Hello,
Here is a post titled "panelboard - calculations..."
Charlie B explains how in a 3PH panel you take the load and Always use units of power (KVA) to get total load and that you never add amps from one phase to another as sometimes this can lead to errors since the current has a phase angle associated with it and that is different between phases.
I have 2 questions regarding this:
1. The OP in that thread asked the good question of (paraphrasing) "well if you can't add current from one phase to another because of the angle, wouldn't you get the same issue with power since it is S=VI." Charlie B said it was a complicated answer but ultimately the math works out that you can add KVA from one phase to the next since the power in the 3 Phases when added is a constant number since the Time variable is lost.
What about adding current from one "phase" to another in a single phase (split phase) panel? Why would you still be able to add the power from one phase to another but not current? Single phase power does have a time variation associated to it. How does the math work out? How would Charlie B answer the OPs question if it were a single phase (split phase) panel?
2. When running the risk of calculating an error when adding amps between phases instead of KVA, does the potential error come solely from the 2 below sources?
a. Current in one phase is at a different phase angle than current in the others.
b. In all the threads regarding this the 2 pole loads seem to come up as a culprit and a possible location of error. It seems to be because if you don't use KVA than you won't be able to split the load on two different phases.
Lets say you don't have 2 pole loads, can currents be added then if Phase angle is taken into consideration?
Here is a post titled "panelboard - calculations..."
panelboard calculations...
I need some help answering the question "what is the load on this panelboard?" This example panelboard is fed by a 208Y/120v xfmer and has 3 simple loads: 1) 208v, 3 phase, 2000W fed from 3 pole breaker 2) 208v, 1 phase, 1000W fed from 2 pole breaker on phase A and B 3) 120v, 1 phase, 500W fed...
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Charlie B explains how in a 3PH panel you take the load and Always use units of power (KVA) to get total load and that you never add amps from one phase to another as sometimes this can lead to errors since the current has a phase angle associated with it and that is different between phases.
I have 2 questions regarding this:
1. The OP in that thread asked the good question of (paraphrasing) "well if you can't add current from one phase to another because of the angle, wouldn't you get the same issue with power since it is S=VI." Charlie B said it was a complicated answer but ultimately the math works out that you can add KVA from one phase to the next since the power in the 3 Phases when added is a constant number since the Time variable is lost.
What about adding current from one "phase" to another in a single phase (split phase) panel? Why would you still be able to add the power from one phase to another but not current? Single phase power does have a time variation associated to it. How does the math work out? How would Charlie B answer the OPs question if it were a single phase (split phase) panel?
2. When running the risk of calculating an error when adding amps between phases instead of KVA, does the potential error come solely from the 2 below sources?
a. Current in one phase is at a different phase angle than current in the others.
b. In all the threads regarding this the 2 pole loads seem to come up as a culprit and a possible location of error. It seems to be because if you don't use KVA than you won't be able to split the load on two different phases.
Lets say you don't have 2 pole loads, can currents be added then if Phase angle is taken into consideration?
