Question on kw reading on Poco bill

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KWH

Senior Member
I was going to use the Poco bills for the last year to show loads on an existing building that is having an addition put on, my question is with the kw for the month do you divide by voltage alone or x 1.73. This is 3 phase
 
charlie b

charlie b

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Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
The utility bills generally do not show the maximum demand experienced during the month, in units of KW, but rather the total energy used, in units of KW-Hr. That would not be of use. But if the utility bills do show a maximum KW, then the steps you need to take next would be,
  1. Convert KW to KVA, by assigning an appropriate power factor.
  2. Add 25%, as required by 220.87.
  3. To convert to amps, you divide by the line-to-line voltage, and then divide again by the square root of 3.
 
Besoeker

Besoeker

Senior Member
Location
UK
KWH said:
I was going to use the Poco bills for the last year to show loads on an existing building that is having an addition put on, my question is with the kw for the month do you divide by voltage alone or x 1.73. This is 3 phase
Click to expand...
I assume you mean current and kWh?
You can't determine current from kWh alone.
Do all three phases take equal currents?
Do they all have the same power factor?

If the answer to either is no, you can't calculate the currents.
 
kwired

kwired

Electron manager
Location
NE Nebraska
KWH said:
I was going to use the Poco bills for the last year to show loads on an existing building that is having an addition put on, my question is with the kw for the month do you divide by voltage alone or x 1.73. This is 3 phase
Click to expand...

Like Charlie said - if they don't give you a maximum demand then the total kWhr is fairly useless. How do you know whether or not the usage was evenly spread out throughout the month or if it was mostly accumulated during a certain time period?

If you are trying to figure out service or feeder related information you need to be able to carry the maximum demand and not necessarily the average for the whole month.
 
Jraef

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
It's surprising to me how much this question comes up. I'm not sure if it has in here before, but I get that all the time when people are trying to determine things like bus sizing or demand. I have had one guy even ARGUE with me, trying to tell me I was wrong on this argument:

jraef: If you have 1,000,000W for 1 hour, that's 1 MWh, right?
Noob123 (name changed to protect the innocent): Right.
jraef: But if you have 1W for 1,000,000 hours, that's still 1 MWh right?
Noob123: Right
jraef: So how can you determine the demand from a reading on the bill that just says 1MWh?
Noob123: You are reading too much into it. The peak demand in that situation is 1MW, so if the voltage was 480V 3 phase and .8pf, the peak current would be 1500A.
Click to expand...

:slaphead:
 
H

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
KWH said:
I was going to use the Poco bills for the last year to show loads on an existing building that is having an addition put on, my question is with the kw for the month do you divide by voltage alone or x 1.73. This is 3 phase
Click to expand...

What type of building? Generally commercial buildings are on a different rate than residential and use demand meters. Three phase should be a demand meter. Look at the bill again to see if demand is on there.
 
K

KWH

Senior Member
Yes, The demand is listed. I just wasn't sure on changing that number over to amps. I know the method for a service calc. but wasn't sure on a meter reading, what had me asking was their peak demand was around 450amps and the building has a 1600amp service.

Thanks
 
H

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
KWH said:
Yes, The demand is listed. I just wasn't sure on changing that number over to amps. I know the method for a service calc. but wasn't sure on a meter reading, what had me asking was their peak demand was around 450amps and the building has a 1600amp service.

Thanks
Click to expand...

I'm going to assume 450 kW and use that.
voltage and 1.73.

I cheat and use 360 for 208V system, and 830 for 277/480.
So 450000/360 or 450000/830
 
F

fmtjfw

Senior Member
Location
Fairmont, WV, USA
Demand charges are almost always based on the average for a 15 minute period. The actual instantaneous peak can be higher. To determine that you need recording ammeters or "max" setting on ammeters.
 
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