In our last Tech Talk, we covered how to cut your fixture and install snap connectors. This week, we’re going to discuss the difference between Class 2 and Class II power supplies!
It can be difficult to specify a power supply for your project. It’s especially difficult when you’re specifying between Class 2 and Class II. The difference is a lot larger than their names imply! Rather than referring to the capabilities of the power supplies themselves, the Class 2 and Class II designations refer to the safety features in place to prevent electrical shock and fire initiation.
Class 2 Power Supplies
Class 2 defines the portion of the wiring system between the load side of a Class 2 Power Supply (beginning from the outside of a cabinet or machine) and the connected equipment. (source)
To be considered a Class 2, a power supply must meet the wiring requirements; gauge, insulation, derating factors. The NEC takes into consideration the gauge of the wire best suited for the job. Even though you could get away with using a smaller gauge wire, they require a larger gauge just to be safe. The power supply must also meet the NEC regulation requirements for over current protection; an internal safety feature that will shut the supply down or sink it to ground if it begins to draw too much current (such as during a short). They also specify the methods of wiring and installation during production of the power supply.
Class 2 circuits with a 24V output should not have loads that draw more than 100VA. If you overload the power supply, it will cause brown-outs on your fixtures. Because of this, the draw of the load limits your max run length. With lower draw fixtures, such as Vivid Contour, this is not an issue, but it can limit the max run lengths of larger draw fixtures such as Vivid S.
Because of the limitations, Class 2 Power supplies are suited for shorter run lengths and lower draw fixtures.
Class II is sometimes known as “double insulated”. This is an IEC protection class and refers to the power supply’s internal construction and electrical insulation. These regulations are in place to protect the user from electrical shock.
These power supplies are manufactured with either two layers of insulation or one reinforced layer between the user and the current carrying wires. The Class II power supply will have a two-wire power cord rather than the three-wire with the ground wire for protection. You will likely find these power supplies in a plastic casing. This is due to the requirement of grounding power supplies in metal casings.
You can identify Class II power supplies by this symbol:
Generally speaking, Class 2 designations refer to the voltage capabilities of a power supply, while the Class II designations refer to the insulation.
If you would like to read more on these classifications, check out this post on class 1, 2, and 3 circuits, and this post on the difference between the classes.