sizing a service

[mshields]

After going through all the rules in Article 220 for a residential multiple condo unit building, I typically take what ever value I get and multiply it by 1.25. Strictly speaking, per the code, do I need to do that. e.g. if my calc comes out at 390Amps, I would not use a 400A service but bump it up to the next standard size or 600A. Am I being overly conservative and strictly speaking what does the code say about this?

 

[augie47]

NEC 90.1 & 90.8 remind you that the Code is a minimum requirement to safeguard persons and property from hazards.
It does not address future expansion, etc. Your multiplier certainly might be appreciated by the customer at some point but will also keep you from being low bidder.

 

[Smart $]

Code says you only have to multiply the continuous portion of the load by 125%... and there is seldom any significant continuous load in residential. With load calc's commonly reported as being overly conservative compared to actual load, a 400A service for a calculated 390A load should suffice... until someone adds 11A more of load under Code.

:slaphead:​

 

[Ingenieur]

How many units
sq ft/unit
???

 

[electrofelon]

After going through all the rules in Article 220 for a residential multiple condo unit building, I typically take what ever value I get and multiply it by 1.25. Strictly speaking, per the code, do I need to do that. e.g. if my calc comes out at 390Amps, I would not use a 400A service but bump it up to the next standard size or 600A. Am I being overly conservative and strictly speaking what does the code say about this?

If you do your calcs the "normal" way, the 125% for continuous loads is already factored in. Whether to go beyond the load calc is a judgement call based on a number of factors such as if you are bidding against other people, the type of structure and use, cost, etc. One philosophy that I have used is that if more capacity is needed later, at that point you could likely use ye old 220.87 and suddenly find yourself with a bunch more free room :happyyes: