210.20(A) 80% rule - Main breaker

[designer82]

Does the 125% max rating for continuous loads apply to other than branch CB's?

Meaning can I load my Main CB for my service panel close to it's max rating? (Specifically, Got a 200A service 200A Main CB and after renovations, the new loading on the service will be literally 197Amps after a detailed loading calc.)

What are your thoughts? Too close for comfort or it's ok since it's below 200?

main-bkr-rating

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[Npstewart]

It’s 125% of continuous + 100% of non continuous. If you account for the continuous and non continuous loads in your service calc then your main breaker can be loaded up to its rating.


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[infinity]

197 amp load calculation is permitted on a 200 amp service. Also not every branch circuit breaker is limited to 80% of it's rating. Non-continuous loads can use 100% of the breaker rating.

 

[kwired]

This topic comes up somewhat frequently it seems.

I always say that the 125% for continuous loads for service/feeder calculations derived using art 200 doesn't apply unless otherwise mentioned.

Part of my reasoning is for loads that you can apply demand factors to, which is quite a bit of them in most dwellings, you must not have a true continuous load otherwise there would be no demand factor to be able to apply.

Take a look at the note at end of T220.12. It says the 125% is included in values in that table. Also keep in mind that table is more less the minimum load you need to calculate for lighting, you could have an actual load that is more or less.

220.51 says to use 100% of fixed electric space heating, however you must use 125% for selecting conductors and overcurrent protection for individual branch circuits.

Part IV optional calculations are even less specific on individual load items, how you supposed to pick and choose what is continuous and what isn't out of any that? I believe any continuous factor already considered in the process.

 

[designer82]

I did some more digging looking at articles 210,215,230

80% rule (continuous/non-continuous) applies to branch circuits OCPD's
80% rule (continuous/non-continuous) applies to Feeder circuits OCPD's
80% rule (continuous/non-continuous) Does Not apply to Service Equipment OCPD's

I believe this is the way

 

[kwired]

I did some more digging looking at articles 210,215,230

80% rule (continuous/non-continuous) applies to branch circuits OCPD's
80% rule (continuous/non-continuous) applies to Feeder circuits OCPD's
80% rule (continuous/non-continuous) Does Not apply to Service Equipment OCPD's

I believe this is the way

Many service disconnecting means are also the feeder OCPD for the load side conductors.

 

[JoeStillman]

For Article 220 Part III and Part IV, none of the service-calc loads are continuous (I confirmed this with NFPA). But that's only because they haven't discovered car chargers yet!

The resi service load calc will be 125% of the car charger + everything else.