When assisting a customer in selecting a loadcenter for an application, it is best to start by interviewing the customer to determine the application’s requirements.

Ask whether this application will involve an indoor or outdoor installation. This will determine the enclosure type for the loadcenter.

NEMA Type 1 General Purpose	This enclosure type is for general purpose, indoor use. It is suitable for most applications where unusual service conditions do not exist. It provides protection from accidental contact with enclosed equipment.
NEMA Type 3R Raintight	This enclosure type is intended for outdoor use. It provides protection against falling rain, sleet, and snow.

If it is an indoor installation, ask whether it will be flush-mounted or surface mounted.

Ask whether the loadcenter is to serve as a service entrance panel or a distribution panel.

Ask whether the application involves a single-phase, three-wire system or a three-phase, four-wire system.

Ask what type of main, either a Main Lugs Only or a Main Circuit Breaker.

Ask for the main ampere rating.

Ask what type and rating main breaker is required, if applicable.

Ask for the number of breakers required, and for their ratings.

Ask how many spaces are required. The customer may want to leave extra spaces in the loadcenter for future needs.

Once this information is obtained, go to the product catalog. These questions should cover everything needed to recommend products that fit the customer’s application needs.

To assist you in visualizing the product selection process, let’s consider a commonplace customer application.

Suppose a customer comes to you and wants to add two branch circuit breakers to an existing loadcenter for a newly remodeled kitchen. How would you go about sizing the breaker?

First, interview the customer to find out what loads will be on the branch circuits. Let’s say that one will be dedicated to a dishwasher, and the other will be dedicated to a garbage disposal.

Next, obtain the amperage requirements of the loads from the customer. Suppose the dishwasher runs on 12.5 amps and the garbage disposal runs on 9.8 amps.

Based on these numbers alone, you might think that it would be a good idea to recommend a 15 amp breaker for the dishwasher circuit, and a 10 amp breaker for the garbage disposal circuit. But this would result in a lot of nuisance tripping.

So, we need to do a little simple math. Figure in a 25% safety margin by multiplying the amp ratings by 1.25.

This will be sufficient to eliminate nuisance tripping, but the breakers will still trip in the case of a true overload condition.

Based on these calculations, you would recommend a 20 amp breaker for the dishwasher circuit, and a 15 amp breaker for the garbage disposal circuit.