Menu 0

Sorry, Your Browser Is Not Supported

You can still browse the site but some services may not work properly. This site requires Google Chrome, Firefox, Safari or Internet Explorer 10 and above. For mobile devices use an HTML5 capable browser.

Download Chrome

Sizing Lighting Loads

One step in sizing conductors and overcurrent protection for branch circuits is to determine if the load is continuous or noncontinuous. For the typical production facility, the lighting in the production area is always on. Like most industrial and commercial lighting loads, it’s continuous.

Except for incandescent lamps, it’s usually bad to cycle lamps on and off frequently. One reason is the inrush current. Because incandescent lamps are almost purely resistive loads, their inrush current is negligible. The ballasts for metal halide, sodium fluoride, and fluorescent lamps (the most common types for industrial/commercial) have high inrush current; thus, frequent cycling is inadvisable.

With LEDs, a similar problem arises because there’s a switching power supply producing 5V or similar to drive the lamp(s). If you put a power analyzer on a receptacle that’s also powering a computer, and cycle it on and off, you’ll see why you don’t want to cycle LED lamps on and off.

Lighting controls for non-incandescent lighting schemes usually involve dimming rather than on/off. Thus, these loads are continuous whether they are on a control system or not.

What about incandescent lighting on occupancy sensors? You can examine the application and determine that the lights are never on for as long as three hours. Or, you can factor in the likelihood that the lamps will eventually change to another technology. Under this assumption, you apply the 125% rule so the feeder and overcurrent protection devices don’t have to be changed to accommodate the new technology.

Source: Mark Lamendola | Mindconnection