220-34 Optional Method - Schools

[jkim780]

Can somebody tell me how to use Table 220-34 for feeder and service loads calcs?

Thanks for your answer in advance.

[ March 18, 2004, 06:05 PM: Message edited by: jkim780 ]

 

[charlie b]

Re: 220-34 Optional Method - Schools

The first thing you do is to ignore the left-hand column. It?s metric. The next thing is to add up all loads in the building (i.e., lighting, power, water heating, cooking, and all other loads), but you only include the larger of the air-conditioning load or space-heating load. Then you divide the total VA by the total area (in square foot). Then you use the center and right-hand columns. Suppose for example that the total VA/ft2 was 30. You add the following:

3 VA/ft2 at 100 % equals 3.
17 VA/ft2 (i.e., from 3 to 20) at 75 % equals 12.75.
10 VA/ft2 (i.e., from 20 to 30) at 25 % equals 2.5.
Total VA/ft2 equals 18.25.

The last two steps are to multiply the 18.25 times the total square foot, to get the total VA, and then to divide by voltage, to get amps.

 

[jkim780]

Re: 220-34 Optional Method - Schools

Originally posted by charlie b:
Suppose for example that the total VA/ft2 was 30. You add the following:

3 VA/ft2 at 100 % equals 3.
17 VA/ft2 (i.e., from 3 to 20) at 75 % equals 12.75.
10 VA/ft2 (i.e., from 20 to 30) at 25 % equals 2.5.
Total VA/ft2 equals 18.25.

The last two steps are to multiply the 18.25 times the total square foot, to get the total VA, and then to divide by voltage, to get amps.

Hi, Charlie. Thanks for your reply. I am not sure if I understand you correctly.

Suppose my building is 82,000sf and my total VA/ft2 was 9. Then per table 220-34

3 VA/ft2 at 100% equlas 3.
6 VA/ft2 at 75% equals 4.5.
Total VA/ft2 is 7.5 VA/ft2.

So, 7.5 VA/ft2 * 82,000sf equals 615,000 VA.

Is that right?

 

[charlie b]

Re: 220-34 Optional Method - Schools

Yes. That is how I understand that table.