Reducing Existing Service Size

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philly

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I have another question here related to service entrance to help round out my understanding related to modifications of existing services (figured I'd keep topics as separate posts).

For existing 480V commercial services are there any requirements or limitations for reducing the existing service size as part of a system modification? The only requirement I would think would apply here is that of 220.87 in determining existing loads and then re-evaluating service size (for increase or decrease) based upon evaluation of existing load profile.

Let me give an example....

An existing commercial distribution facility originally had a 4000A main switchboard installed with service entrance conductors rated for 4000A. The existing utility service transformer is a 2500kVA transformer (3007A secondary) and we know that utility does not have to adhere to NEC load calc requirements and just has liberty to supply whatever size transformer they determine adequate based on information.

Now lets say as part of a project the existing service entrance switchboard and service entrance cables are going to be replaced. The question comes up from a cost saving standpoint if that service can be reduced to a 3000A service as part of the new project? To me the answer to that would be based off determining what the existing load profile is. For example if we had a years work of utility bills for this service that showed that the maximum load for this service was 2100A then following 220.87 you'd identify existing load profile as 2625A (inclusive of 25% multiplier in 22.87). Is this enough to justify a reduction in service size or are there other considerations here?

Perhaps the above may not be the best example if the numbers are close but I think it illustrates the point hopefully. A more extreme case here would be a 1000kVA utility transformer on a 4000A service.
 

Hv&Lv

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I would never base any service size from a utility transformer.

That 2500kVa in your example is plenty big for a 4000 amp service. Your numbers are calculated at XF 100%. That transformer is fully capable of doubling that ampacity for a time depending on duration and ambient temp.

I would also caution against that article with the years demand. If you are using that for a big project the numbers (new equipment - equipment removed) have to be kept up with very carefully when changing out big machinery.

Utilities keep up with demand for billing and transformer sizing to reduce system losses. The goal is to make sure every transformer is operating at full capacity. (No load watts vs full load watts)
 
Sure, there is nothing wrong with lowering a service size when doing an equipment upgrade, if you don't need the previous capacity. A couple times I changed out a 2000 amp switchboard and put in a thousand amp panel board for cost savings. In those cases the switchboard service disconnect and SEC was a thousand amps so the service size remained pretty much the same so that's a little different than what you're talkin about.
 
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