existing panel loads

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john37

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First I appologize if this is a stupid quetion...What is the best way to determine how much spare capacity is on an existing panel. If you just take a clamp on reading of each phase would you add up the reading on each leg and then divide by the voltage (e.g. A= 25.0 B= 27.0 C = 24.0 = 76.0/360 x 1000 = 211.1A Is this correct?
I know taking a clamp on reading isn't the best way to determine the load because of the peaks but if you want a general idea of how much power the panel is drawing (or how much spare capacity is on the existing panel) would this be a way to determine it? Any help would be appreciated. Thanks.
 
DanZ..Thanks but that wouldn't work because it's a distribution panel in a high rise office building. It's fed off the main switchboard. Sorry I wasn't clear enough on my explanation.
 
john37 said:
What is the best way to determine how much spare capacity is on an existing panel. If you just take a clamp on reading of each phase would you add up the reading on each leg and then divide by the voltage (e.g. A= 25.0 B= 27.0 C = 24.0 = 76.0/360 x 1000 = 211.1A Is this correct?
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No. This is not correct. You made a clip on reading and the avg amperage is about 25 amps. That the load on the panel at the time you took the reading.
Say the ampacity of the panel is 200 amps. Then you have about 175 amps spare. You need to take a recording amp meter and check the load over a long period during the peak month.
 
capacity

capacity

30 day load study. Fluke 1735 data logger is the way to go. Cost about 2500.00 to buy. Has many other uses also...
 
existing panel loads

if its a big load your are going to add to it just simply do a load calculation and you can not go wrong 3 va per square foot since its a residential dwelling then go to the section 220
 
To be more specific I'm trying to add to the load on the existing distribution board. RIght now there is an existing 400A 480/277V, 3Ph, 4W with a 3P200A main. I took a clamp on reading and it read A: 30.6 B:50.8 C:25.0 N:21.7
I need to determine if we can add another panel to this board and if so how much more spare capacity the existing distribution board currently has on it. I don't have the luxury of doing a 30 day load study as the owners want to take over addtional tenant space in the building. I would love to do the 30 day study, but I'm just trying to figure out if it's even a possibility or should I look for an addtional power source. Thanks...
 
john37 said:
I don't have the luxury of doing a 30 day load study as the owners want to take over addtional tenant space in the building.
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The choice is not theirs to make. If you wish to add load to an existing facility, there are three ways to determine if there is spare capacity. In your case, one of them (utility records) is not going to help. You can list all existing loads one by one, and add them up, or you can do a 30 day load study. Taking a few sample readings can certainly give you a rough idea of whether the 30 day load study will produce a favorable result. I have also had cases in which the AHJ allowed the addition of load during the time that the 30 day load study was in progress, pending final approval of the calculation that includes the 30 day load study.
 
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