Existing Load Calculation with Utility Bill

[Electricalhelp]

I was able to get a years worth of Utility Bill from the owner.
The existing incoming electrical service is 1000A/208V/3P.

After reviewing all the bills the highest kWh and kW was
Use: 47,200 kWh
Total kW billing demand: 137.60 kW
The bill also gives me a load factor of 46%.

Based on reading the pervious post, kWh does not help with determining the existing load .

If I use a power factor of 80%, I get (137kW)/.8 = 171.25kVA / √3*208 = 476A.

But I was wondering if I have to take the Total kW billing demand and divide it by 30 days, since the billing period was for 1 whole month.

I was wondering if my calculation was correct if I was using section 220.87 in the NEC too

 

[David Castor]

What are you trying to determine? The demand is the highest power usage averaged over a fixed time (15 min, 30 min or 60 min, usually). This represents the peak load. It's a power measurement in kW. You are interested in the maximum demand during the year. Dividing it by 30 days, doesn't really tell you anything. This maximum demand is what is referred in 220.87.

The load factor of 46% means that the AVERAGE power usage was 46% of the maximum demand, based on the kWH and the number of hours in the billing cycle. But generally, the system has to be designed for the maximum.

Does the bill give the power factor or kVA used? 0.8 is pretty conservative, so it should be safe.

 

[petersonra]

I was able to get a years worth of Utility Bill from the owner.
The existing incoming electrical service is 1000A/208V/3P.

After reviewing all the bills the highest kWh and kW was
Use: 47,200 kWh
Total kW billing demand: 137.60 kW
The bill also gives me a load factor of 46%.

Based on reading the pervious post, kWh does not help with determining the existing load .

If I use a power factor of 80%, I get (137kW)/.8 = 171.25kVA / √3*208 = 476A.

But I was wondering if I have to take the Total kW billing demand and divide it by 30 days, since the billing period was for 1 whole month.

I was wondering if my calculation was correct if I was using section 220.87 in the NEC too

You cannot use an average. It is the maximum load. IIRC, usually this is expressed as the maximum load for 15 minutes during the year.

There are a couple other things that using this approach requires that people tend to gloss over. Take a look at 220.87 (2) and (3).

 

[Electricalhelp]

What are you trying to determine? The demand is the highest power usage averaged over a fixed time (15 min, 30 min or 60 min, usually). This represents the peak load. It's a power measurement in kW. You are interested in the maximum demand during the year. Dividing it by 30 days, doesn't really tell you anything. This maximum demand is what is referred in 220.87.

The load factor of 46% means that the AVERAGE power usage was 46% of the maximum demand, based on the kWH and the number of hours in the billing cycle. But generally, the system has to be designed for the maximum.

Does the bill give the power factor or kVA used? 0.8 is pretty conservative, so it should be safe.

Trying to determine if the existing service can accommodate 2 new Rooftop units. I need about 100 AMP/208V/3P

So the maximum demand is the highest load consumed (kW) in one month throughout the year period. So my estimate for the maximum demand is correct at 476A.

You cannot use an average. It is the maximum load. IIRC, usually this is expressed as the maximum load for 15 minutes during the year.

There are a couple other things that using this approach requires that people tend to gloss over. Take a look at 220.87 (2) and (3).

Thanks for help at Section 220.87(2). I would have missed it.
476A * 1.25 = 595A so 600A.
So if I add the new 100A, I am looking at 700A.
I used 80% factor just to be safe.