Emergency systems

[WA_Sparky]

Question regarding Electrical Emergency Generator sizing.

I have a 600A service, existing peak demand 115A @208V 3Ø
Theres an existing 80KW generator (Max 278A @208V 3Ø output with .8 power factor).
My new added loads plus existing peak is 350A. Typically i would just size the generator to be above demand, but i dont want to force the client to pay an additional $70K if the existing may support the load of real world demand. Is there a code requirement that requires you to size based on demand or how would one go about stating the existing gen set very well could support the loads after construction without requiring a oversizing the generator?

Thanks,

 

[texie]

Question regarding Electrical Emergency Generator sizing.

I have a 600A service, existing peak demand 115A @208V 3Ø
Theres an existing 80KW generator (Max 278A @208V 3Ø output with .8 power factor).
My new added loads plus existing peak is 350A. Typically i would just size the generator to be above demand, but i dont want to force the client to pay an additional $70K if the existing may support the load of real world demand. Is there a code requirement that requires you to size based on demand or how would one go about stating the existing gen set very well could support the loads after construction without requiring a oversizing the generator?

Thanks,

Since there are so many differences in gensets of a given size between brands and the nature of the type of load, I would go to the manufacturer to model the load for the exact genset. All the major brands have software to do this.

 

[WA_Sparky]

Since there are so many differences in gensets of a given size between brands and the nature of the type of load, I would go to the manufacturer to model the load for the exact genset. All the major brands have software to do this.

I have the name plate info and everything from the manufacturer. The issue is whether its standard practice or code required to oversize the generator to match the estimated demand calcs or if there's an alternate way of assessing the true loads with the gen max output. Similar but on a different note, a local utility engineer mentioned its common for a buildings actual demand to be roughly 40-60% of what my demand calcs show.

 

[electrofelon]

A generator with an ATS must be able to supply the load. 220.87 is a great way to size generators as it will allow actual realistic sizing without spending money for nothing which would typically happen if you used the bloated, worthless, unrealistic NEC load calcs.

I am a bit confused on your use of the word "demand" and whether you are talking about monitored demand/utility data or calculated load.

 

[WA_Sparky]

A generator with an ATS must be able to supply the load. 220.87 is a great way to size generators as it will allow actual realistic sizing without spending money for nothing which would typically happen if you used the bloated, worthless, unrealistic NEC load calcs.

I am a bit confused on your use of the word "demand" and whether you are talking about monitored demand/utility data or calculated load.

Thank you for that!

To clear up my bad terminology:
"Demand Calcs" - Calculated loads by applying demand factors to connected loads per NEC.
"Actual Demand" - Peak Demand data metered by utility