ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
ShoutChat
Recent Posts
Increasing demand factors in residential
by tortuga - 03/28/24 05:57 PM
Portable generator question
by Steve Miller - 03/19/24 08:50 PM
Do we need grounding?
by NORCAL - 03/19/24 05:11 PM
240V only in a home and NEC?
by dsk - 03/19/24 06:33 AM
Cordless Tools: The Obvious Question
by renosteinke - 03/14/24 08:05 PM
New in the Gallery:
This is a new one
This is a new one
by timmp, September 24
Few pics I found
Few pics I found
by timmp, August 15
Who's Online Now
0 members (), 260 guests, and 19 robots.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate Thread
#128499 04/22/03 02:19 AM
Joined: Aug 2002
Posts: 141
E
elecbob Offline OP
Member
Can anyone point me the way to the formula for calculating the neutral current in a 3 phase wye circuit?thanks
bob

Stay up to Code with the Latest NEC:


>> 2023 NEC & Related Reference & Exam Prep
2023 NEC & Related Reference & Study Guides

Pass Your Exam the FIRST TIME with the Latest NEC & Exam Prep

>> 2020 NEC & Related Reference & Study Guides
 

#128500 04/22/03 07:04 AM
Joined: Apr 2003
Posts: 139
B
Member
I do not know of any online versions of the calculation, but I will be happy to post it right here for you.

In = the square root of I^A+I^B+I^C-(IA*IB)-(IB*IC)-(IC*IA)

However, I have found that for field calculations, by determining the load of the greatest unbalance of any two phase loads will give you a very accurate value. EX: A=30amp, B=40amp, C=50amp. The greatest difference is 50-30= 20amp. If you perform the above calculation, the value comes to around 17.32amp. Not close enough for an exam question, but plenty clos enough for field calcs.


Bryan P. Holland, ECO.
Secretary - IAEI Florida Chapter
#128501 05/25/03 09:19 AM
Joined: May 2003
Posts: 26
I
Member
gravity, why does that work? I know it does because I used my HP-11C calculator and assumed that the phases were 120 degrees apart and got the same answer. The way I do it is to convert the polar quantities into rectangular and total them, then convert back to polar. Using the HP it only takes a few seconds once you learn how to do it, faster than your method. If the currents are not 120 degrees apart, then there is a lot of difference in doing it my way and your way. For an electrician, probably doesn't matter. I was a substation test engineer commissioning protective relays and had to know very accurately what the residual currents were. But I am intriqued by your method. Thought at first it was symmetrical components, but ruled that out.

Ichabod


Link Copied to Clipboard
Powered by UBB.threads™ PHP Forum Software 7.7.5