3 Phase HVAC Units - Balanced Circuiting

[rmsc]

I have been in the AEC industry for many years, but admittedly I do not deal much with 3 phase electrical systems.

I am trying to get a handle on the circuiting of 3 phase mechanical units so that I have at least a minimal understanding of the work being performed by others. Specifically if those units need to be spread across 3 circuits in order to keep the circuiting balanced.

For example if I have 3 units (6500 watts each) could I put each unit on two circuits (total of 6 circuits) or would each unit need 3 circuits (total of 9 circuits)?

On a seperate note, is there any resource which would be helpful in understanding balanced circuiting for 3 phase power?

Thanks!

 

[augie47]

If I understand correctly, you have (3) single phase units to be placed on a three phase system. You are correct in the normal procedure would be to balance the system by placing 1 unit on phase A&B, the 2nd on B&C and the third on A&C simply by correct arrangement of the breakers. As you can see by the phase designation, each phase carries equal load.

 

[LarryFine]

RM, welcome to the forum!

For example if I have 3 units (6500 watts each) could I put each unit on two circuits (total of 6 circuits) or would each unit need 3 circuits (total of 9 circuits)?

The latter, if I understand your question correctly. Each piece of 3-phase equipment uses three hot wires, so each requires a 3-pole breaker, for a total of what you called "9 circuits."

It's actually three 3ph circuits. They're wired just like 240v 1ph circuits, even with a shared neutral sometimes, except with three hot lines instead of two.

On a seperate note, is there any resource which would be helpful in understanding balanced circuiting for 3 phase power?

Besides us? Blasphemy! :grin: I'm not really a resource kind of guy. But, 3ph loads are already as 'balanced' the same way that 240v 1ph loads alread are in a 1ph panel.

Your balancing goal would be for equal distribution of 1-pole and 2-pole loads the same way you would try to balance 1-pole loads between the two lines in a 240v 1ph panel.