What Is Generator Sizing?
Generator sizing is the process of determining the size of generator you will need for
your particular set of circumstances.
There is a serious industry saying that goes like this, “With generators, size does matter.”
Whether you are renting, purchasing or using a generator for emergency purposes only, it is crucially important
that you select a unit that is capable of meeting your electrical needs.
In this session we’ll make this seemingly complicated process easy to understand. In just a few short moments
generator sizing will become a breeze.
I cannot stress this enough; failure to properly size your generator needs will most likely lead to one or more of
the symptoms related to generator under sizing:
Symptoms of Generator Under Sizing
||Intermittent and unreliable
||Constant unexplained shutdowns
||Inability to handle new loads as
they attempt to come on line
||Unexplained complete system
||Shutdowns as additional loads are
||Risks to personal safety and/or
||Premature maintenance problems
||Excessive maintenance problems
||Shortened system life
What Is The Key To Generator Sizing?
They key to
generator sizing is matching the anticipated power to be used to the rated output of the generator. In
layman’s terms, that means matching your power needs to the right generator.
Here’s an extremely basic barebones example of generator sizing. Let’s say you want a portable generator to
light four rooms, each with 100-watt light bulbs. You have a total need of 400 watts.
After you factor in a overage cushion of 20 to 25%, (this is recommend to compensate for fluctuating and future
loads). Your generator size will be 500 watts. Simple enough, right? There are three points we need to consider
when sizing for a generator.
Starting Load Demands
Some devices, tools, motors and appliances require more current and power when they are
initially turned on, than when they are up and running. This is called the starting load demand. This is
especially true for motors and pumps. Once the unit is fully operational, its power consumption will drop and
revert to its running load demand. To determine the correct electrical load requirements, always use starting
watts, not running watts.
Running Load Demands
The running load demand simply put, is the sum total of all the loads that will be operating
simultaneously. You can acquire this figure a number of ways.
1). By using a Clamp on AC Digital Meter. These meters will give you an accurate measurement
of your running load demands.
2). By using or Generator Sizing
Worksheet. This method will give you an approximate measurement of your running load
3). Hire an licensed electrician. This method will also provide you with an accurate
measurement of your running load demands.
Most homes are designed to operate on a dual feed, commonly referred to as: 120/240 volt service. This dual feed
service makes it possible to operate 120 volt appliances simultaneously along with 240 volt devices such as central
air conditioning units, heat pumps, clothes dryers, kitchen ranges, water heaters and well pumps. If you ever
expect to power 240 volt devices, you must select a generator with a dual 120 and 240 output.