Non- Dwelling Unit Calculations for a Service and Rating of Service Disconnect

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Sparky2791

Sparky2791

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Northeast, PA
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Electrical Design
Good Evening fellow Sparky's

First -

NEC 220.40 and 230.79 Both basically say use Part II of 220 to calculate the service size. Article 220 Part II does not include anything about only the larger of the 2 loads heating or air conditioning for a non-dwelling unit being included as part of the service loads.


220.18 (A), makes no sense to me, can someone explain?


Second -

Part II of article 220 says nothing about needing to use 125% of continuous loads when calculating service loads it states each of the different loads to be used when performing the service calculations.

I see 220.14(C) tells you to use 430.22 for motor outlets which in turn says to use 125% of the motor load.

Obviously the 125% is part of branch circuits article 210.20.

Third -

Why is 220.18 (B) even in there. If I calculated my load for lighting based on 220.12 what is the point in mentioning this about LED lighting?

Thanks for looking.
 
220.12 is addressing the total lighting load of all the branch circuits. 220.18 is addressing the individual branch circuits. So if we had a 1000 ft² barber shop, 220.12 requires you to allow for 3 kVA of lighting load in the service calc. You could light it up with two 20A branch circuits. Imagine we are using 20 LED lights with 150W lamps and 200W drivers. If we calculate the load on our two circuits with the lamp load it's only 1500W each. But 220.18(B) says "Look at the drivers!" Now we have 4 kW of lighting load and two circuits aren't enough anymore.

(This example is not approved by any sane lighting designer or authority having jurisdiction over the Energy Code.)
 
LibertyEngineering said:
Part II of article 220 says nothing about needing to use 125% of continuous loads when calculating service loads it states each of the different loads to be used when performing the service calculations.

I see 220.14(C) tells you to use 430.22 for motor outlets which in turn says to use 125% of the motor load.

Obviously the 125% is part of branch circuits article 210.20.
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The 125% for "continuous loads" has nothing to do with load calculations.
 
JoeStillman said:
220.12 is addressing the total lighting load of all the branch circuits. 220.18 is addressing the individual branch circuits. So if we had a 1000 ft² barber shop, 220.12 requires you to allow for 3 kVA of lighting load in the service calc. You could light it up with two 20A branch circuits. Imagine we are using 20 LED lights with 150W lamps and 200W drivers. If we calculate the load on our two circuits with the lamp load it's only 1500W each. But 220.18(B) says "Look at the drivers!" Now we have 4 kW of lighting load and two circuits aren't enough anymore.

(This example is not approved by any sane lighting designer or authority having jurisdiction over the Energy Code.)
Click to expand...
I see said the blind man as he picked up his hammer and saw.... Also I missed 220.10 which does not include 220.18. Need to stop doing this late at night but its the only time I have to peacefully look at the Code. Thank You!
 
david luchini said:
See 220.60
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Thank You! Exactly what I was looking for. IMO that should be in Part II since it says to use part II to determine the rating of the service disconnect. I am sure there is a round about way it is included in Part II by way of reference somewhere, NFPA is famous for doing that.
 
david luchini said:
The 125% for "continuous loads" has nothing to do with load calculations.
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I agree except for with Motor Outlets 220.14 (C). This tells you to use 430.22 & 430.24 which both indicate 125% of the rated load of the motor with 430.24 being 125% of the largest motor. Thanks!
 
david luchini said:
The 125% for "continuous loads" has nothing to do with load calculations.
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But after you do a load calculation, you typically need to know what fraction of the resulting load is continuous, right?

So you either have to track the continuous portion of the inputs into the computation and track that through the computation, or perhaps repeat the computation looking only at continuous loads. Sometimes it's not clear how exactly to do that, as different methods could give different answers for what portion of the total load is continuous.

Cheers, Wayne
 
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