zen
Hi Guys,
Do anyone of you uses the customer peak  in the past year from hydro to size a generator?
Have a nice day and play safe.
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78buckshot
We don't.
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zen
Why not if I may ask? Or at least have you ever compare?
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Skip Douglas SkipD
zen wrote:
Why not if I may ask? Or at least have you ever compare?
There are very specific rules outlined in the NE (National Electrical Code) for performing generator sizing calculations.  Using any alternate methods will accomplish little more than  extracting cash from one's wallet needlessly.
Skip Douglas
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78buckshot
I'm not on the design and sales end of our company, our project managers use the calc. charts and experience.
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DanS26
No sales guy was ever fired for over-sizing a generator......but if he under sized it there will be he** to pay.
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UPS
DanS26 wrote:
No sales guy was ever fired for over-sizing a generator......but if he under sized it there will be he** to pay.


If undersized, and it does get by the inspector, the first time the owner has problems there will be....
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Brian Baughman
Using the peak kW demand over 12 months of billing history and multiplying by the required 125% is fine for light commercial applications, but most utility providers do not capture the peak kW demand on a residence.  Peak kW demand and kWh are not the same, and kWh cannot be used for any sizing calculations.  The best and most wildly accepted method is to calculate the load on the generator in accordance with Article 220 in the NEC.
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Wireform
Using the peak kW demand over 12 months of billing history and multiplying by the required 125% is fine for light commercial applications, but most utility providers do not capture the peak kW demand on a residence.  Peak kW demand and kWh are not the same, and kWh cannot be used for any sizing calculations.  The best and most wildly accepted method is to calculate the load on the generator in accordance with Article 220 in the NEC.
can you explain what article 220 is please, thanks. 
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Geoff Z
National Electrical Code (NEC) article 220 is an entire section of the code book devoted to sizing calculations for branch circuits, feeders, services, and yes generators...
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Brian Baughman
Yes, what Geoff said.  Article 220 contains all of the math formulas required to perform a sizing calculation.  Typically the responsibility will fall on the electrical contractor to perform the calculation, however some Generac dealers will have a "salesperson" perform the calculation through the Power Play Sales app.  The app has a sizing worksheet that is based on the requirements of Part III and Part IV of NEC Article 220.
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Geoff Z
You will also see the NEC called NFPA 70 (National Fire Protection Association). It is part of a much larger group of codes and standards produced by NFPA. Kind of ironic it is call National Electrical Code as it is typically adopted by individual States and Municipalities in their own time frames. It is simply the bench mark that is widely accepted. Like here in Michigan we have Part 8 rules. It indirectly adopts the NEC with deletions, additions and amendments. We also have the Michigan Residential Code (MRC) which does include electrical. So we have all 3 to consider when designing or sizing anything. A lot that goes into installing anything properly and to code.  
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