3 phase feeding single phase panels

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In this case, its a mixed use type of place where there could be some shops, artist's studios, live work etc. I dont yet have a formal figure on how many are in fact legally dwelling units. So three phase could be beneficial of course. I am guessing the meter stacks would see a significant cost increase from single phase to 3. Single phase of course has the advantage of 2 CCC per feeder if several were to be installed in one raceway.
 
electrofelon said:
In this case, its a mixed use type of place where there could be some shops, artist's studios, live work etc. I dont yet have a formal figure on how many are in fact legally dwelling units. So three phase could be beneficial of course. I am guessing the meter stacks would see a significant cost increase from single phase to 3. Single phase of course has the advantage of 2 CCC per feeder if several were to be installed in one raceway.
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If it is supplied from a wye system (like 208/120 volts) then the neutral is only a non current carrying conductor for ampacity adjustment purposes when it carries unbalanced current from all three phases.
 
electrofelon said:
Oh right. Got mixed up comparing 120/240 single phase to 120/208 three phase. 120/240 won't be in this building at all
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Here is when neutral IS NOT counted as a CCC:
Regardless of the imbalance of currents, because the total heat in all wires when unbalanced will not exceed the maximum it can be in just the line wires when balanced. This assumes the loads are linear or close to it.
Nonlinear loads with lots of harmonics may require counting it. How to quantify that, I have no idea.
808ecmCBfig4.jpg



Here is when neutral IS COUNTED as a CCC. No matter how balanced the L2 and L3 current may be. The neutral is an integral part of the round trip path.
110ecmCQfig1.gif
 
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What I have not noticed anyone mention is that regardless of costs the fact remains that at some point the power company is going to tell you you are getting a three phase service. They typically are not going to provide a 1,000 amp single phase service etc.
 
iwire said:
What I have not noticed anyone mention is that regardless of costs the fact remains that at some point the power company is going to tell you you are getting a three phase service. They typically are not going to provide a 1,000 amp single phase service etc.
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It is rare that they would do anything that large on single phase, although in some cases they have no other choice than to provide large 1-phase services, or spend a fortune to upgrade the utility feeders.

I've done a project with a 600A single phase service, and a project with a 1200A single phase service. There was no 3-phase power available for miles, and the POCO agreed that this was the most reasonable solution.
 
iwire said:
What I have not noticed anyone mention is that regardless of costs the fact remains that at some point the power company is going to tell you you are getting a three phase service. They typically are not going to provide a 1,000 amp single phase service etc.
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In the city that is probably true most of the time, out in middle of nowhere (which I work at a lot) not always the case. Sometimes in those instances we really wish we could have three phase but owner is not willing to pay what POCO wants for costs to get three phase to them, other times we may be lucky for them to at least get open delta system supplied by two primary phase conductors and the primary neutral.
 
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