Electrical equipment information different than circuit information

[Anonymous]

Revit 2012. Please refer to the attachments. HP-1 is a screenshot of the properties for panel HP-1. MSA-4 is a screenshot of circuit information for panel HP-1 back to the switchboard. The problem is this: the panel schedule, for total amps, is reporting parameters "Current Phase X" from the electrical equipment, which we believe to be incorrect. Circuit information for MSA-4, for total amps for HP-1, is reporting parameters "Apparent Current Phase X". These are the figures my engineer is expecting to see. FYI, Panel HP-1 has a 120/240 single phase xformer T-MBA connected to it.

My question is:

Why are these two figures different? Apart from creating a calculated value of our own in the panel schedule, we cannot make the Total Amps cell read a value from the electrical circuit information. It only accepts parameters from the equipment. So why are these two values, which Revit is calculating somewhere behind the scenes, different?

Thanks in advance to anyone that can offer some clues. We have spent half the day trying to solve this.

[Anonymous]

1. MSA-4 screen shot showing the ACP-X values your engineer wants to see inside that screenshot states that the ACP-x is on panel MSA? 

2. the screen shot you showed of the circuited panel states its panel HP-1

Q - so are you sure you are not just looking at the wrong panel? from what I read into this is that LOAD NAME HP-1 is on Panel MSA. If you goto your MSA panel you should see the ACP-x correct.

I might be wrong just thinking outload.

[CoreyDaun]

Here is a post from another forum by Martin Schmid, and may be related to your situation. Take a look....

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@Anonymous wrote:

The issue seems to be related to having your connector's Load Classification Parameter associated with a Parameter that has an empty value specified.

You can see in the attached video that when I create a Load Classification parameter, it has no value... when I then associate that with the connector, the connector ends up with a load classification with no value.  Thus, when you connect this, there is no value that propegates into the panel totals, since the panel totals are dependent on summing values from load classifications.  As soon as I set a value on the parameter associatd with the connector's Load Classification, the values tabulate.

You can see this demontrated and fixed in this video: http://screencast.com/t/OOLLMZh7K2vE

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[Anonymous]

I have uploaded new screenshots that are simpler to follow from a test model.

Thanks for the responses.CADastrophe, I looked into the post from Martin Schmid previously and I don't think it applies here. The problem isn't that a value isn't being propagated, it is that Revit is calculating a value differently for the panel than it is for the circuit (feeder) that feeds the panel. bwright, I think I understand what you are saying, but my original post may have been unclear, and my question still applies: shouldn't the amps per phase for the circuit feeding the panel be the same as the amps per phase on the panel? or put another way, on a switchboard, shouldn't the amps per phase for the circuit feeding a panel should be the same as the amps per phase for the panel? Refer to the screenshots. Shouldn't the amps per phase on MS 208 - 1 be the same as the amps per phase on Panel 208 panel schedule?

BTW, this discrepancy occurs using all OOTB settings. families, etc. as well. So I feel reasonably confident it isn't something in our template or families.

I have a panel with a 3 phase load and a single phase 2 pole load. Refer to Panel_208. The load for the entire panel is correct, as is the current. However, how it is calculating total amps per phase is what is wrong. (And I am not talking about whether it divides the load shorthand by L-G voltage or more mathematically accurately by RMS. ) This problem becomes more apparent as you add more load to the panel and especially if you had single phase two pole loads. I am not an engineer by training, but my engineers and designers tell me that the amps per phase is particularly important to consider in correctly sizing a panel. Granted, in my research thus far the amps per phase is always high rather than low, but it is still wrong.

For example:

8333VA/120V=69A (Load per Phase/L-G Voltage)=Amps per Phase OR (Load Phase*3/(208*sqrt(3))=Amps per Phase

If you select the panel, the properties display the current for phase A as 76A (screenshot Equipment). If you select the circuit (screenshot Circuit) from the panel to the switchboard, it displays the current for phase A as 69A. The load for phase A is the same for both. This is the root of the problem. The panelschedule only reports panel information, not circuit information, in this location on the panel schedule. If you look at Panel_208 you notice that I created rows for the correct calcuated values...for whatever reason that same forumula in the phase columns produces incorrect values as well.

In case I am not communicating clearly...amps per phase as calculated for the panel and shown in the panel schedule is different(and wrong) than what it calculates for the amps per phase for the circuit (correct) from the panel to whatever feeds it.

I will post over at AUGI as well and have made contact with other industry professional as well to try to resolve this. The next step may be to contact Autodesk. Thanks again for your help.

[Lance.Coffey]

I found the following blog post with information on how Revit is computing the per phase currents:

http://inside-the-system.typepad.com/my_weblog/2012/07/how-does-revit-compute-per-phase-currents.htm...

Also, a similar issue is described in the following blog post:

http://therevitkid.blogspot.com/2012/07/revit-tutorial-fix-electrical-panel.html

From what I have found, you can’t look at a single phase in isolation and assume that the current on that phase is the power divided by the line-to-neutral voltage. Due to the nature of 3-phase power, the computation is a bit more complex.

[Anonymous]

I am familiar with these blogs, the inside-the-system blog being most helpful and explanatory. When I found this I thought I had finally found an explanation. However, in his examples the math works out. In my example above it does not. I understand that to be completely accurate, one must use RMS (V*sqrt(3)) to calculate amps per phase. However, my engineers and designers tell me that using phase-to-neutral is industry accepted, simpler, and yields nearly the same result (which does seem to be the case).

Regardless, that is not the heart of the issue. I am looking for an explanation on why Revit is calculating amps per phase differently for the panel than it is for the feeder. As inside-the-system notes at one point: "...this is the current we see on Phase B and Phase C in the schedule, and is what we would measure on the feeders to the panel in an installation". This tells me that he believes amps per phase for the feeder and the panel should be the same, as do I. This is the heart of my issue: what Revit calculates for amps per phase for the panel is different than amps per phase for the feeder.

In my example above the discrepancy is 76A on the panel for Phase A and B, but 69A on the feeder for Phase A and B, or 6.46A. Comparing the two calculation methods, 8333VA / 120V = 69.44A. RMS is 8333VA * 3 / (208*sqrt(3))=69.39. This does not account for the difference. I received a reply to my post over at AUGI which, right or wrong, I believe explains the figures I am getting. 

Again, why are the amps per phase for the panel and the feeder to the panel different when they should be the same?

Any help is appreciated. If I sound frustrated that is because I am and I apologize but I am merely looking for a satisfactory explanation. 

[Anonymous · Accepted solution]

I have received an official response from Autodesk and consulted with our engineers and designers. In regards to the amps per phase reported on the panel schedules/panel, Revit is computing the values correctly. Refer to the 'inside-the-system' link above for a detailed explanation of the computations Revit is making. Conversely, dividing the VA by L-G voltage works fine on a balanced load but is not correct on a an unbalanced load, the error becoming more noticeable the more unbalanced the load is. This was an oversight on our part.

However, in regards to the root of my post, the amps per phase as reported on the panel being different than the amps per phase on the feeder circuit is a problem with Revit. I was told that this issue is now "being worked on by our developers for a future release."

Thanks to Lance from Autodesk for sticking with the case and hopefully this helps anyone else that runs into this problem.

[CoreyDaun]

Thank you for posting back here with your findings!