sizing the power for different conduit /distrib scenarios for 3phase or single phase

[wyreman]

Should I run single phase 208 loads from nearest subpanel or bring a new 3phase panel to the idf room from the main.
I can hear the shouts... "Bring a new panel from the main"
I have to show the cost benefit of each.


I understand load balance and 3phase distribution. it's the calcs for the 1.732 part that I dont remember.
I do know the run is short, less than 30'! =) And the source panel is crowded.

If I run three 16a loads single phase 120v*16a*3cts =total of 5.76kVA avail to run those little loads.
Same with three 16a loads single phase 208v * 16a*3cts = total of 10kVA [ using 6 breakers instead of 3]

now three phase 30a which i would think gives me more gives
208v*24a*1 ct or 5kVA with three breaker slots.
but wait... what about the 1.732... and the power factor [call it one with the 2015 rectifier battery inverter] - so does the 30a 3pole makes 8.7kVA available to split off into single phase loads -
This becomes more interesting when the 60a distribution is set up there and would provide 17.3kVA to be split off. that's alot of 1.9kVA "20a cts"

so is that the proper application of the square root of three here? pythagorean case of the half height hyotneuse

In general I'm just trying to size how many wires I can get into an exis conduit most efficiently
I need to know here the difference is power use between the three phase and the single phase.
Also the ups come in 3phase 30a variety... i need to compare that to the nameplate amps available to drive 20a 208 single phase -
==>jam the most conductor size and quantity to drive the most batteries in a 3/4" emt for 30' and recommend which way to go w the ups
30a 3phase or more 20a single phase... or just bring a new sp and distribute it all from up there.

I can add up nameplates and size them to 80% and recognize a wild leg =0
Here I'm trying to come up with different scenarios for different conduit size and distribution.
I'm stuck on the square root of three :/
:slaphead:

 

[iceworm]

Should I run single phase 208 loads from nearest subpanel or bring a new 3phase panel to the idf room from the main.

... I understand load balance and 3phase distribution. it's the calcs for the 1.732 part that I dont remember.
... Here I'm trying to come up with different scenarios for different conduit size and distribution. ...

Hopefully this example applies to what you are asking. It is a bit simplistic and I highly suspect you already know all of this.

Consider 4 - #8 in a conduit.

Connect as 208V, 3phase, 4W (Fourth wire is a neutral). This will give you 3 each 120V, 50 A circuits. The circuit can deliver 3 x 120V x 50A = 18kva. Also can be calculated as three phase power: sqrt(3) x 208 x 50 = 18kva

Now consider using the same 4 conductors, two 120V, 1 phase circuits connected to the same 208 panel. Can't common up the neutrals cause that would over load the common neutral. (Forget the derate for now)The circuit can now deliver 2 x 120 x 50 = 12kva

ice