Load center

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kalanjeya

kalanjeya

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chennai
There is a big clash between our US client and me(In India) regarding load calculation .please help me out which is correct.

There is a 120/208V system

8 nos (8x800W)of single phase outgoing feeder.

1 nos of threephase outgoing feeder (4.5kw)

How will you size the incomer here?

a)


A ### B ## C

800 ##800 ##800
800 ##800 ##800
800 ##800 -
1500 #1500 #1500
-----------------------------------
3900 #3900 #3100
-----------------------------------

So the incomer will be based on the total load

3900+3900+3100= 10900 / 1.732*208 = 30.25A



( OR )


b)


A ### B ## C

800 ##800 ##800
800 ##800 ##800
800 ##800 -
4500 #4500 #4500
-----------------------------------
6900 #6900 #6100
-----------------------------------

So the incomer will be based on the maximum load

on the any phase like A (or) B

6900 / 1.732*208 = 19.15 A


Please help me out.

Jeyakumar
 
Re: Load center

Are your 800 Watt 1? loads 120 Volt or 208 Volt? You seem to be showing 800W @ 120V in both (A) and (B).

What is the size of the total load on the 3? feeder? You seem to be showing 4500W in (A) and 13.5kW in (B).
 
Re: Load center

Are your 800 Watt 1? loads 120 Volt or 208 Volt?

--------IT IS 120v

What is the size of the total load on the 3? feeder? You seem to be showing 4500W in (A) and 13.5kW in (B).

THAT IS WHAT MY QUESTION , WHICH IS THE CORRECT WAY OF INDICATING THE THREEPHASE LOAD IN THE LOAD CENTER AS WELL AS CALCULATING INCOMER.

THANKS FOR YOUR QUERY al hildenbrand .
 
Re: Load center

Your picture is not very clear.

I think you are trying to show 8-800watt single phase loads and 1-4.5 Kw 3 phase load. Is this correct?
 
Re: Load center

Could you use the amperages of the loads and eliminate the confusion? 4.5 kW balanced 3phase load would load each phase 1.5kW. Use amperages to make sure what is described as 4.5kW 3 phase outgoing feeder is just that, and not really 13.5 kW.

In the second example where you derive maximum amperage on one line, you do not use the 1.732 factor there, only the kW (kVA really) and the voltage line-N. If you have a 3 phase load (assumed to be balanced) you will use the equation in the first example.

edited to add to post because I didn't notice the problem with equation in the second example at first.

[ January 06, 2006, 10:37 PM: Message edited by: ccjersey ]
 
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