Amps, kW, and NEC Ratings Æ the Brake Horsepower Game
Contributed by Zoeller Engineering Department
For a long time in the business of selling submersible pumps, there has been a game that
some pump manufactures play with published brake horsepower (BHp) and pump efficiency.
This game involves rating a pump with a high pump efficiency and BHp but the overall efficiency
(wire-to-water) is the same or less than the competition. This is done mathematically by placing
certain hydraulic losses into the motor losses that will cause the BHp and pump efficiency to be
higher. Since many manufactures do not list the overall efficiency or kW input in their catalog,
the typical customer will never know. The important thing is not what the BHp rating of the pump
is but how much power will it use in a certain application. Zoeller Company does not and will not
play games with our ratings. This article will try to explain some of the differences between our
ratings verses the competition.
Many people once asked us why it takes a larger BHp pump from us to do the same thing as
another manufactures smaller BHp pump. Well the answer was two fold. First, at one time our
pump efficiency was not as high as our competition, but we have done some things through
hydraulic changes to improve over the last three years. We now have fixed this problem on all
models (for models greater than 20 BHp consult the factory because the new curves are not in
the catalog).
The second part of the riddle comes from how we rate our product. The National Electric
Code (NEC) gives certain guidelines for the full load amp (FLA) requirements on electrical
equipment. We at Zoeller are trying to follow these guidelines so the electrician will provide the
correct branch circuit for the pump equipment. This is not always true for other manufactures.
Sometimes the FLA will far exceed the maximum set forth by NEC.
So the next time someone questions our pump ratings, remember, there is more to it than
just comparing the BHp ratings between two pumps, try comparing the amps / kW also. The
BHp rating is not nearly as important as how much power will the product consume.
Oversizing Impellers
Our philosophy at Zoeller Company has been to provide a pump that will be non-overloading
for the entire length of the pump curve. By doing this many models will operate fine from 10’
TDH all the way to shut off. In some instances this leaves us at a disadvantage. If a specific job
has 50’ of static lift there is no way the pump will ever operate below 50’ TDH. For cases such
as this we are willing to oversize an impeller on a motor. This will give you a smaller BHp size
that will have the full life of a larger pump at a much more economical price. We call this
oversizing the impeller. Curves on many models are now available in the engineering section of
the catalog for doing this. In the future these curves will be the standard type curve found in the
Engineered Products binders. When requesting an oversized impeller be prepared with the
static head of the application because we are still cautious and will request this information from
you before we will process the order.
Catalog Changes
Steve Doolittle and myself have discussed how we plan to present our curve data in the
future. We believe it would be better for an engineered product to show a family of curves for
each model pump. This will make the ZEP catalog more mainstream with our competition. After
this catalog change all information for each model will be grouped together (technical data,
curves, dimensional data, specifications, installation manual, and maintenance manual) by
frame size. This will prevent the user from searching through the catalog to find each piece of
literature for a specific model. Another change that should help you sell more products that will
be happening soon is standardizing our horsepower ratings with NEMA criteria (i.e. 1, 1 ½, 2, 3,
5, 7 ½, 10, 15, 20, 25, 30, 40, 50, and 60 BHp). This will help our product to have easier
understood ratings instead of odd horsepower ratings as in the past. We are shooting for
implementation sometime in the 2nd quarter of 1999.