Parallel / Series Question

[cooltc2004]

This isn't your typical parallel / series question. Engineers before me designed our heating element boxes a certain way, and I'm not sure why they did it.

Its a bank of heating elements run off of 480VAC / 1 Phase power. It was designed with 240VAC 1625W elements, run in a parallel/series configuration (bottom configuration on the attached image). This unit is advertised as 19.5kW, but I'm getting half of that if I'm looking at it correctly. I want to run 480VAC 1625W heating elements in a parallel configuration (top on attached image).

Any thoughts or ideas on why it was configured as it was? Am I missing something?

(Notes on drawings: there are 12 heating elements in each box, #1 on the top is the same element as #1 on the bottom. The elements contained within a box are connected via a busbar. A1 and B1 are from a single contactor, A2 and B2 are a separate contactor. This allows us to run this unit at half power.)

 

[Smart $]

((3+3)×2) elements × 1625W@240V/element = 19,500W

(6×2) elements × 1625W@480V/element = 19,500W

???

Perhaps it was configured that way just in case only 240V was available.

 

[cooltc2004]

((3+3)×2) elements × 1625W@240V/element = 19,500W

(6×2) elements × 1625W@480V/element = 19,500W

???

Perhaps it was configured that way just in case only 240V was available.

They're both run @ 480V, so wouldn't you not multiply by 2 in the top equation and run them in series to get 480V?

 

[Smart $]

They're both run @ 480V, so wouldn't you not multiply by 2 in the top equation and run them in series to get 480V?

One set of 3 elements @240V in series with another set of 3 elements... powered with 480V, which is 240V to each set of 3.

 

[Jraef]

Running them in series changes the watt density (W/square inch of surface are), which, if you are concerned with scorching something, becomes important

 

[Smart $]

Running them in series changes the watt density (W/square inch of surface are), which, if you are concerned with scorching something, becomes important

The diagram makes me believe the physical number, size, and position of the 240V vs. 480V elements are the same. And each element is 1625W regardless of voltage. So the watt density appears the same either way.