120/208 3phase and 120/240 single with 3 cans - Electrician Talk - Professional Electrical Contractors Forum
CLICK HERE AND JOIN OUR COMMUNITY TODAY, IT'S FREE!
Go Back   Electrician Talk - Professional Electrical Contractors Forum > Electrical Forum > General Electrical Discussion


Reply
 
Thread Tools Display Modes
Old 06-26-2015, 07:52 PM   #1
Senior Member
 
Join Date: Apr 2014
Location: Northern Maine
Posts: 158
Rewards Points: 265
Default 120/208 3phase and 120/240 single with 3 cans

I was talking with a lineman (which I am NOT!) about a service they had to do. One pole and there was a need for 120/208 for a building and next door was a resi service. He said he thought you could do it with only three cans, which I think to be true. But the POCO made them install 4 cans with the resi being dedicated just to that service.

Couldn't this be done in a typical 208Y if one of the unused taps were brought over for the 120/240 service as all the center taps would be bonded anyway?

A typical 120/208 service uses three tap cans (120-0-120) on the pole with only one tap and the center tap used leaving half the secondary unused on all three cans....each one only produces 120V, but would still have 240 available if the other tap was used?

I could see some possible balancing issues with maybe a larger can and two smaller is the 120/240 load were significant. Just having some good electrical discussion.

TWN
TheWireNut is offline   Reply With Quote
Join Contractor Talk

Join the #1 Electrician Forum Today - It's Totally Free!

ElectricianTalk.com - Are you a Professional Electrical Contractor? If so we invite you to join our community and see what it has to offer. Our site is specifically designed for you and it's the leading place for electricians to meet online. No homeowners asking DIY questions. Just fellow tradesmen who enjoy talking about their business, their trade, and anything else that comes up. No matter what your specialty is you'll find that ElectricianTalk.com is a great community to join. Best of all it's totally free!

Join ElectricianTalk.com - Click Here JOIN FOR FREE


Warning: The topics covered on this site include activities in which there exists the potential for serious injury or death. ElectricianTalk.com DOES NOT guarantee the accuracy or completeness of any information contained on this site. Always use proper safety precaution and reference reliable outside sources before attempting any construction or remodeling task!

Sponsored Links
Advertisement
 
Old 06-26-2015, 08:08 PM   #2
Senior Member
 
Join Date: May 2015
Location: Sacramento, California
Posts: 13,957
Rewards Points: 26,160
Default

A 208Y120 single phase Service uses a different meter socket than a 240/120 two leg Service.

Right there, that's a show stopper for the Poco.

All Poco's have found out that being too clever -- bites them back.
telsa is online now   Reply With Quote
Old 06-26-2015, 08:35 PM   #3
Senior Member
 
Join Date: Apr 2014
Location: Northern Maine
Posts: 158
Rewards Points: 265
Default

Quote:
Originally Posted by telsa View Post
A 208Y120 single phase Service uses a different meter socket than a 240/120 two leg Service.

Right there, that's a show stopper for the Poco.

All Poco's have found out that being too clever -- bites them back.
We are talking about two separate services on two separate buildings. one with 120/208 three phase and one 120/240 single phase. Two meters.

TWN
TheWireNut is offline   Reply With Quote
Sponsored Links
Advertisement
 
Old 06-26-2015, 09:17 PM   #4
Bilge Rat
 
Join Date: Aug 2007
Location: Fernley, Nevada (near Reno)
Posts: 6,580
Rewards Points: 2,770
Default

With typical pole-mount pots, there are 2 - 120 volt windings on the secondary. When the service is 120/240, they are connected in series with the common connection being the center bushing.

When the service is 120/208, they are connected in parallel and only 2 bushings are used, usually the two outside ones. The 3rd bushing (usually the center one) is not connected.

But I see what you're saying. If one of the pots were connected in series (120/240 and all 3 bushings used) then yes, that one would supply both single phase and one phase of the Y.

The problem is that pot could easily be grossly overloaded if both the single and 3 services were in use at the same time. Going to a larger pot would pose problems as well; the impedance would be different resulting in voltage imbalance in the 3 service, plus 1/3 of the pots capacity could never be utilized.

