can someone check my 3 ph question?

Reply

  #1  
Old 01-02-19, 11:16 AM
Member
Thread Starter
Join Date: Oct 2005
Location: USA
Posts: 1,358
Received 10 Votes on 10 Posts
can someone check my 3 ph question?

Its a boat/marina question. Sometimes the pedestal is supplied by split 240V/120, but sometimes its 2 legs of 208V. If it is the 208/120V Y arrangement, and I have a 10A load on EACH of the two supplied 120V leg, then what is my neutral current? My vector graph on a napkin shows me 10A/1.7 or about 5.8 Amps.

ie; its not full 3 ph, only 2 legs.
 
Sponsored Links
  #2  
Old 01-02-19, 11:30 AM
Tolyn Ironhand's Avatar
Group Moderator
Join Date: Nov 2007
Location: Twin Cities, MN
Posts: 12,965
Received 59 Votes on 52 Posts
(I didn't do the math) here is the formula to calculate it out: https://www.hunker.com/12470226/how-...utral-currents
 

Last edited by Tolyn Ironhand; 01-02-19 at 05:38 PM.
  #3  
Old 01-02-19, 12:00 PM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,944
Received 42 Votes on 40 Posts
You don't do the division by 1.7. When your phase currents are 10A, 10A and 0A, the neutral current will be 10A , assuming resistive or mostly resistive loads. Motors will cause enough shift to have measurably different than 10A.
 
  #4  
Old 01-02-19, 12:01 PM
Member
Thread Starter
Join Date: Oct 2005
Location: USA
Posts: 1,358
Received 10 Votes on 10 Posts
10A it is, per posts 2 and 3; glad I asked!
 
  #5  
Old 01-02-19, 12:11 PM
Member
Thread Starter
Join Date: Oct 2005
Location: USA
Posts: 1,358
Received 10 Votes on 10 Posts
Quite non-intuitive.

If you hold A phase current at 10Amps, C always zero, and vary B phase current, here are some results.

A=B=10; Neut = 10A
A=10, B=0: Neut = 10A
A=10, B-5; Neut = 8.7A

interesting indeed.
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes
 
Ask a Question
Question Title:
Description:
Your question will be posted in: