If you had your choice????

If you had your choice????

  • A

    Votes: 6 60.0%

  • B

    Votes: 2 20.0%

  • C

    Votes: 2 20.0%
  • Total voters
    10
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e57

e57

Senior Member
Location
San Francisco, CA
I want a single phase 240/120 RESIDENTIAL service at 600a - I have several options available via the POCO:

A. 240/120 3 phase 400A service - In DELTA - That is if I can get > than the = of 5PH on the high leg, AND get some relative balance on the phases..... No easy task since only a few appliances will take the high leg... And all my single phase loads are over 400 - which is why I need 600 in the first place. Benifit here is COST ($30k) and less hassle from city and POCO, see below. But if I put in two 240/208 transformers at 75kva - I could get a real good balance.... With a mix of delta appliances since many are not rated for 208, and wye general loads and lighting. FUN! Smaller service equipment, and company gets the money for the T's - not poco...

B. Pad mount 208/120 3 phase ~$45k for the work for the trans, but due to location - about another $50 in engineering and rebuilding a massive retaining wall - and no one wants to see it....

C. Underground 208/120 3-phase transformer out in the street - big BIG hassle with the city, and $100k +++
 
I was on board until you mentioned using two 120/208 75kva..................lost me on that!

Are you using some heavy equipment other than possibily a chiiler for your AC? Is this a house?
 
Is a 600 amp single phase 120/240 volt service available or are you stuck with one of the three options?
 
infinity said:
Is a 600 amp single phase 120/240 volt service available or are you stuck with one of the three options?
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Stuck with one of those 3.... Although over-night I thought of a fourth (A - option 2)... This is a residence and most of the loads are 120 and a handfull of 240/120 appliances. Figured I could get a better balance out of wye and put all the 120 stuff on them, like say all of the 200a's of lighting. But on second thought maybe use their split phase, and add two single phase 240P to 240/120 transformers on A-B, and B-C, result being 3 single phase split systems from the delta. Anyone for option A-2?
 
Get the delta service and install your own transformer. Your electrical room is going to be huge anyhow, so a transformer in there shouldn't be a big deal. The cost difference to the next best option is 15 or 20K, and you can plant a transformer for much less than that.
 
I went with "C".

If all 3 choices are legitimate options the company I work for stands to make the most profit from the most expensive option.
 
iwire said:
I went with "C".

If all 3 choices are legitimate options the company I work for stands to make the most profit from the most expensive option.
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When "big" hassle with the city is involved, I shy away. Things normally always go the contractor's way in the end, but I tire of jumping through hoops. Everything's a tradeoff, I suppose.
 
iwire said:
There is a lot of truth in that.
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That is if they even allow it.... And it will entail additional costs - none of which the company I work for will profit from - all POCO fees taken on by the owner directly. (no mark up there.)

Option B is also a non-starter as it will involve a hill side cut on what is now an historical district and must also get city approval as well as encrochment permits.

A-1 or 2 is sounding best now, but adds the element of noise/heat in the building - or noise, camoflage and corrosion if outside. Did some prelim calcs for A-2 and I could get a very good balance that way. A 4-wire delta service feeding two single phase 240/120 transformers, with demand applied is looking at just under 400A.
 
I'm thinking A, but I have to pick it apart first:

e57 said:
A. 240/120 3 phase 400A service - In DELTA - That is if I can get > than the = of 5PH on the high leg, AND get some relative balance on the phases..... No easy task since only a few appliances will take the high leg... And all my single phase loads are over 400 - which is why I need 600 in the first place.
Click to expand...
Any line-to-line loads that do not use the neutral, such as HVAC, water-heaters, etc., can be connected between either 120v line and the high leg.

But if I put in two 240/208 transformers at 75kva - I could get a real good balance.... With a mix of delta appliances since many are not rated for 208, and wye general loads and lighting.
Click to expand...
Why transformers? A Delta supply delivers 240v line-to-line, not 208v. Plus, 240-to-208v transformers might overload the usually-smaller high leg conductor.

Use single-phase panels for receptacles, lighting, and other neutral-using 120v and 120/240v equipment, and 3-phase panels for 240v-only loads.
 
LarryFine said:
I'm thinking A, but I have to pick it apart first:
Click to expand...
Me too.... But please do - I'm looking for ideas here.

Any line-to-line loads that do not use the neutral, such as HVAC, water-heaters, etc., can be connected between either 120v line and the high leg.
Click to expand...
Not enough of them to make the 'spread' for getting the split phase below 400A, 80% of the load is 120 L-N loads

Why transformers? A Delta supply delivers 240v line-to-line, not 208v. Plus, 240-to-208v transformers might overload the usually-smaller high leg conductor.
Click to expand...
They can give me full-size on the high leg in the neighborhood - I was intitially thinking customer owned wye transformers from the delta service to help balance them, but have found it kind of a math quandry to get both below 400a, and balance this way unless I use either larger transformers, or one large enough for the whole kit and kabootle. Which is why I am now thinking two single phase 240 primarary - 240/120 secondaries. Since most of the 240 stuff is 3-wire, and not dual rated for 208. Then I end up with 3 split phased systems, and I can actually use them. (One from the service, and two from the T's)

Use single-phase panels for receptacles, lighting, and other neutral-using 120v and 120/240v equipment, and 3-phase panels for 240v-only loads.
Click to expand...
Forgot to mention most of the feeders have been run at this point for single phase 240/120.

150000/(240*1.732) = 360A in a perfect world....:rolleyes:
 
LarryFine said:
I'm thinking A, but I have to pick it apart first:

Any line-to-line loads that do not use the neutral, such as HVAC, water-heaters, etc., can be connected between either 120v line and the high leg.
Click to expand...


How much is 240 volt rated 2 pole breakers going to cost & how hard are they to get? Since standard 120/240V rated breakers can't be used on the high leg....
 
norcal said:
How much is 240 volt rated 2 pole breakers going to cost & how hard are they to get? Since standard 120/240V rated breakers can't be used on the high leg....
Click to expand...
Actually, many 2- and 3-pole breakers are straight 240v rated.
 
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