3 phase box question

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  #1  
Old 03-03-16, 12:29 AM
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3 phase box question

Hello everyone,

I have a 3 phase box with one leg having a higher voltage than the others when going through the neutral. My question is on setting up a 240 volt connection. If I set up a 240 volt connection can I go through any 2 leg combinations. So if I give the legs the names A, B, and C. I can do all possible combinations of 2: AB, AC, or BC.

Thank you
 
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  #2  
Old 03-03-16, 01:35 AM
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Normally, with a true three phase service you'd see 120v from each phase to neutral and 208v between each phase.

With you having 240v between phases and one leg higher..... it sounds like you have a two transformer derived three phase service. Your third leg is a high leg also called a b*astard or red leg. You'd never want to connect a 120v load to that phase.

If all your loads are 240v..... it's best to balance them equally among the phases like you described...... AB, AC, or BC.
 
  #3  
Old 03-03-16, 08:50 AM
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It's also worth noting that the high leg should always be marked with orange tape or pulled with orange wire to be NEC compliant. Part of the way to know it should never be connected to 120V loads as PJ stated.
 
  #4  
Old 03-03-16, 06:06 PM
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Make sure the breakers attached to the high leg are rated straight 240 as the slash rated 120/240 are only good for 120 to ground legs.
 
  #5  
Old 03-03-16, 06:17 PM
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I really do appreciate the replies. I am having trouble locating exactly what you are referring to Astuff. This is all I can find: Siemens Q260 60-Amp 2 Pole 240-Volt Circuit Breaker - - Amazon.com Does that work? And If I only use it for 240 volt does it matter that I have one that states 120/240?

Thanks as always
 
  #6  
Old 03-03-16, 07:59 PM
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The Siemens Q260 breaker is really rated at 120/240 volts. For a 240 volt rated breaker you need a Q260R circuit breaker.

http://w3.usa.siemens.com/powerdistr...01-034-037.pdf
 
  #7  
Old 03-03-16, 09:55 PM
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Thanks,

It looks like what I have is a cutler hammer box. OOOps.... Where can I find the appropriate circuit breaker for that?

Thanks a lot.
 
  #8  
Old 03-03-16, 10:01 PM
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What is the style...... BR, CH, etc. ?

Check the panel cover or on a breaker.
 
  #9  
Old 03-03-16, 10:28 PM
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It matters that you use the correct breaker. Here is one explanation with a graphic: Requirements for Slash Versus Straight Voltage Rated Breakers and More
 
  #10  
Old 03-03-16, 11:24 PM
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It says CH on it. But I searched the internet for a breaker that is already in the box. Sense this double pole breaker is 120/240 it doesn't go through the High leg but I would like to use the High leg for power usage reasons.



No matter how much I look I cannot find a 60 amp CH 240 volt double pole breaker
 
  #11  
Old 03-04-16, 07:02 AM
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The CH series does not appear to have straight 240 in a two pole. I see only the three pole CH3xx is 240 rated.
https://www.platt.com/CutSheets/Eato...rs-CH-Type.pdf
 
  #12  
Old 03-04-16, 12:02 PM
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Can I use some generic or other brand for this? I find it remarkable that I cannot get what is needed for this..
 
  #13  
Old 03-04-16, 01:57 PM
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Yes you can use the 240V tri-pole CH breaker and just not connect a wire to one of the poles. You cannot use another brand breaker in that panel.
 
  #14  
Old 03-05-16, 01:02 PM
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Hmmm... I think using this tri-pole 240V would then open up more options for me. Excellent. From what I understand from these Tri-poles I can get 3 separate circuits at 240V from one tri-pole breaker. Well, If I use one tripole breaker at 60amps with legs I will name A, B, and C, can I then get three separate 60 amp 240V circuits if I have these combinations with 6 gauge wire attached: AB, AC, and BC. I think I might need another 60 amp 240V circuit in the future. I don't think I will need a third one, but you never know.

Thanks
 
  #15  
Old 03-06-16, 08:11 AM
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I can get 3 separate circuits at 240V from one tri-pole breaker.
I'm not following you. A three pole breaker would have up to three wires connected (one to each leg) so you would not normally have multiple circuits.

A MWBC doesn't really work here either as for a high leg delta two of the wires would be 120v with one at 208.
 
  #16  
Old 03-06-16, 02:09 PM
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Hello,

I appreciate the reply as always. I have made a drawing so that you can understand what I mean. Hopefully this helps. I did my best.
Name:  ab.jpg
Views: 152
Size:  35.1 KB
 
  #17  
Old 03-06-16, 03:36 PM
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That is not how it works. A three pole breaker will only give you a single 60 amp circuit, whether you use two legs for a single phase load, or all three for a three phase load.
 
  #18  
Old 03-06-16, 04:08 PM
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Ok. I am running out of room in my breaker box so will have to think of something else. Three phase is really confusing.


I appreciate that help as always.
 
  #19  
Old 03-06-16, 04:14 PM
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You can always add a sub panel next to this panel. Since you have a high leg 3 phase panel you could just install a single phase panel fed by a two pole breaker. The two pole breaker would need to be installed so it is NOT on the high leg. That single phase panel would be more or less the same as a panel you would find in a house.
 
  #20  
Old 03-06-16, 04:43 PM
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OR.......install a 100 amp 3P Type CH breaker and an adjacent panelboard that accepts bolt-in breakers. It is much easier to find 240 volt rated breakers of the bolt-in variety.
 
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