I'm trying to understand data sheets for flexible LED light strips. I'm looking at https://www.inspiredled.com/wp-content/uploads/2018/03/12V-SB-White-Flex-Spec-2.2.pdf, for example. It says:

To be installed in accordance with NEC, using Class 2 12V power supply only!

At the bottom of the subsequent table, it says:

Power Source Max Length
150W Transformer 1046.5” (135W)


Is a class 2 power supply limited to 100VA?

I've mostly dealt with DC, so I've forgotten a lot about VAs, but I'm roughly equating VA to Watt. Have I forgotten something important?

Wouldn't a 150W transformer power source violate the limits of Class 2?

Do strips like this do their own rectification so that they can be powered directly from a transformer?

Is using a switch-mode power supply rated 12V ⎓ 10A Class 2? Is it more efficient than a transformer?

Does a Class 2 power supply require a UL or other NRTL symbol to be used in the US?


1 Answer 1


Here's a piece of the puzzle... from http://escventura.com/manuals/sola_introNECclass2_rg.pdf

enter image description here

This table, "Table 11(b)", is for DC power supplies. Table 11(a) has the requirements for AC transformers.

From that same tech note, "Not inherently limited" means...

an additional protection device (usually a mechanical circuit breaker or fuse) protects against overload within a defined time. The additional protection device must be installed within or closely connected to the power source, so that it can be regarded as one unit.

and "inherently limited" means:

that the power source itself limits the output current (e.g.: using a electronic or magnetic circuitry).

It would seem that the limits on the "Not inherently limited" kind refer to the power supply + additional protection device operating together.

  • \$\begingroup\$ Great, thanks for the reference. Data from a vendor like this seems much more reliable than most web sources. \$\endgroup\$ Jun 15, 2021 at 14:43

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.