# Church load calculation.



## FranklinsApprentice (Apr 15, 2012)

Please forgive my ignorance, it's been a while since ive been in trade school,

I have to do a load calculation for a church. The utility says the service is too large for there transformer and I need to determine what the calculation is too size there transformers appropriately.

In Article 220 I see that it's 1 va/ sq ft but does that pertain to the whole building. Theres the sanctuary and then theres an office wing, and there's a fellowship hall where they have large meals and receptions. 

Also it's a 208/120 3 phase system and only a few of the larger ACs are 3 phase, the rest are 2. Because of nameplates I could only get HP on some ACs and Amps on others. I remember something about multiplying 1.732 when dealing with 3 phase but i can't remember how to apply it when doing a load calc.

And finally, there are maybe a 100 or so 500 watt light fixtures lighting the sanctuary. Do I add those into the load calc or are those included in the general lighting. 

I'm sure I didn't give all the info necessary so please ask me what else you would need or point me in the right direction in the code.

Thank you so much.


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## BBQ (Nov 16, 2010)

FranklinsApprentice said:


> Also it's a 208/120 3 phase system and only a few of the larger ACs are 3 phase, the rest are 2. Because of nameplates I could only get HP on some ACs and Amps on others. I remember something about multiplying 1.732 when dealing with 3 phase but i can't remember how to apply it when doing a load calc.


You need to convert the AC loads to VA.

I would treat the office area as office and the church area as church.


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## FranklinsApprentice (Apr 15, 2012)

BBQ said:


> You need to convert the AC loads to VA.
> 
> I would treat the office area as office and the church area as church.


Are the 3 phase ACs 208 x amps x 1.732?

And what about the 500 watt light fixtures?


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## Cletis (Aug 20, 2010)

*VA*

Just get your total VA, multiply by any demand factors and divide by 208(1.73) or 360


So, 100,000 watts / 360 = 277.777778 amp service min


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## Cletis (Aug 20, 2010)

*Or this*

STEP 1 Use Table 220.3(A) (2005-220.12) and multiply lighting load va to total square footage. Feeder conductor at 125% for continuous load.

STEP 2 Demand load for motel, hospital, warehouse. (Table 220.11) (2005-220.42) All others at 100%.

STEP 3 Compare heat with A/C. Omit smaller. (220.21) (2005-220.60)

STEP 4 Heavy-duty lampholders at 600va each. (220.3(B)(5)) (2005-220.14(E)) 
Other outlets at 180va each. (220.3(B)(11)) (2005-220.14(I))
Multioutlet assemblies each 5-foot at 180va each. (220.3(B)(8)) (2005-220.14(H))
Show window lighting each linear foot at 200va each. (220.3(B)(7) (2005-220.14(G))

STEP 5 Demand for receptacle loads over 10kva. (220.13) (2005-220.44)

STEP 6 Demand for kitchen equipment. (Table 220.20) (2005-220.56)

STEP 7 Largest motor increased by 25%. (220.14) (2005-220.50)

STEP 8 Size the service by dividing the total va by the applied voltage. Use Table 250.66 to size grounding conductor. (It cannot be smaller than the neutral)


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## erics37 (May 7, 2009)

God will supply the lighting so you can leave that out of your calculation.


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## Cletis (Aug 20, 2010)

*day*

That's daylight harvesting


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## erics37 (May 7, 2009)

Cletis said:


> That's daylight harvesting


And soul harvesting :blink:


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## Cletis (Aug 20, 2010)

*heat strips*

better add 20k for heat strips kicking in when this happens too


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## dronai (Apr 11, 2011)

Hire a professional !


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## 10492 (Jan 4, 2010)

FranklinsApprentice said:


> I have to do a load calculation for a church. The utility says the service is too large for there transformer and I need to determine what the calculation is too size there transformers appropriately.


It is not your job to size a utility transformer. They can pull records and see the church's load, historically, and size their own equipment.

FWIW


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## FranklinsApprentice (Apr 15, 2012)

Dnkldorf said:


> It is not your job to size a utility transformer. They can pull records and see the church's load, historically, and size their own equipment.
> 
> FWIW


And they did. The engineer called me and told me they need a load calculation submitted with a application. The utility engineer told me they have a 150 Kw transformer but are running in the 200-300's most months.


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## FranklinsApprentice (Apr 15, 2012)

OK, so I did the load calc. The total came out to 415 kva. I can't believe the 150 kva transformer has held up. Somebody really dropped the ball on this one. I got the original prints from 2004 and they increased the service from 400 to 1200 but never requested the transformer to be upgraded. The ACs alone are 300 kva


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## user4818 (Jan 15, 2009)

FranklinsApprentice said:


> I can't believe the 150 kva transformer has held up.


It's not that hard to believe considering that utilities will factor the true load on their equipment and system to be 50% or less of the NEC calculations. They have historical load data to back their assumptions.


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## FranklinsApprentice (Apr 15, 2012)

Peter D said:


> It's not that hard to believe considering that utilities will factor the true load on their equipment and system to be 50% or less of the NEC calculations. They have historical load data to back their assumptions.


But does that make sense why the voltage drops to 106-108, and the sound system goes awry?


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## user4818 (Jan 15, 2009)

FranklinsApprentice said:


> But does that make sense why the voltage drops to 106-108, and the sound system goes awry?


That makes sense, but utility transformers are rated and designed to operate well past their ratings. Nevertheless, clearly the one in your situation is too small.


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## CADPoint (Jul 5, 2007)

Which problem are you there to fix ?


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## FranklinsApprentice (Apr 15, 2012)

CADPoint said:


> Which problem are you there to fix ?


Originally the sound system. Snap crackling and popping when the ACs turned on. The more ACs turning on the worse it got.


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## 10492 (Jan 4, 2010)

FranklinsApprentice said:


> OK, so I did the load calc. The total came out to 415 kva. I can't believe the 150 kva transformer has held up. Somebody really dropped the ball on this one. I got the original prints from 2004 and they increased the service from 400 to 1200 but never requested the transformer to be upgraded. The ACs alone are 300 kva



I bet it's a case of the POCO knowing about it, and using "deferred maintenance" as the excuse. 

Was there a severe voltage drop present?

I doubt this has anything to do with A/C noise in a sound system though.....


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## FranklinsApprentice (Apr 15, 2012)

Dnkldorf said:


> I bet it's a case of the POCO knowing about it, and using "deferred maintenance" as the excuse.
> 
> Was there a severe voltage drop present?
> 
> I doubt this has anything to do with A/C noise in a sound system though.....


There is a severe voltage drop. When the AC's kick on, the voltage drops to 106-108 volts on the sound system. I don't think the ACs are directly affecting the sound system, just the sound system not liking the fact that its not getting 120 volts


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