ADDING UP ALL 3 PHASE CURRENT IN A PANEL SCHEDULE?

[EEAOC]

I have an Architect disagrees with me that adding up all three phase currents at the bottom of a panel schedule will total up to the size of what ever panel size.
Can some one clarify this to me?

Also recent reading taken by an Amp -probe in all three phase feeders in a 400 Amp panel adds up to 470 Amps. I am not sure how this is possible?
Thanking you in advance.

EEAOC

 

[jghrist]

The panel size is amperes per phase not the total of all three phases.

 

[rbulsara]

If this helps to understand better, A 3 phase, 400A panel is rated to carry '400A' in EACH of the three lines (phase feeders, the term you used).

It is a different matter that Code requires not to load a panel more than 80% of its rating unless it is listed for 100% use. (using 100% rated breakers).

 

[cuky2000]

The ampacity rating of the panel should be based on the maximum phase current. When the three phase current are added, the phase angle should be considered. The result total current will be small or almost close to zero for balance system without significant amount of harmonics.

 

[light1]

The maximum phase current should be used for the panel sizing. Some panels are sized for 100% of the phase current others for 80% of the maximum phase current, depending on the panel and main circuit breaker or switch load rating. It is a good design practice to provide some spare panel capacity for the future load growth.

 

[wareagle]

Breakers are rated for 100% of its listing for noncontiguous loads(3 hrs or less).
If the load exists for more than 3 hrs the rating must be reduced to 80% of the breakers name plate listing.

 

[advidana]

It like with three computers each one can be used at the same time. but one computer is not three computers.

 

[wilkin]

A 3 PHASE 400 AMP BREAKER CAN CARRY A MAXIMUM OF 400 AMPS IN EACH PHASE.
THERETICALY FOR A BALLANCED LOAD AS EACH PHASE IS 120 DEG APART THEY AD UP TO ZERO.

 

[rbulsara]

wilkin:

That zero sum is is only for the summation of currents in the neutral (for fundamental frequrency currents). That does NOT amount to zero power.

400A in three phases is equivalent to 1200A single phase current in terms of power consumption.

Total power for a 400A, 3-phase system is 1.732*V*400*pf where V is line to line. Which equals (3)*(V/1.732)*400*pf or 3 times the 1200A*single phase voltage.

 

[peebee]

Don't feel bad, EEAOC. I've met at least one other computer guy that wanted to add up voltages. He had about 50 pieces of equipment running at 120v, so he figured he needed 50x120 = a 6kV system. This really happened.