×
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

3 Phases to 2 phases.

3 Phases to 2 phases.

3 Phases to 2 phases.

(OP)
I've assembled a 3 phase motor starter for a 1/2hp pump that was, "going to be 3 phase", but is now "going to be single phase".

It's a small contactor with electronic overloads.  I don't really want to rip these out (it's all 2x) since next week it will probably relapse to, "it's going to be 3 phase", again.

The contactors are more than adequate for the current change.

Does anyone see a problem with just running the second phase back thru the third phase so the electronic overloads remain happy and the system remains three phaseable?

Keith Cress
kcress - http://www.flaminsystems.com

RE: 3 Phases to 2 phases.

That's usually the fix. All it will care about is that current is flowing through all 3 elements, it's not going to be comparing phase angles or anything. What brand of SSOLs?

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
  
For the best use of Eng-Tips, please click here -> FAQ731-376: Eng-Tips.com Forum Policies  

RE: 3 Phases to 2 phases.

I agree with Jeff.

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

RE: 3 Phases to 2 phases.

Thats how its tested (1 phase) in the field.  Loop a single phase current through all three phases.

RE: 3 Phases to 2 phases.

those look like standard thermal rather than electronic.

You'll be lucky if one selected for three phase current will turn up enough to cover the equivalent single phase current

RE: 3 Phases to 2 phases.

I'm not familiar with electronic overloads.

What happens if you left a phase with no current... unbalance trip?  (and the unbalance based on magnitude, not considering phase angle?)

=====================================
(2B)+(2B)'  ?

RE: 3 Phases to 2 phases.

(OP)
Hmmm.. It states protection is:
Differential
Phase loss
and
Overcurrent.

It doesn't really say "electronic" does it..

I don't expect it to cover the entire range with just one model.

Funny thing.. Today they said, "Ah, I think we're going to stick with three phase."

This was after they'd decided 120V single phase on Thursday.


EP that's what the discussion on running one phase back thru the third set was about.

What exactly do they mean about Differential?

Keith Cress
kcress - http://www.flaminsystems.com

RE: 3 Phases to 2 phases.

Differential means it will trip if the current through each pole isn't the same, they are pretty low tech, each pole has a resistance in it which heats up with current flow and mechanical linkages trip it if either all three poles are passing too much current or one pole is different to the others.

As others have mentioned, on single phase motors the trick is to loop a current path back and put it through the overload again so you end up with each pole carrying the same current.
 

RE: 3 Phases to 2 phases.

It is just a fairly basic bimetallic overload so you just pass current through each pole by looping if necessary.

The story would be different if you had used an electronic LS overload. They monitor for phase order and phase loss and they look for more than simply having current in each phase.
 

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