Diesel Generator Sizing for Pumps

First, please turn off the all-caps key.

The generator must be able to handle the current of whatever loads are already running, plus about three times the FLC of the motor(s) to be DOL started, or about twice the FLC if Y-Δ started. There may be some variation from mfr to mfr.

Why is it three times and not six times of FLC for DOL starting ? The starting kick is generally six times and for energy efficient motors it may be as high as seven times of FLC.

Because even though the genset is rated at so many amps, it can produce brief surges above that. There are also some complications involving rotational inertia of the generator and other motors.

Although starting current is high(6times),pf is very low during starting. Because power=1.732VI(pf) and there will be a voltage drop during starting ,starting power won't be 6 times motor rating.

Here,

http://webcache.googleusercontent.com/search?rlz=1T4ADRA_enSA483SA483&q=cache:IH9XXXMpTv4J:http://www.eaton.com/Electrical/USA/ProductsandServices/Residential/GeneratorsTransferSwitches/ProductLiterature/idcplg%3FIdcService%3DGET_FILE%26RevisionSelectionMethod%3DLatestReleased%26Rendition%3DPrimary%26dDocName%3DTD00405018E%2BTechnical+Data+TD00405018E&gs_upl=0l0l0l447lllllllllll0&safe=active&hl=ar&ct=clnk

Learning how to find knowledge outweighs knowledge itself.

First, please turn off the CAPS locks....you're essentially yelling at us!

Many genset manufacturers provide an example how to calculate the electrical load and hence size the generator/engine combo. These can be found in their engineering catalogs and sometimes on their website. Fairly easy to do, even if your not an EE. I always have a licensed EE check my work prior to letting out the project for Bid, just for QA/QC purposes. BTW, I'm a Civil Engineer, not an EE. I usually have to do this for emergency standby power functionality at pump stations of all types, water and wastewater treatment plants.

When all else fails, read the instructions first followed by a call to the genset manufacturer's tech rep.