Plus, very few linemen would have even the slighest clue how to troubleshoot it if a problem ever arose..........lol. Let alone actually hook it up.
micromind is offline   Reply With Quote
The Following 4 Users Say Thank You to micromind For This Useful Post:
JW Splicer (06-26-2015), Rollie73 (06-26-2015), tates1882 (06-26-2015), TheWireNut (06-27-2015)
Old 06-27-2015, 10:00 AM   #5
Senior Member
 
Barjack's Avatar
 
Join Date: Mar 2010
Location: St. Petersburg, FL
Posts: 898
Rewards Points: 280
Default

I'm really confused here.

Here is what I think I know:

In a wye system, one end of each secondary winding is connected to the one end of the other two, producing a common point, the neutral.

The "floating" ends of the wye are 208V L-L, and 120V L-N.

So, where would the 240V come from?
Are you saying there is an extra winding in each secondary, that is not being used in a wye configuration, and if connected in series with one of the legs it would produce 240V?

So, would one of the line phases in the wye system actually be the neutral in the 120/240 system, which would actually be 240V L-N on the wye with the extra winding?

Apologies if this makes no sense.
Barjack is offline   Reply With Quote
Old 06-27-2015, 11:13 AM   #6
Bilge Rat
 
Join Date: Aug 2007
Location: Fernley, Nevada (near Reno)
Posts: 6,580
Rewards Points: 2,770
Default

In a typical pole-mount pot, there are two 120 volt windings. for a 120/240 service, they are connected in series. The point of connection becomes a center tap and it is connected to the center bushing.

For a 120/208 service, the windings are connected in parallel. Since there are only 2 wires, only 2 bushings are used.

If one of the pots on a 120/208 service is connected in series, both 120 (for the Y service) and 120/240 (for the single phase service) exist. The other 2 pots are connected 120 for the other 2 legs of the Y.
micromind is offline   Reply With Quote
Old 06-27-2015, 12:08 PM   #7
Senior Member
 
Barjack's Avatar
 
Join Date: Mar 2010
Location: St. Petersburg, FL
Posts: 898
Rewards Points: 280
Default

120/208 3phase and 120/240 single with 3 cans-imageuploadedbyelectriciantalk.com1435421317.830396.jpg

If you can read my chicken scratch, would this be the correct wiring diagram?

Wouldn't this create a bonding problem as both neutral points would end up connected together?


Sent from my iPhone using electriciantalk.com
Attached Thumbnails
120/208 3phase and 120/240 single with 3 cans-imageuploadedbyelectriciantalk.com1435421082.668279.jpg  

Barjack is offline   Reply With Quote
The Following User Says Thank You to Barjack For This Useful Post:
TheWireNut (06-27-2015)
Old 06-27-2015, 12:32 PM   #8
professional redneck
 
Join Date: Apr 2011
Location: Quebec, Canada
Posts: 119
Rewards Points: 187
Default

almost this, the center top of the single phase would be the same as the neutral of the 3 phase
metalpats is offline   Reply With Quote
The Following User Says Thank You to metalpats For This Useful Post:
Barjack (06-27-2015)
Old 06-27-2015, 12:46 PM   #9
Senior Member
 
Barjack's Avatar
 
Join Date: Mar 2010
Location: St. Petersburg, FL
Posts: 898
Rewards Points: 280
Default

120/208 3phase and 120/240 single with 3 cans-imageuploadedbyelectriciantalk.com1435423548.771141.jpg

So, this then?


Sent from my iPhone using electriciantalk.com
Barjack is offline   Reply With Quote
Old 06-27-2015, 01:06 PM   #10
Bilge Rat
 
Join Date: Aug 2007
Location: Fernley, Nevada (near Reno)
Posts: 6,580
Rewards Points: 2,770
Default

Quote:
Originally Posted by Barjack View Post
Attachment 58122

So, this then?


Sent from my iPhone using electriciantalk.com
That's it!!!

This connection would work, but the 240 pot will either be overloaded or not used to its capacity.
micromind is offline   Reply With Quote
The Following 2 Users Say Thank You to micromind For This Useful Post:
Barjack (06-27-2015), TheWireNut (06-27-2015)
Old 06-27-2015, 01:12 PM   #11
Senior Member
 
Barjack's Avatar
 
Join Date: Mar 2010
Location: St. Petersburg, FL
Posts: 898
Rewards Points: 280
Default

Quote:
Originally Posted by micromind View Post
That's it!!!



