definition of Load Factor regarding B.310
- Thread starter badgers
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- Lockport, IL
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- Semi-Retired Electrical Engineer
I have a text book from my MS program that includes a definition of that term, but I don't have it with me at present. I know this term is not defined in the NEC. What I recall is that the term refers to "Average divided by Peak."
As an example, suppose that a factory runs at a load of 200 KVA for 12 hours a day, and shuts down completely (0 KVA load) for the other 12 hours. The average value is 100 KVA. The peak value is 200 KVA. The Load Factor is 50%.
Trouble is, most buildings are more likely to run at a Load Factor closer to 75%. So I do not know why they put a value of 50% in the table. You generally can't get there, so that column is useless.
As an example, suppose that a factory runs at a load of 200 KVA for 12 hours a day, and shuts down completely (0 KVA load) for the other 12 hours. The average value is 100 KVA. The peak value is 200 KVA. The Load Factor is 50%.
Trouble is, most buildings are more likely to run at a Load Factor closer to 75%. So I do not know why they put a value of 50% in the table. You generally can't get there, so that column is useless.
Thanks but for the medical offices we do I would bet 50% is right.
The clinics are open 7:30 to 5:00 for a lot of our clients(some even less). We don't go to zero but darn close for more then 14 hours. Boiler pumps don't draw that much and we use Terminal Air Blenders so only 1/3hp motors turn on in the exterior zones for heating in the winter. Cooling is set way back and it is getting to be night time so maybe one stage comes on.
The tablet PCs that they use today don't put off that much heat while on their chargers. These clinics have little computer switches that link them to the home data center so that little leibert cooling unit is only a ton of cooling.
I think the TP-1 study was looking at 35% 24 hour load on transformers. With the energy codes shutting off all the lights the only thing on is some parking lot lights, and some minimal coputer loads.
I think 75% would be a worst case building. Like a surgery center with the constant cooling for the re-heat systems they use. Most of the sterilizers are electric self generating steam 30KW units or a bulk 180KW unit that runs for 3 hrs a day. Huge peak but no where near a significant 24 hour average.
thanks, for your help, did you book tell you why I can't use the 90?C table for the de-rating of THWN-2 or XHHW-2 wire in the conduit?
The clinics are open 7:30 to 5:00 for a lot of our clients(some even less). We don't go to zero but darn close for more then 14 hours. Boiler pumps don't draw that much and we use Terminal Air Blenders so only 1/3hp motors turn on in the exterior zones for heating in the winter. Cooling is set way back and it is getting to be night time so maybe one stage comes on.
The tablet PCs that they use today don't put off that much heat while on their chargers. These clinics have little computer switches that link them to the home data center so that little leibert cooling unit is only a ton of cooling.
I think the TP-1 study was looking at 35% 24 hour load on transformers. With the energy codes shutting off all the lights the only thing on is some parking lot lights, and some minimal coputer loads.
I think 75% would be a worst case building. Like a surgery center with the constant cooling for the re-heat systems they use. Most of the sterilizers are electric self generating steam 30KW units or a bulk 180KW unit that runs for 3 hrs a day. Huge peak but no where near a significant 24 hour average.
thanks, for your help, did you book tell you why I can't use the 90?C table for the de-rating of THWN-2 or XHHW-2 wire in the conduit?
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
If you can justify a 50% LF, then more power to you. :roll: (No, I?ll not apologize for the low-class engineering humor. :grin: )
Na. It?s just an old college textbook, and it does not say anything about the NEC. However, the second sentence of NEC article 110.14(C) tells us that you can do exactly what you describe. Is anyone telling you that you cannot?badgers said:
The client hired an second electrical engineer to review the drawings.
I shared my calculations and I used the 90?C value in my calculations.
He said that I had to use the 75?C value for derating.
I know the lugs are 75?C but this is a calculation based on temperature in the conduit.
I have always used 90?C table when derating in a conduit based on mutual heating effects, or high ambient.
I wanted to see if there was a quick becuase it was a duct bank requiring the use of 75?C.
Its always good to double check before I put it in writing back to him.
I shared my calculations and I used the 90?C value in my calculations.
He said that I had to use the 75?C value for derating.
I know the lugs are 75?C but this is a calculation based on temperature in the conduit.
I have always used 90?C table when derating in a conduit based on mutual heating effects, or high ambient.
I wanted to see if there was a quick becuase it was a duct bank requiring the use of 75?C.
Its always good to double check before I put it in writing back to him.
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