120/240 high leg distribution system

[abidalkareem]

Hi, 

So loos like Revit calculation engine can't correctly drive panel schedules for 120/240-3P High Leg system.

Is there is a way (other than Dynamo) to create an electrical distribution system that shows the correct phase and line currents in Revit ? 

[fabiosato]

Hello,

Which Revit version are you using?

[abidalkareem]

Revit 2025. 

[russellvee]

Are you actually using the high leg for 208V single phase circuits? Usually the 'B' phase is only used for 2 and 3 pole circuits. I'd probably just model it as a 4 wire delta with 120V L-G and assign spaces to 'B' phase. If you really need 208V branch circuits I'd model them as 120V and show panel loads in kVA so you don't have to worry about incorrect amps in the panel schedule. Or you could model a 120V-208V transformer for each high leg branch circuit. 

[abidalkareem]

I'm not using the high leg 208V single phase circuits. Revit internal calculation engine doesn't seem to be able to compute the phase and line current correctly for a 3phase delta. Panel schedules are showing a phase current that is greater than the line current. 

Showing the KVA's instead of the current is a solution I'll probably try. I'm not sure what the parameter.

Doesn't look like that Revit computes phase and line currents for delta any differently than a star. I don't know why those parameters are there in the Electrical settings. 

[russellvee]

Oh sorry, I was looking at R2024. I didn't realize they added a setting for the high leg phase in 2025. I'm not sure what the point is if it doesn't calculate amps on the high leg phase any differently. I'd still just blank off everything on 'B' unless you need multi-phase circuits.

[abidalkareem]

Not at all. The issue that I was trying to find a solution for is, when we create a 3 phase Y and specify that explicitly in the Electrical system, then the line and phase currents don't look any different if we change the configuration to Delta. In a 3 phase delta configuration the Line current must be greater than the Phase current. This is not the case here, and looks like the Delta/star revit parameter doesn't affect any change in calculations. 

[rosie_lucas1]

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[russellvee]

I tried to make an example to see if I understand your issue. I created a delta and star/wye system, each with (3) 1000VA 2-pole loads to account for phase loads AB, AC and BC. The load and calculated current are the same for each phase, but the line current is different by a factor of 240/208.

Revit doesn't calculate the phase current for loads AB, AC and BC. However, if I remove two of the three loads to have only the AB load remaining, it does calculate the phase AB current at 4.17A, which is 1000VA/240V. If you multiply that by sqrt(3) you get the 7.22A line current that it calculated for the balanced 3 phase load. 

For the high-leg system it doesn't seem to make any difference if you switch the high leg from A to B to C. If you model the same (3) loads as (6) single phase loads the results are the same. There doesn't seem to be any way to calculate if you have an imbalance between the 120V loads AG and CG without adding them up manually.

The delta/star setting certainly has an effect on the calculated values, and they look correct to me, but maybe I'm missing something.