New service based on previous design historical data

T

That Man

Senior Member
Location
California, United States
Occupation
Electrical Designer
Is there guidance in the NEC, or IEEE color books, or some other U.S. code that addresses this scenario? Client is installing a new industrial facility system. They have detailed historical data from the same design installed elsewhere, and would like to size the new service based on that historical data instead of using connected load numbers. I thought there was an exception or FPN in the NEC that addresses this, but I'm not seeing it.
 
ron said:
In the NEC 2026, you are thinking of section 120.87 for existing installations. In previous versions it was 220.87
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The sticking point I'm running in to is the specific language (bold by me):

The calculation of a feeder or service load for existing installations shall be permitted to use actual maximum demand to determine the existing load

This is a new installation. I don't see anywhere where it is stated that historical data from an existing installation can be applied to a new installation. Even though it makes perfect logical sense, if it doesn't say it, it could be argued it doesn't apply. I thought there was a note or exemption somewhere that states this explicitly.
 
Most industrial facilities are designed under engineering supervision and don't use the provisions of Article 220 (now 120 in the 2026). The code does not provide for this, but likewise the code has no real provisions for calculating the load in an industrial facility.
 
don_resqcapt19 said:
Most industrial facilities are designed under engineering supervision and don't use the provisions of Article 220 (now 120 in the 2026). The code does not provide for this, but likewise the code has no real provisions for calculating the load in an industrial facility.
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I'm operating under this very same assumption. This facility is designed under engineering supervision. I just can't find any language anywhere that says this. Is there language somewhere in a code that states that under engineering supervision, Article 220 does not apply?
 
I had a commission once where the owner was consolidating three factories into one new one. I used the demand histories of the three old facilities. My load estimate was validated a year after. If we had used the connected loads, it would have cost a fortune for wasted capacity.

Making railroad car axles takes a different demand factor than ball point pens, but it's the same CNC machine.
 
I sure wish there was some code language somewhere, anywhere to back up what I've always known as standard practice. It makes it feel risky as a consultant to suggest it as a strategy if an AHJ somewhere can challenge it and I have no basis. Just sayin
 
That Man said:
I sure wish there was some code language somewhere, anywhere to back up what I've always known as standard practice. It makes it feel risky as a consultant to suggest it as a strategy if an AHJ somewhere can challenge it and I have no basis. Just sayin
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If you paste a real nice spreadsheet on the page with your SLD, you'll get a TLDR from the plan reviewer, just like your specs.

Article 220 refers you to other parts of the code before it gets into all the nitty gritty calculations. I especially like where 220.3 points you to 430.26 for feeders (and services) with motors on them.
 
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