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Old 06-02-2012, 01:58 AM   #1
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Single Phase Panel from Three phase 3 Wire Delta


I currently have 200 amp 3 phase 3 wire delta service and limited slots on the main panel. Since I have several pieces of equipment that require single phase 240, I would like to wire in a single phase panel. I just picked up a nice 150 amp EQ tub. My question is regarding the correct wiring. Since there is no neutral available, I am not entirely sure how to wire this correctly. I did notice that the neutral bars in the three phase panel are simply jumped. Also, the EQ panel, since it's 150 amp, has 4 poles on the main. Any advice would be greatly appreciated. In addition, since there is a trough from the main disconnect with connection lugs, I plan to come right out of there (with two wires) and into the single phase panel, instead of using a breaker in the main, 3 phase panel.

Thanks in advance!

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Old 06-02-2012, 06:14 AM   #2
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Single Phase Panel from Three phase 3 Wire Delta


This doesn't sound like a project for a DIYer at all. I suggest you call an electrician and then determine if you can even install a sub panel off the existing panel. It sounds like you will be overloading the service.
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Old 06-02-2012, 06:46 AM   #3
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Single Phase Panel from Three phase 3 Wire Delta


For 240 volt only equipment (not 120/240 volt with neutral) you can add a 3 phase subpanel with double and/or triple breakers of a kind where if one breaker element (pole) trips, the entire twosome or threesome flips off. Nothing at all is connected to the neutral bus bar. Balance the various loads among the three phases, each load connected to two screws of the same double or triple breaker.

YOu may need to a load calculation before starting the project and pulling the permits.

A 240 volt 3 phase system has either an asymmetric neutral or no neutral.

If there is a neutral, then measure hot to neutral for all three phases. Two of the phases should register 120 volts; you can run them to a single phase 120/240 volt subpanel for small loads. Don't use the third phase here which is about 208 volts to neutral.
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Last edited by AllanJ; 06-02-2012 at 07:02 AM.
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Old 06-02-2012, 01:29 PM   #4
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Single Phase Panel from Three phase 3 Wire Delta


Thanks for the responses guys.

K_Buz, I am working with an electrician on this project. What makes you think that the service will be overloaded? Load calculations have been done and all branch circuits have been designed. Everything seems in order and within code.

AllanJ,

The secondary on the supply transformer is three wire delta so no neutral and of course L-L is and P-L is 240V. I understand what you are saying about the breakers but I don't plan on installing a sub panel from the main breaker panel but directly from the trough, which is fed from the main disconnect (fused of course). I have a fused disconnect that I was thinking I might install for added protection but this doesn't seem necessary as the panel will have protection from its main breaker (150 amp).

I guess this project is a little too much for this forum but I have to disagree with K-Buz about not being a DIYer project. With proper safety and always keeping code in mind, as well as getting everything checked from an electrician, anything is possible. I have tackled several commercial projects with great success, this one just seems to be a bit tricky.
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Old 06-02-2012, 02:09 PM   #5
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Single Phase Panel from Three phase 3 Wire Delta


Your sub panel must be rated for a delta feed. Not 240/120.
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Old 06-02-2012, 02:09 PM   #6
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Single Phase Panel from Three phase 3 Wire Delta


Quote:
Originally Posted by bsps View Post
I guess this project is a little too much for this forum but I have to disagree with K-Buz about not being a DIYer project. With proper safety and always keeping code in mind, as well as getting everything checked from an electrician, anything is possible. I have tackled several commercial projects with great success, this one just seems to be a bit tricky.
It's not a complicated project, and many of the people here are more than qualified to advise on it, but it is outside the scope of this forum. In almost every jurisdiction, commercial work must be performed by a licensed electrician.

With that said, you do not need or want a single phase panel for your 240V single phase loads. That would be counterproductive and would result in a large load imbalance between phases. You install 2-pole breakers in a 3-phase panel and distribute the load evenly among the three phases.
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Old 06-02-2012, 02:20 PM   #7
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Single Phase Panel from Three phase 3 Wire Delta


Maybe go to www.electriciantalk.com .They always can help out.
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Old 06-02-2012, 08:36 PM   #8
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Single Phase Panel from Three phase 3 Wire Delta


m, you're totally right and thanks for the info. The reason for trying to throw in a sub panel was a limited amount of slots on the main. Just going to get a new tub with more slots and run single phase branch circuits from there. Will be way easier anyway.

I will give electrician talk a try for any other questions. Thanks guys.

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Old 06-02-2012, 08:43 PM   #9
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Single Phase Panel from Three phase 3 Wire Delta


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K_Buz, I am working with an electrician on this project.
Then why isn't he doing this work?
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Old 06-02-2012, 08:44 PM   #10
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Single Phase Panel from Three phase 3 Wire Delta


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Maybe go to www.electriciantalk.com .They always can help out.
Just as a point of reference, ET.com is a "professional only" site. This is very common of this type of site.
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