (between phase and ground)? for industrial application?

Only ahead of the main.

Why would you want to create these parallels and/or loops anyways?


Roger

 

[jeganathan]

Re: Neutral Grounding - at More than one place - Exceptions

Connecting Neutral to the PE at the Local Panel to improve EMC i.e, to reduce noise in terminals. Communication and IT equipments use 0V reference and this requires a practical 0V between Neutral and Ground.

 

[roger]

Re: Neutral Grounding - at More than one place - Exceptions

Then you need to treat your installation as an Isolated Ground and take all your additional grounding back to the MDP, you can not ground to the neutral at more than one location.

I can't see how creating these loops will reduce noise or dirt, it seems to me with the net currents you will have flowing you will actually magnify the problem.

Roger

 

[justdavemamm]

Re: Neutral Grounding - at More than one place - Exceptions

Originally posted by jeganathan:
Connecting Neutral to the PE at the Local Panel to improve EMC i.e, to reduce noise in terminals. Communication and IT equipments use 0V reference and this requires a practical 0V between Neutral and Ground.

The neutral you speak of, I am thinking, is either on the secondary of a transformer, thus required to be grounded, or the return path of a DC Power supply. Quite different than what I presume that most people here are thinking you are asking about. ICBW.

As a side note, most communications signals that are going any distance are differential in nature and neither wire is grounded.

 

[iwire]

Re: Neutral Grounding - at More than one place - Exceptions

jeganathan there is no code compliant way to re-ground the neutral to the ground on any branch circuit.

The fact that you are contemplating it suggests you have not thought this action through.

Draw the distribution system in the normal fashion then add your modification.

What you will see is that you have created countless parallel paths for the current of all the buildings circuits through your added connection.

This will cause high magnetic fields and more problems then it can ever solve.

If you have already decided this issue of the neutral and ground having a difference of potential must be eliminated your only option is to do what Roger said and run an isolated grounding conductor back to the power source. This isolated grounding conductor must be run in the same cable or raceways that feed the circuit.

Personally I think your chasing the wrong problem.

[ September 16, 2005, 09:14 AM: Message edited by: iwire ]

 

[bassphisher]

Re: Neutral Grounding - at More than one place - Exceptions

Sounds to me like you are having problems with harmonics,and need to do some research in that area.I believe one of the basic tests to see if you have a harmonic problem is to measure the voltage between neutral and ground at one of the farthest outlets.Have you done this,If so how many volts did you measure?
Paul Electrical Inspector

[ September 16, 2005, 09:58 AM: Message edited by: bassphisher ]