on a 120/208V panel with all loads 120V,why total amps is calculated on 208V base?

[peterwire]

I have a panel where all the loads are 120V 1-pole CB, but the panel itself is 3ph, 4w. Once i calculate the VA per phase, and the total VA, why should i calculate the total current: total VA/(208*1.732) instead of total VA/(120)? all the CBs in the panel are 1-pole.
thank you.

 

[jumper]

The math comes out the same.

3 x 120 = 360

208 x 1.732 = 360

6 of one or a half dozen, assuming your loads are correct.

 

[Ingenieur]

because although each load is single phase the combination is 3 phase

spaces 1 3 5 = ABC... spaces 2, 4, 6 + ABC, and so on
a load on A-N and B-N is actually a load A-B
a load on B-N and C-N is actually a load B-C
a load on C-N and A-N is actually a load C-A

if balanced = 0, if not resultant flows in neutral

 

[jumper]

because although each load is single phase the combination is 3 phase

spaces 1 3 5 = ABC... spaces 2, 4, 6 + ABC, and so on
a load on A-N and B-N is actually a load A-B
a load on B-N and C-N is actually a load B-C
a load on C-N and A-N is actually a load C-A

if balanced = 0, if not resultant flows in neutral

How did the noodle (neutral) load come into calculating a service load?

Sizing the noodle, yes. Sizing the service load, nope.

 

[Ingenieur]

How did the noodle (neutral) load come into calculating a service load?

Sizing the noodle, yes. Sizing the service load, nope.

he asked why on a 208 (3 ph, 1.732) basis rather than 120 (single ph)
I explained because the single phase add to 3 ph loads, ABC, not AAA
just a comment that if balanced, 0 N, if not something
not specifically for sizing but concept

 

[jumper]

he asked why on a 208 (3 ph, 1.732) basis rather than 120 (single ph)
I explained because the single phase add to 3 ph loads, ABC, not AAA
just a comment that if balanced, 0 N, if not something
not specifically for sizing but concept

Okay, I got it.

 

[Tony S]

because although each load is single phase the combination is 3 phase

spaces 1 3 5 = ABC... spaces 2, 4, 6 + ABC, and so on
a load on A-N and B-N is actually a load A-B
a load on B-N and C-N is actually a load B-C
a load on C-N and A-N is actually a load C-A

if balanced = 0, if not resultant flows in neutral

I_n = ±√((I_a²+I_b²+I_c²)-((I_a*I_b)+(I_a*I_c)+(I_b*I_c)))

 

[kwired]

a load on A-N and B-N is actually a load A-B
a load on B-N and C-N is actually a load B-C
a load on C-N and A-N is actually a load C-A

You have to be balanced on all three phases or there is load on the N.

In a wye connected system if A load on A-N and B-N has load current on A, B and N even if A and B are the same current.

If you have same current A-N, B-N and C-N then the N's carry current up until they become a common point, after that current from A is returning to both B and C and same with the other two.

 

[Ingenieur]

You have to be balanced on all three phases or there is load on the N.

In a wye connected system if A load on A-N and B-N has load current on A, B and N even if A and B are the same current.

If you have same current A-N, B-N and C-N then the N's carry current up until they become a common point, after that current from A is returning to both B and C and same with the other two.

That is what I said
if balanced = 0
if not, not 0

 

[kwired]

That is what I said
if balanced = 0
if not, not 0

I didn't feel it was all that clear to those that may not understand as well that balanced means all three phases must be the same.

If you have same current A and B you still have neutral current, unlike when you have a 180 degree phase angle on single phase or on just one side of a delta system.

 

[Ingenieur]

I didn't feel it was all that clear to those that may not understand as well that balanced means all three phases must be the same.

If you have same current A and B you still have neutral current, unlike when you have a 180 degree phase angle on single phase or on just one side of a delta system.

in any power text one one of the first subjects is balanced 3 phase systems
math is easier
the onto unbalanced

Loads on A and B
what if the load ratio is Za/Zb = -1/-120deg

 

[Sahib]

I have a panel where all the loads are 120V 1-pole CB, but the panel itself is 3ph, 4w. Once i calculate the VA per phase, and the total VA, why should i calculate the total current: total VA/(208*1.732) instead of total VA/(120)? all the CBs in the panel are 1-pole. thank you.

If loads are balanced only i.e equal in each phase, you may apply that formula. Otherwise you have to calculate current individual. phase wise