Increasing Service Size

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arnettda

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Am I on track here.
I have a existing building that is putting on an addition. My existing service is 200 amp 120/240 three phase. With historical data showing 25KW of load.
NEC2017 220.87 25Kw X 125%=31.25 KW amp
31250/240=130.20 AmpsX1.73=225.26 amps
Load calculation for new loads is 29KW all single phase loads.
29000/240=120.8 amps
225.26+120.8=346Amps would be my new service size?
 
arnettda said:
Am I on track here.
I have a existing building that is putting on an addition. My existing service is 200 amp 120/240 three phase. With historical data showing 25KW of load.
NEC2017 220.87 25Kw X 125%=31.25 KW amp
31250/240=130.20 AmpsX1.73=225.26 amps
Load calculation for new loads is 29KW all single phase loads.
29000/240=120.8 amps
225.26+120.8=346Amps would be my new service size?
Click to expand...
For the three phase calc, you divide by 1.732 not multiply. For the single phase new loads, I would say you did it correctly, but did you know you did it correctly? With a high leg Delta you probably want to assume no loads on the high leg, in which case you would just compute it as single phase and add that to your three phase currents. If you can equally balance the new single phase loads, then you would treat it as three phase current and divided by 1.732.
 
You should divide by 1.73, not multiply when calculating amps from watts.
You can also use this factor for your new single-phase loads as long as they’re 240V and distributed evenly across all 3 phases.
 
electrofelon said:
For the three phase calc, you divide by 1.732 not multiply. For the single phase new loads, I would say you did it correctly, but did you know you did it correctly? With a high leg Delta you probably want to assume no loads on the high leg, in which case you would just compute it as single phase and add that to your three phase currents. If you can equally balance the new single phase loads, then you would treat it as three phase current and divided by 1.732.
Click to expand...

You posted while I was typing!
 
electrofelon said:
For the three phase calc, you divide by 1.732 not multiply. For the single phase new loads, I would say you did it correctly, but did you know you did it correctly? With a high leg Delta you probably want to assume no loads on the high leg, in which case you would just compute it as single phase and add that to your three phase currents. If you can equally balance the new single phase loads, then you would treat it as three phase current and divided by 1.732.
Click to expand...
So I would take
3 phase 31250/240 =130.20 130.20/1.73=75.26amps

single phase 22000/240=91.66 amps

75.26A + 91.66A =166.92 amps for a new service size?
 
retirede said:
You should divide by 1.73, not multiply when calculating amps from watts.
You can also use this factor for your new single-phase loads as long as they’re 240V and distributed evenly across all 3 phases.
Click to expand...
Most of my single phase loads are 120 volt or either 120/240 so I would not be using the high leg phase. I was going to install a single phase panel along with my three phase panel feed off of one 320 amp meter socket. For future expansion.
 
arnettda said:
So I would take
3 phase 31250/240 =130.20 130.20/1.73=75.26amps

single phase 22000/240=91.66 amps

75.26A + 91.66A =166.92 amps for a new service size?
Click to expand...
It is not possible to have a 240V, three-phase, and 120V single-phase supply!
For a 3-phase configuration, you will either have: a) 120/208V (wye), b) 240V-delta (with 120V at center tap loads), or a 415/240V -wye with neutral (European).
On a 240V-delta supply, if your 3 phase loads are at 75.26A, and you have single-phase loads (@ 240V) is distributed on the three phases, (you can't balance a 22kW, single-phase loads on a three-phase supply), you will have to divvy up the 22kW loads--> 1-phase loads with 7kW on each phase plus a lone 1kW single-phase load.
My calcs here says you will end up with a full load of 133 amps. 75.18 A + 1.732(33 amps max phase amps) = 133A
If your loads were purely 3-phase, your full load would have been just 96A!
 
topgone said:
It is not possible to have a 240V, three-phase, and 120V single-phase supply!
For a 3-phase configuration, you will either have: a) 120/208V (wye), b) 240V-delta (with 120V at center tap loads), or a 415/240V -wye with neutral (European).
On a 240V-delta supply, if your 3 phase loads are at 75.26A, and you have single-phase loads (@ 240V) is distributed on the three phases, (you can't balance a 22kW, single-phase loads on a three-phase supply), you will have to divvy up the 22kW loads--> 1-phase loads with 7kW on each phase plus a lone 1kW single-phase load.
My calcs here says you will end up with a full load of 133 amps. 75.18 A + 1.732(33 amps max phase amps) = 133A
If your loads were purely 3-phase, your full load would have been just 96A!
Click to expand...

b21c1171a001ee82b8ef93184c265905.jpg
 
arnettda said:
Can you use all three phases for your 3 phase panel and then Phase A and C plus neutral for your single phase panel?
Click to expand...
For larger 4WD services, I like to use a 240V, 3Ø, 3W panel for all the 2-pole and 3-pole breaker loads with a separate 120/240V, 1Ø 3W panel for all the 1-pole breaker loads and any 2-pole breaker loads that have a neutral wire (like a pair of branch circuits with a shared neutral).

That way there's a better chance nobody will come along later and connect a "120V" load on the 208V wild leg.
 
retirede said:
B) is good. The first sentence seems contradictory.
Click to expand...
Yes the first sentence and b) contradict one another.

Though I get the point that you will not have ability to balance the 120 volt loads across the source without additional transformations, plus there is also possibility of having open delta source in which case you kind of have a 120/240 single phase supply anyway and then add whatever three phase load is on top of your other calculations, chances are that three phase load is pretty limited or if a major load is single larger load and the value is pretty fixed.
 
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