×
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

Neutral and earth for a 3 phase motor

Neutral and earth for a 3 phase motor

Neutral and earth for a 3 phase motor

(OP)
Hello,

I have a contractor who wants to use a signle conductor for both earth and neutral, but from what i read here in your posts "neutral shall be connected to earth only at the service entrance" - so is there a breach of the code in him doing so?

Another thing - i don't think the Search service works because for the nth time i try and i get no results, could you please give me an example of a search that gives results? :)

RE: Neutral and earth for a 3 phase motor

Why would he use Neutral for a three-phase motor?

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: Neutral and earth for a 3 phase motor

What is permissible by code depends on where you are and what code applies.  Per the NEC rules, neutral and ground are always separate for low voltage (not over 600V in the NEC) systems; some exceptions for higher voltages.  On the other hand there is no reason to take a neutral to a 3-phase motor.

Putting the words neutral earth into the search box at the top of the page produced no results.  Putting those words in the Google Search for Eng-Tips Forums provided over 200 results, clicking on advanced search and using those key words for the forums in my thread minder list resulted in "hundreds of results matched your query".

RE: Neutral and earth for a 3 phase motor

(OP)
Ok - no matter what i want to apply NEC.

Why wouldn't i need a neutral, do all 3 phase motors have a detlta connection? The motors are direct on line, but for star-delta, i will give him only 1 cable to the starter, from there to the motor he has to run 2, is the cable for star delta also 3 cores without neutral?

or is the reason that the neutral current is perfectly zero, therefore no need for the wire?

RE: Neutral and earth for a 3 phase motor

Even in wye connected motors the wye point is not brought out for connection.  Three terminations, three conductors; plus a safety ground.  No place for a neutral.

See thread237-169272.

RE: Neutral and earth for a 3 phase motor

Also, for Start-Delta starting capability you must run 6 leads to the motor because the Star and Delta connections are then made in the contactors, not the motor. But you would still  only need one ground conductor.

JRaef.com
"Engineers like to solve problems.  If there are no problems handily available, they will create their own problems."   Scott Adams  
For the best use of Eng-Tips, please click here -> FAQ731-376

RE: Neutral and earth for a 3 phase motor

(OP)
Ok, thank you very much for the info. In conclusion: 3 phase motors have no terminal for neutral, only for earth, therefore a neutral conductor will have no termination and hence it is not necessary. Thanks again.

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