Question on simple commercial drawings

[eeprom]

Hello,
I've spent most of the past 6 years doing industrial power distribution and controls. I've been asked to do load calcs and a panel schedule for a commercial remodel. I know this should be simple....but

The panel has about 24 breakers in it, 18 are already in use, and 4 will be used for the remodeling project. The building is very old, probably from the 1940s. There is no record of what the other breakers are used for. How can I do a load calculation without knowing the other breaker loads?

thanks
EE

 

[davidbeach]

Service records or apply a recording ammeter for a month.

 

[eeprom]

I can't imagine that a service record or an ammeter logger would be acceptable. If I were to go that route, I could just use 80% of each breaker and 100% demand factor. What I am wondering is, what is typically done under these circumstances?

 

[davidbeach]

Been there, done that, AHJ would accept either 30 days continuous monitoring or 1 year of utility records. Kind of matches up with what was in the NEC at the time (haven't done that kind of work for several years).

 

[eeprom]

Thanks. I don't have much else to go on. I could use the last year's average load to estimate the entire panel load. Then I'll have to lump all the existing breakers as equal to that load. The additional load would of course be the new breakers. I would have no way to balance the panel, but with the number of remaining breakers I don't see how I can do that anyway.

Thanks again for your help.

EE

 

[MiketheEngineer]

Hate to say this - but I have added breakers and just stood back and see what happened.

 

[eeprom]

I'll bet everyone who has ever worked in the field has done things like this. It's one of those things that's perfectly sensible to people who spend time in the field, and yet it seems insane to people who are tied to a desk.

 

[jmbelectrical]

NEC 220.87(1) requires that you use the maximum demand KW, obtained from the utility, over a time period of 1 year and 220.87(2) requires that you add 25% to this value. If utility data isn't available, there is an exception that permits the use of the maximum demand KW obtained over a time period of 30 days, as others have pointed out. If the panel in question is merely a subpanel in a much larger electrical distribution system, then you may have no choice but to record the usage for 30 days.

 

[eeprom]

jmbelectrical,
Thank you very much for that valuable code reference.