×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Tension between neutral and ground
2

Tension between neutral and ground

Tension between neutral and ground

(OP)
Hi!
Does anyone knows what is the maxim allowed tension between ground and the neutral in a TT system??
Thanks in advance
Martin

RE: Tension between neutral and ground

In which country?

----------------------------------
  I don't suffer from insanity. I enjoy it...

RE: Tension between neutral and ground

What do you mean by a TT system?
respectfully

RE: Tension between neutral and ground

TT = Terre - Terre. Describing a system where system is grounded at transformer (the first T) and housing separately grounded at load (second T).

It does not say if Neutral or one corner of the system is grounded at transformer (both are allowed).

So the question is not quite clear. You probably mean between load neutral and ground?

Gunnar Englund
www.gke.org

RE: Tension between neutral and ground

Hi waross,

It's European terminology. TT is an abbreviation for Terra-Terra. The source is grounded to a local earthing electrode or mat. The customer has a similar electrode at the service intake and there is no metallic ground connection between customer and source. Earth loop impedances are typically high and require use of an RCD as the intake switching device.

Other related European terms are:
  1. IT (Isolated-Terra) for ungrounded sources with an earth electrode at the customer intake.
  2. TNC (Terra-Neutral Combined) for a metallic combined earth and neutral conductor connected to an earthing elctrode at the source.
  3. TNS (Terra Neutral Separate) for a metallic earth conductor, separate from neutral, connected to an earthing elctrode at the source.
  4. TNC-S (Terra Neutral Combined-Separate) for a combined neutral and earth up to service entrance connected to an earthing elctrode at the source, with separate neutral and earth conductors available at the customer's intake.
TNC-S is frequently seen in the UK as Protective Multiple Earthing or PME. PME allows the distribution company to effectively earth the neutral conductor throughout its length as well as at the substation earth mat, saving the cost of running a separate earth conductor.

----------------------------------
  I don't suffer from insanity. I enjoy it...

RE: Tension between neutral and ground

(OP)
Thanks to all of you!
I need the maxim allowed tension between the neutral (in the load) and the ground (in the load). Because I live in Argentina, I need the IEC standard values.
A TT system was well explained by "skogsgurra" and "ScottyUK".
So, if anyone knows the IEC Standard were I can find this, I will be very thanksful.
Thanks again and sorry about my english.
Martin

RE: Tension between neutral and ground

Thanks skogsgurra and ScottyUK.
We used to see "T-T" lighting transformers. It was an adaptation of the old Scott two phse to three phase connection. It was used with two transformers to transform three phase to three phase. Often 480 V to 120/208 V.
I was pretty sure that it didn't fit this question.
Respectfully

RE: Tension between neutral and ground

giordanonaval,

The relavant IEC standard which specifies the TT/ TNS systems is IEC 60364 series. Since IEC are a set of specifications and not installation codes like NEC/ CEC, IEC 60364 doesnot specify a maximum allowable N-E potential.

Based on IEC 60364 series, IEE Wiring Regulations 16 th Edition (BS 7671) is the installation code in IEC/ BS world. Even in that, nothing has mentioned about the max. alloawble potential between N-E.

But as per the TT topology, the maximum possible potential between N-E should be equal to ZERO.

"Because I live in Argentina, I need the IEC standard values"

What is your electrical installation code in Argentina?

Hope this helps!

RE: Tension between neutral and ground

(OP)
Thanks kiribanda
By I understand, the maximum potencial in not equal to zero.

"What is your electrical installation code in Argentina?"

If when you say "code" means "standard", In argentina we use IRAM standard that is extracted from the IEC.
Please teel me if this is ok for you
Sorry about my english
Best regards

RE: Tension between neutral and ground

The voltage between neutral and ground will be the product of the current and the impedance of the current path. If this is a system with a neutral conductor connected from  the source to the service, the total impedance will be only slightly less than the impedance of the neutral conductor from the source to the service (or from the source to the point of the ground fault).
You may use the impedance of the neutral path and the available phase to ground/neutral asymetrical fault current to estimate the maximum neutral to ground voltage. If you feel that it is too high for safety, you may lower it by adding parallel neutral conductors. That is, reducing the neutral impedance.
Note that the voltage from the neutral to the source ground may be much more than the voltage from the neutral to the service ground. In the event of heavy fault currents you may develop "touch and step potentials" in the vicinity of the ground rods. The touch and/or step potentials will not be as severe with ground grids.
Sorry, I can't help you with the code reference as to what the voltage limit is.
respectfully.

RE: Tension between neutral and ground

giordanonaval,

"In Argentina we use IRAM standard that is extracted from the IEC"

So did you check whether there is a specified allowable maximum potential between N-E?

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources