panel balancing

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I am confused
208/120 3 phase

A local published book here with examples show
for 208 208 1phase loads that are in kw to multiply them by .577
For example
3000 watt water heater 3000 x .577 = 1731
A B C
1731 1731

15kw 208 outside lights 12000 x .577 = 8655

A B C
8655 8655

But in Mike Holt's book page 445 same parameters

he takes a 10kw water heater 208v and splits it
5000va on A phase 5000va on B phase. Which seems logical to me.

What am i missing somebody please set me straight. Thanks in advance. I am scheduled to take the Oregon Part 2 on may 3rd and from what little info I have it is a real bastard. Its one question 2 hours, all service requirements, transformer sizes, panel balancing, on a large commercial building. Then they call you back in 3 weeks to interrogate you on your methodolgy.
 

charlie b

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Location
Lockport, IL
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Retired Electrical Engineer
Re: panel balancing

Multiplying by the factor 0.577 is the same as dividing by the square root of three. I do not understand why this would come into play. Is the book calculating something other than just how much va to allot to each phase? Is it calculating current or something else, and does it then start dividing by a voltage value?

By the way, you used ?watts? and ?va? as though they meant the same thing. That is ok if you are talking about heaters, but it would not work with motors. I suggest always using va or kva.
 
Re: panel balancing

I agree with you, I used watts and kw because thats how they where written. This book is handmade printouts used in an IBEW contractor's class taught by an inspector.
In every example for coffee shop, bookstore, school, etc for 208 1phase loads rated in watts or kw he multiplied the watts by .577
after multiplying by 125% if continuous.

I am beginning to think this is wrong.
 

bennie

Esteemed Member
Re: panel balancing

Don't read things in the question that are not there. The author is considering unity power factor unless otherwise stated.
 
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