Amps from Watts and Volts

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solobrac

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Location
Troy, Alabama
I feel like the answer is pretty obvious, but I am reaching out for second opinions. The Utility I work for is supplying power to a particular industrial business. The business has contacted us wanting to know the peak demand for their company over the past 12 months. I pulled the reports and I have: Demand Read, Demand Consumption, and Total Consumption. There are now units on these numbers but if I am not mistaken the Demand Read should be kW and Demand Consumption should be kw/h. First off can someone please explain these three numbers to me. Secondly, I need to know the peak amps for the company. I know that this is a 208V 3-phase but I do not have a power factor. If I remember correctly kW = (1.73*Volts*Amps*power_factor)/1000. Unfortunately I do not know the pf of the system so how am I going to be able to find amperes??
 
dkidd

dkidd

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here
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PE
Give them the peak demand in KW. Unless they specifically ask, they probably don't need amps. As you said, without power factor, amps can't be calculated.
 
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Carultch

Senior Member
Location
Massachusetts
solobrac said:
I feel like the answer is pretty obvious, but I am reaching out for second opinions. The Utility I work for is supplying power to a particular industrial business. The business has contacted us wanting to know the peak demand for their company over the past 12 months. I pulled the reports and I have: Demand Read, Demand Consumption, and Total Consumption. There are now units on these numbers but if I am not mistaken the Demand Read should be kW and Demand Consumption should be kw/h. First off can someone please explain these three numbers to me. Secondly, I need to know the peak amps for the company. I know that this is a 208V 3-phase but I do not have a power factor. If I remember correctly kW = (1.73*Volts*Amps*power_factor)/1000. Unfortunately I do not know the pf of the system so how am I going to be able to find amperes??
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Demand should be in kilowatts-"instantaneous". Understand that the kW-hr unit is kilowatts multiplied by hours, a unit of cumulative energy. Kilowatts themselves are a rate unit of power, which are energy units (Joules) per unit time (seconds).


I put "instantaneous" in quotes, because it really isn't instantaneous. It is relatively instantaneous when you compare it to a day or a month or a year. But what it really is, is a 15 minute interval average. So total energy in 15 minutes divided by the duration of 15 minutes. If you know the 15 minute total energy in kW-hrs, then you divide by 1/4 hour, which really means multiplying by 4 and dividing out the units of hours.
 
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solobrac

Member
Location
Troy, Alabama
dkidd said:
Give them the peak demand in KW. Unless they specifically ask, they probably don't need amps. As you said, without power factor, amps can't be calculated.
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The company has indeed asked for amps to see if their panel can handle adding some more load. I know it is not conventional but they are the customer and I just have to give the info they ask for.
 
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GoldDigger

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Location
Placerville, CA, USA
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Retired PV System Designer
solobrac said:
The company has indeed asked for amps to see if their panel can handle adding some more load. I know it is not conventional but they are the customer and I just have to give the info they ask for.
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Similarly to the Brazil versus Facebook case, they would be unreasonable to demand information that you do not have.
 
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Iron_Ben

Senior Member
Location
Lancaster, PA
solobrac said:
The company has indeed asked for amps to see if their panel can handle adding some more load. I know it is not conventional but they are the customer and I just have to give the info they ask for.
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All the responses you've gotten to your original post so far are very good. And as you alluded to in that post you simply cannot calculate amps without knowing the power factor. It would be foolish in my view to assume a power factor of 0.8 or some such. If we knew the nature of the customer, the type of operation it is, we might be able to hazard an educated guess but there's a lot of risk there. I've seen office buildings with the power factor as high as 0.9 and I've also seen sugar mills and rice mills as low as 0.62 or so. That's a huge disparity.

Also note that the units of energy are kwh, not kw/h. Watt hours --> energy and watts --> power. We do have one poster here who thinks that watt hours are a unit of power, but that's a story for another day.
 
mivey

mivey

Senior Member
Demand read vs demand consumption is vague but could be before and after meter multiplier. If the numbers are similar in size then that is not the case.

It could also be the monthly demand vs the billing demand. If the demand consumption stays the same a lot of the time while the demand read changes regularly then demand consumption is the billing demand (could maximum over several months with some weighting factors).
 
mivey

mivey

Senior Member
It would be up to them to find the amps. You can only provide the data you have. If you want to go above & beyond, you could offer to meter the pf during high load or to install a temporary recording meter.
 
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Carultch

Senior Member
Location
Massachusetts
Iron_Ben said:
We do have one poster here who thinks that watt hours are a unit of power, but that's a story for another day.
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I'm not seeing anyone in this particular discussion who posted a response that would indicate such a misconception. Perhaps you are referring to other discussions on this forum.
 
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Iron_Ben

Senior Member
Location
Lancaster, PA
Carultch said:
I'm not seeing anyone in this particular discussion who posted a response that would indicate such a misconception. Perhaps you are referring to other discussions on this forum.
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I am! There was a thread about 3 or 4 weeks ago where the misconception came up repeatedly. The final tally was about 15 engineers to 1 engineer that the watt hour is a unit of energy and the watt a unit of power.
 
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Ingenieur

Senior Member
Location
Earth
mivey said:
It would be up to them to find the amps. You can only provide the data you have. If you want to go above & beyond, you could offer to meter the pf during high load or to install a temporary recording meter.
Click to expand...

This^^^^
put a recording meter on the service for a few cycles of normal operation
otherwise give them the peak kw and let their engineer determine current
 
junkhound

junkhound

Senior Member
Location
Renton, WA
Occupation
EE, power electronics specialty
give them the peak kw and let their engineer determine current

hah, company probably has no one who can even operate a calculator, or they could just take the numbers off the last few billing cycles. Obvious they have no one that knows how to squeeze the handle get the jaws open on an ammeter ?

That is why they ask, someone did figure out how to read the number on a CB hancle and compare it to a NEC table?
 
junkhound

junkhound

Senior Member
Location
Renton, WA
Occupation
EE, power electronics specialty
OK, good point, amend to read......, ...and plug the ammeter into a scopemeter to record a few days worth of minute by minute readings <G>
 
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