Existing Load on a Building

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Cliff Brady

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I am trying to figure out the load on the existing meter. The power company could not provide me any peak demand for the building, however they did tell me the max usage for the last 12 months. I was looking in section 220.87 and it states that I can either use the Max demand or I can take a measurement over a 30 day period. Is there a way to extrapolate the max usage to be a max demand? The max usage for the year was in February and it was 5939 kwh (240/1). Or is there another way to get the max demand?

Thanks in advance
 
The only problem is they want to start work as soon as possible. They have a 200 amp service and from that service, it serves 2 panels. Both panels having a 200 amp breaker. The building is so small and the load we are adding is so tiny, I don't think we really need the information, however, I know the building officials would like to see it.
 
Since the building is very small, you can do a field survey really quick. Go to the building, find out all existing electrical loads, add new loads, and do the electrical load calcualtion. You will find out if the existing electrical service needs upgrade or not.
 
Cliff Brady said:
Is there a way to extrapolate the max usage to be a max demand?
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Sorry, but there is not. All you can gain from "max usage" is a general idea of monthly average. But suppose the facility uses far less than average power for most of the month, and then has a couple very high usage days. The service size must be large enough to handle those high usage days plus whatever load you plan to add. So basing a decision on monthly average isn't allowed.
 
Cliff Brady said:
If I show that I am taking off more load than I am putting back onto the service, will this be acceptable?
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Don't suppose you can talk them (the building owners) into putting a 200 amp breaker between the meter and the panel taps, can you?
 
they (breakers) are already there. Each panel has a 200 amp breaker. The panel I am modifying, the breaker is outside with the disconnect and then the panel is a MLO. So even if I have the meter KWD, do I still need to monitor it for 30/28 days?
 
There is a chance that you can show by calculation per the code that you are below the requirement for the existing service. If you are below the requirements with adequate margin, you should be able to proceed.

The other possibility is that you will find that you are so close to or above the limit that you need a bigger service.

You can also do a test with an ammeter and a bunch of stuff turned on to see if you are close. I would do that after the calculation, and with the demand factors in mind.

A half day doing a walk-through survey and a load calculation should give you enough information to make a decision.

They don't require demand tests on a new building before it is built; they accept calculations. That should be good enough here.

You should be able to provide rationale for the high reading.
 
Cliff Brady said:
If I show that I am taking off more load than I am putting back onto the service, will this be acceptable?
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I have used that reasoning, and I have gotten approval from the AHJ. But I don't think there is any NEC article that would support use of this reasoning. So there is no guarantee that your local authorities would accept it. How about asking?
 
Thanks so much for your help. I contacted the AHJ and they said that they won't get too worried about the little we are adding.
 
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