Filling Out Panel Schedules

[Smart $]

Wow. Great graphics Smart$! Thanks for that. What did you use to create that? I tried to paste an ACAD drawing but it didn't turn out.

The vector graphics were created in TurboCAD. However, TurboCAD does not have an anti-aliased display (as does AutoCAD). To clean it up for screen display I print the drawing via Adobe PDF then do screen capture (Print Screen) of it opened in Acrobat. From there I paste it in Canvas, crop the image, then save it in GIF format.

 

[Smart $]

Even with the fancy graphics it's still 9 amps either way. BTW: The guy in field doesn't have the fancy graphs!

Yeh, but he may have an amp clamp :wink:

The point is: the panel schedule KVA method mentioned above is not as accurate as one might think.

 

[sceepe]

Single pole (1? L-N) and [balanced] three pole (3? L-L-L) load currents are in phase with line-to-neutral voltage (resistive-only circuits). Two pole voltages and currents are, however, 30? out of phase with line-to-neutral voltage...

Smart$,
While I agree your method gives a more accurate measure of the currents per phase I really think it is irrelevant.

First, who cares what the currents per phase are? The OP was trying to use a program to size a panel or a main breaker. What really matters is that you get the total 3 phase VA added up correctly and correctly convert this number to amps.

Second, even with your method, you have to assume the power factor for each load. This information is never known during design so all you can do it get close anyway. Why go to all the extra effort to get to a answer that is 0.5 amps more accurate when your basing it on an assumption anyway. You may have already addressed this when you said:

The problem, perhaps trivial in some eyes, is using this method can give an appearance of having a balanced panel... yet it is not.

I have no doubt that your point is valid. However, no matter how you look at it, when you are designing a distribution system for a building, you have got to make some assumptions. After all, the spreadsheet the OP was trying to make is a calculator not an accurate model of the building's electrical system. In my opinion, if you try to convert all your loads to amps, and then add up single pole amps with 2 pole amps, with 3 pole amps, your much more likely to screw it up.

 

[Smart $]

Smart$,
While I agree your method gives a more accurate measure of the currents per phase I really think it is irrelevant.

I too see it as being irrelevant as the KVA panel schedule method is not likely to change in the near future.

First, who cares what the currents per phase are?...

Well apparently anyone that makes up such a panel schedule cares... but KVA is used in leiu of amperes to balance the currents. Using KVA does not change the fact that balanced current is the goal.

The OP was trying to use a program to size a panel or a main breaker. What really matters is that you get the total 3 phase VA added up correctly and correctly convert this number to amps.

...And the total amperes is divided equally among the three lines, regardless of the fact that current on the three lines may have an imbalance. In addition, this does not account for continuous and non-continuous loads, nor does it include demand factors, all of which have bearing on determining panel size, main breaker, and feeder size... then we get to the fact that none of these are rated in KVA units. In typical designs, transformers are the only piece of equipment with a KVA rating.

Second, even with your method, you have to assume the power factor for each load. This information is never known during design so all you can do it get close anyway. Why go to all the extra effort to get to a answer that is 0.5 amps more accurate when your basing it on an assumption anyway. You may have already addressed this when you said:

The problem, perhaps trivial in some eyes, is using this method can give an appearance of having a balanced panel... yet it is not.

I do not dispute what you are saying, but the fact is, unless one is careful, the difference could amount to more than 0.5 amps... it could just as easily be 5 or 50 amps, and without careful scrutiny may cause a blunder in the eventual sizing. I understand that most are careful in the design, but it's no wonder NEC sizing criteria includes an extra 25% margin.

I have no doubt that your point is valid. However, no matter how you look at it, when you are designing a distribution system for a building, you have got to make some assumptions. After all, the spreadsheet the OP was trying to make is a calculator not an accurate model of the building's electrical system. In my opinion, if you try to convert all your loads to amps, and then add up single pole amps with 2 pole amps, with 3 pole amps, your much more likely to screw it up.

Well I wouldn't screw it up, but I do believe some others are likely to

 

[hardworkingstiff]

......

Well I wouldn't screw it up, but I do believe some others are likely to

LMAO!!!!!:grin: