ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
ShoutChat
Recent Posts
Canada for the win
by gfretwell - 12/06/22 08:28 PM
Tiny Homes and the NEC
by gfretwell - 12/06/22 01:43 AM
EMC Glands on Motors
by Trumpy - 12/01/22 06:12 AM
Ground Rods: Installation and Hook-Up
by Trumpy - 12/01/22 05:54 AM
Happy Thanksgiving all!
by gfretwell - 11/30/22 05:55 PM
New in the Gallery:
240/208 to a house
240/208 to a house
by wa2ise, October 9
Now you know.
Now you know.
by Tom_Horne, September 7
Who's Online Now
0 members (), 36 guests, and 10 robots.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate Thread
Joined: Sep 2002
Posts: 1,498
Likes: 1
C
C-H Offline OP
Member
Hi,

I've been scratching my head over something. I have a scenario (theoretical) where you can either use 2 wires @ 230V or 3 wires @ 200V 3-ph. The size of the wires is limited by voltage drop, which is the same percentage wise for both cases. According to textbooks and common knowledge, 3-phase is more efficient than just using two wires. But I fail to arrive at this result in this case.

If I put 1A load the 3-ph case I need 1.73/1.15 = 1.5A single phase to get the same power. This means I have to increase the cross sectional area of the conductors by 50% compared to the 3-phase case. But I only need 2 wires instead of 3 and am back at the same amount of copper.

Is there something wrong with my calculations? Wouldn't be the first time... [Linked Image]

Joined: Apr 2002
Posts: 2,527
B
Moderator
C-H, that is a great riddle/brainteaser. The “trick” is 3ø versus 1ø power must be compared at the same voltage.

1.5 amperes at 230V 1ø is 345VA, where
1 ampere at 200V 3ø is 346.4VA, BUT
1 ampere at 230V 3ø is 398.4VA.
Ratioing, 345/398.4 yields 0.866, exactly as expected.

Does that help?

Joined: Sep 2002
Posts: 1,498
Likes: 1
C
C-H Offline OP
Member
Thanks! I needed to check my calculation with someone. I wanted the same potential to ground for both cases (wye or center tapped source).

By the way, are you and Busbar one and the same person?

Joined: Sep 2003
Posts: 650
W
Member
C-H,

You've found an identity [Linked Image] (In the mathematical sense.) For the same potential to neutral and the same 'aggregate current', you get the same VA delivered to the load, no matter 1 phase or 3 phase or 17 phases [Linked Image]

-Jon

Joined: Apr 2002
Posts: 2,527
B
Moderator
C-H — Yes, but only on alternate Tuesdays. ;-)


Link Copied to Clipboard
Featured:

Tools for Electricians
Tools for Electricians
 

* * * * * * *
2023 National Electrical Code (NEC)
2023 NEC Now Available!
 
* * * * * * *

2020 Master Electrician Exam Preparation Combos
2020 NEC Electrician
Exam Prep Combos:
Master / Journeyman

 

Member Spotlight
electure
electure
Fullerton, CA USA
Posts: 4,289
Joined: December 2000
Top Posters(30 Days)
Trumpy 6
NORCAL 3
Popular Topics(Views)
300,614 Are you busy
230,296 Re: Forum
215,079 Need opinion
Powered by UBB.threads™ PHP Forum Software 7.7.5