Help with sizing parallel service conductors

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mike1061

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I'm in Chicago, with the 2017 NEC with modifications. A commercial catering business, no other tenants in the building. I did the load calculation some time ago and came up with 800 amps, 120/240 volt 3 phase. The owner has asked me to bid both 800 amps and 1000. So I've come up with these 3 options. Please look over and see what I have wrong.
option 1) 800 amps
Table 310.15(B)(16) 75*C column
2-sets of 600 kcmil, 420 amps ech, = 840 amps.
Table C.1
2 sets of 4) 600 kcmil 3 1/2" IMC or RMC
250.66 & table 250.66
2 x 600 = 1200 kcmil = 3/0 in 1"EMT GEC to the water service
#6 in 1/2 EMT, to the ground rod

Option 2) 800 amps
Table 310.15(B)(16) 75*C column
3-sets of 300 kcmil, 285 amps ech, = 855 amps.
Table C.1
3 sets of 4) 300 kcmil 2 1/2" IMC or RMC
250.66 & table 250.66
3 x 300 = 900 kcmil = 2/0 in 1"EMT GEC to the water service
#6 in 1/2 EMT, to the ground rod

Option 3) 1000 amps
Table 310.15(B)(16) 75*C column
3-sets of 400 kcmil, 335 amps ech, = 1005.
Table C.1
3 sets of 4) 400 kcmil 3" IMC or RMC
250.66 & table 250.66
2 x 600 = 1200 kcmil = 3/0 in 1"EMT GEC to the water service
#6 in 1/2 EMT, to the ground rod


The picture is my line drawing.
Thanks
MIke
 

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Must count the grounded conductor as a current carting conductor. So now you have four and must adjust.
600 @90 c 475 x 2= 950
950 x .80 = 760
So make you sure calculated load does not exceed 760
Most likely ok since you do have a 800 amp main.
 
Sorry about that worded poorly. I do not see how the high leg delta has a netutal since it one leg has a higher voltage to ground. It is not netutal to all three phases.
The grounded conductor will always carry current.
Please correct me if I'm wrong.
If I'm incorrect and it does not count please accept my apology.
 
Tulsa Electrician said:
I do not see how the high leg delta has a netutal since it one leg has a higher voltage to ground. It is not netutal to all three phases.
Click to expand...
It's still a neutral, just with a different voltage-to-ground on one phase.

Tulsa Electrician said:
The grounded conductor will always carry current.
Click to expand...
It will if any load uses it.

Tulsa Electrician said:
Please correct me if I'm wrong.
If I'm incorrect and it does not count please accept my apology.
Click to expand...
You're wrong, but there is absolutely no need to apologize. There would be if you refused to ask questions and learn.

A high-leg delta is a standard 1ph 120/240v source AND a standard 3ph delta source, superimposed on each other.

In fact, the high-leg, open-delta service originated as a modification to existing 1ph services for new equipment.
 
In a high leg delta, the grounded conductor does not carry any current for 3 phase loads, and acts like the neutral in a single phase 'split' system but only relative to the 'low' legs.

As such it only carries the unbalanced current of the 'low legs' and does not count as a current carrying conductor.

If anyone does something stupid such as use the 208V high leg to ground, then the fact that this grounded conductor is not a three phase neutral will rear its ugly head, the grounded conductor will not carry only unbalanced current, and will count as a CCC.

Jon
 
Tulsa Electrician said:
Must count the grounded conductor as a current carting conductor. So now you have four and must adjust.
600 @90 c 475 x 2= 950
950 x .80 = 760
So make you sure calculated load does not exceed 760
Most likely ok since you do have a 800 amp main.
Click to expand...
I was going to save this question for another thread but since you made this comment.
what do you guys think about me just installing a six throw panel as the main? If you have more than six throws you need a main. The six throw panel saves all the money for an 800 or 1000 amp main. Those are expensive and then you would still have to use some kind of panel board to split it up.
 
Avoid the GEC in EMT. You will need to bond each end. PVC sch 40 or if needEd Sch 80 if need physical protection. Sch 80 is considered equal to RMC
 
mike1061 said:
I was going to save this question for another thread but since you made this comment.
what do you guys think about me just installing a six throw panel as the main? If you have more than six throws you need a main. The six throw panel saves all the money for an 800 or 1000 amp main. Those are expensive and then you would still have to use some kind of panel board to split it up.
Click to expand...
Since the Chicago 2018 Electrical Code is the 2017 NEC with lots of amendments, you can still do a MLO with 6 service disconnects and no main. The service entrance conductors will have to have an ampacity at least equal to the calculated load, but do not have to have an ampacity equal to the sum of the ratings of the six service OCPDs.
 
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