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

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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.
 

Ingenieur

Senior Member
Location
Earth
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

Senior Member
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

Senior Member
Location
Earth
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
 

Tony S

Senior Member
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

In = ±√((Ia²+Ib²+Ic²)-((Ia*Ib)+(Ia*Ic)+(Ib*Ic)))
 

kwired

Electron manager
Location
NE Nebraska
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

Senior Member
Location
Earth
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

Electron manager
Location
NE Nebraska
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

Senior Member
Location
Earth
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

Senior Member
Location
India
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
 
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