What is the definition of the "Maximum Phase Current"?
What is the definition of the "Maximum Phase Current"?
(OP)
Hello all
I am producing a One-Line and am asked to find the "Maximum Phase Current" based on all the loads on the circuit. In my case loads consist of some Transformer Rectifiers, several motors (all less than 10 HP), & some heaters.
I know HOW to find the Maximum Phase Current. My question is WHAT does it actually mean? What useful information would it give to, say, a customer who knows what it is?
I am producing a One-Line and am asked to find the "Maximum Phase Current" based on all the loads on the circuit. In my case loads consist of some Transformer Rectifiers, several motors (all less than 10 HP), & some heaters.
I know HOW to find the Maximum Phase Current. My question is WHAT does it actually mean? What useful information would it give to, say, a customer who knows what it is?






RE: What is the definition of the "Maximum Phase Current"?
If the load is unbalanced, one of the phases will have higher current than the other two, assuming a 3 phase source. The 3 phase source still needs to be sized based on the phase with highest current.
Say, the calculated load is 15, 10 and 10 amps on phase A, B and C respectively. The service has to be 15A, 3 Pole minimum or even greater based on local codes.
This also illustrates importance of balancing the loads, when all loads are not balanced 3 phase.
Rafiq Bulsara
http://www.srengineersct.com
RE: What is the definition of the "Maximum Phase Current"?
I'm being asked if the Max Three-Phase Current is for the "Connected Load". I'm not sure what this means. Any thoughts?
RE: What is the definition of the "Maximum Phase Current"?
You may also want to think if it is not for connected load, what else could it be for? You have all the information you would need for the calculations. (to calculate current in each phase). Do the exercise and see what numbers you get.
Rafiq Bulsara
http://www.srengineersct.com
RE: What is the definition of the "Maximum Phase Current"?
Another joker is the HP/kW without knowing the efficiency or power factor.
Sounds like homework. Not a real world application.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: What is the definition of the "Maximum Phase Current"?
Anyways sounds like no one can actually answer my original question, I will ask chief electrical guy tomorrow.
RE: What is the definition of the "Maximum Phase Current"?
Rafiq Bulsara
http://www.srengineersct.com
RE: What is the definition of the "Maximum Phase Current"?
Rafiq Bulsara
http://www.srengineersct.com
RE: What is the definition of the "Maximum Phase Current"?
Although it may not apply in your situation, if one load has a PF close to zero lagging and the other has a load of close to zero leading, the combined KVA may be close to zero and in any event much less than 58.9 KVA.
PF matters.
The maximum phase current is usually the maximum current that may flow in the most heavily loaded conductor under any condition of connected load. This does not mean all loads connected. If some loads are PF correction caps, maximum current may occur with the caps disconnected.
Phase loading may be phase to phase or phase to neutral. Maximum phase current may refer to maximum phase conductor current. This is used for sizing switch gear, conductors and protection.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: What is the definition of the "Maximum Phase Current"?