ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
Shout Box
Recent Posts
Changing a Bulb
by mbhydro. 07/21/18 05:57 PM
Opinions & comments
by HotLine1. 07/21/18 04:44 PM
Tray cable?
by gfretwell. 07/11/18 10:18 PM
Eaton Heavy Duty 30A and 60A Safety Switches
by Admin. 07/11/18 09:49 PM
ORTOVOX Recalls Avalanche Transceivers
by Admin. 07/11/18 09:44 PM
New in the Gallery:
Plug terminals
Housebilding DIY wiring
Who's Online Now
0 registered members (), 25 guests, and 22 spiders.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate Thread
Load Calculations #130384
03/20/06 06:34 PM
03/20/06 06:34 PM
R
rhpope  Offline OP
Member
Joined: Feb 2006
Posts: 18
North Carolina
When calculating the load for a building, how do you spread the single and three phase loads over the incoming three phase lines? I belive the correct way for 120/208 Wye is that single phase 208 or 240 loads spread equally across two transformers (A&B, B&C, or C&A) whereas for 120/240 Delta, 208 or 240 single phase load is applied to only one transformer (A, B, or C)/phase (just as the 120 loads are only on the A & C phases). The three phase loads are spread equally across all three phases.

Tools for Electricians:
Re: Load Calculations #130385
03/20/06 09:18 PM
03/20/06 09:18 PM
L
Larry Fine  Offline
Member
Joined: Feb 2005
Posts: 693
Richmond, VA
You seem to have it correct. The only thing that's really tricky is that, on a delta with a high leg (B phase), any load that has a neutral connection, i.e., 240/120 or just 120, must be connected only to the other two phases (A or C), as you noted.

Typically, the high-leg delta system has less load on B phase than the other two, because only line-to-line or 3-phase loads are served by this phase, whereas A nd C phases serve all of the line-to-neutral loads.


Larry Fine
Fine Electric Co.
fineelectricco.com
Re: Load Calculations #130386
03/20/06 10:39 PM
03/20/06 10:39 PM
D
Dnkldorf  Offline
Member
Joined: Dec 2004
Posts: 1,064
nowhere usa
I agree with your thinking about spreading the loads as equally as you can, which would be balancing of the transformer.

Using a 208/120Y transformer you can use any of the phases for 120V loads, any 2 of the phases for single phase 208V loads and all three for 3 phase 208V loads. However you can't use any combination of these for 240V loads...

Using a 240/120 Ct transformer, you can use A or C phase for 120V loads, any 2 phases for single phase 240V loads, and all 3 for 3 phase 240V loads. You can't use any combination for 208V loads....

Mind you with this type setup and using the high leg, you must be concerned about using full voltage breakers where with the 208/120Y setup, the use of "slash" breakers could be used.


Dnk...



[This message has been edited by Dnkldorf (edited 03-20-2006).]


Featured:

2017 Master Electrician Exam Preparation Combos
2017 NEC Electrician
Exam Prep Combos:
Master / Journeyman

 

Member Spotlight
JoeKP
JoeKP
Berkley, MA
Posts: 144
Joined: March 2008
Show All Member Profiles 
Top Posters(30 Days)
Admin 5
Popular Topics(Views)
248,168 Are you busy
185,639 Re: Forum
175,010 Need opinion
Powered by UBB.threads™ PHP Forum Software 7.6.1
(Release build 20180101)
Page Time: 0.022s Queries: 15 (0.004s) Memory: 0.9515 MB (Peak: 1.0785 MB) Zlib enabled. Server Time: 2018-07-23 06:02:53 UTC