480/240 current calculation

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dm9289

Industrial Maintenance Electrician
Location
Pennsylvania
Occupation
Industrial process repair/ maintenance Electrician
I have a heating system powered by a 480v open delta

It feeds 3 step down 480/240 transformers that feed 3 separate heating grids

phase a-b grid 1, phase a-c grid 2, phase b-c grid 3

each grid draws 600amps at 240v, it is an on/off circuit no variable control

How can I calculate an approximate current that will be drawn on each leg on the 480v side?
 
dm9289 said:
I have a heating system powered by a 480v open delta

It feeds 3 step down 480/240 transformers that feed 3 separate heating grids

phase a-b grid 1, phase a-c grid 2, phase b-c grid 3

each grid draws 600amps at 240v, it is an on/off circuit no variable control

How can I calculate an approximate current that will be drawn on each leg on the 480v side?
Click to expand...
When both adjacent grids are on:

Where just the 480V 1? primary, 300A@480V (half what's on the 240V secondary side).

Where combined:

300A ? sqrt(3) = 520A@480V 3?
 
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To explain better each of the 3 grids are current clamped one leg to a meter

each grids meter at 240v will read 600amps

all three grids come on at same time
 
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