This connection would work, but the 240 pot will either be overloaded or not used to its capacity.

I had no idea those pole transformers had double windings in them.

Thanks for the help!


Sent from my iPhone using electriciantalk.com
Barjack is offline   Reply With Quote
The Following User Says Thank You to Barjack For This Useful Post:
micromind (06-27-2015)
Old 06-27-2015, 08:21 PM   #12
Very Long Vacation
 
Join Date: Jan 2011
Location: united states of america
Posts: 11,766
Rewards Points: 5,262
Default

This thread:

http://www.electriciantalk.com/f2/24...25/#post912964
meadow is offline   Reply With Quote
The Following 2 Users Say Thank You to meadow For This Useful Post:
Barjack (06-27-2015), micromind (06-27-2015)
Old 06-27-2015, 08:23 PM   #13
Very Long Vacation
 
Join Date: Jan 2011
Location: united states of america
Posts: 11,766
Rewards Points: 5,262
Default

Quote:
Originally Posted by Barjack View Post
I had no idea those pole transformers had double windings in them.

Thanks for the help!


Sent from my iPhone using electriciantalk.com

Yup! They parallel them to het 120 volts in a 3 phase bank, series for 120/240. That way both are covered. See above post for diagram.
meadow is offline   Reply With Quote
The Following 2 Users Say Thank You to meadow For This Useful Post:
Barjack (06-27-2015), micromind (06-27-2015)
Old 06-27-2015, 10:12 PM   #14
Senior Member
 
Join Date: Apr 2014
Location: Northern Maine
Posts: 158
Rewards Points: 265
Default

This is exactly why I asked on here! Thanks guys. I was always under the impression that they only used half of the secondary, but they actually parallel them for full capacity. The POCO around here used the center tap for the common or neutral and the other tap is unused. If I could figure out how to post pics on here I certainly would!

TWN
TheWireNut is offline   Reply With Quote
The Following 2 Users Say Thank You to TheWireNut For This Useful Post:
meadow (06-27-2015), micromind (06-27-2015)
Old 06-27-2015, 11:25 PM   #15
Bilge Rat
 
Join Date: Aug 2007
Location: Fernley, Nevada (near Reno)
Posts: 6,580
Rewards Points: 2,770
Default

When paralleled, any 2 bushings will work. Around here, they use the outside 2 and the center one is not connected.
micromind is offline   Reply With Quote
Old 06-27-2015, 11:48 PM   #16
Very Long Vacation
 
Join Date: Jan 2011
Location: united states of america
Posts: 11,766
Rewards Points: 5,262
Default

Quote:
Originally Posted by micromind View Post
When paralleled, any 2 bushings will work. Around here, they use the outside 2 and the center one is not connected.
Double bushing can? They normally pic the center around here because single bushing cans are required to have a ground (can) strap to the neutral bushing.
meadow is offline   Reply With Quote
Old 06-28-2015, 01:05 AM   #17
Bilge Rat
 
Join Date: Aug 2007
Location: Fernley, Nevada (near Reno)
Posts: 6,580
Rewards Points: 2,770
Default

That's interesting; around here, all 3 bushings are isolated and whatever one is to be grounded is done so by connecting the neutral to both the pole ground and the primary neutral/ground.
micromind is offline   Reply With Quote
Reply

Thread Tools
Display Modes

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


Similar Threads
Thread Thread Starter Forum Replies Last Post
120/208 1-ph load in 120/240 environment mikewillnot Commercial Electrical Forum 21 06-08-2015 06:15 AM
240, 4 wire to 120/208 jgs8919 Services and Service Equipment 14 02-04-2014 12:34 PM
120/208/240/480? dietdrkelp General Electrical Discussion 18 10-01-2013 10:36 AM
480/277, 240/120, 208/120 in same bldg THARMON NEC Code Forum 10 03-22-2010 09:28 PM
120/240 high leg to 120/208? deadshort52 General Electrical Discussion 3 01-08-2009 08:52 PM


All times are GMT -4. The time now is 07:19 AM.


Powered by vBulletin® Version 3.8.8
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.1
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
User Alert System provided by Advanced User Tagging (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Our Pro Sites Network
ContractorTalk.com | DrywallTalk.com | HVACSite.com | PaintTalk.com | PlumbingZone.com | RoofingTalk.com