kVA per Phase

[DMG_1]

Hi All.

I have a question regarding kVA per phase. If I have a single phase 208V load of 70A. Straight from the "Ugly's Book" --> kVA = (I x E)/1000 --> (70 x 208)/1000 = 14.560 kVA. Is this kVA per phase or is the per phase 14560/2 = 7280 kW? The same question can be posed for a 3-phase system. I am creating a panel schedule and need to put this information on the panel schedule. Thanks.

 

[GoldDigger]

Hi All.

I have a question regarding kVA per phase. If I have a single phase 208V load of 70A. Straight from the "Ugly's Book" --> kVA = (I x E)/1000 --> (70 x 208)/1000 = 14.560 kVA. Is this kVA per phase or is the per phase 14560/2 = 7280 kW? The same question can be posed for a 3-phase system. I am creating a panel schedule and need to put this information on the panel schedule. Thanks.

7.280 kW not 7280 kW!
The power dependent on each phase line will be the total kW of the load. But the product of the line current by the line-to-neutral voltage of 120V on the same wire, corrected for power factor, will not be equal to the load power until you sum the two.
The question is just what the information on the panel schedule is supposed to represent. Usually the intent is to be able to calculate the load current per line from the listed power value. Or else the total power on the panel by summing up the breaker values.
In your case you will be required to feed the line-to-line load from a two or three pole breaker, so that single multipole breaker will be supplying the full 14.56 kW, and two poles will be drawing 7.280 times 1.73 kVA but only 7.280 kW from the associated phase. If you are trying to calculate the load balance on the three phases, it gets more complicated than a simple panel schedule.

 

[Smart $]

Hi All.

I have a question regarding kVA per phase. If I have a single phase 208V load of 70A. Straight from the "Ugly's Book" --> kVA = (I x E)/1000 --> (70 x 208)/1000 = 14.560 kVA. Is this kVA per phase or is the per phase 14560/2 = 7280 kW? The same question can be posed for a 3-phase system. I am creating a panel schedule and need to put this information on the panel schedule. Thanks.

Here's the skinny of it...

When you sum a ? column (subtotal) then sum the subtotals (total), it should equal the kVA sum of all individual loads. What that amounts to, if your load is connected to one ?, its kVA is entered in the connected ? column. If your load is connected to two ?'s, one half gets entered into each column of the two connected ?'s. If your load is connected to three ?'s, one third gets entered in each ? column. It is the only way the total will be correct.

There are some misgivings about doing it this way when the ?'s are unbalanced... but as long as they are fairly balanced (say max deviation from average not more than 5%), the resulting determination of amperes per ? line will be accurate enough for most cases...