UL Testing

[craigfoo]

I'm designing a circuit for a client and he wants to send it out for UL testing. Is anyone familiar with how that process works? Do I need to follow strict UL guidelines or are the IPC guidelines good enough?

[qno]

What is it?

[craigfoo]

Circuit that measures capacitance and gives feedback whether or not the cap is out of spec. The circuit knows what the cap value and tolerance should be.

[dumpystig]

But in your other thread it seems you don't even have a circuit idea let alone a completed project???   

[craigfoo]

Not yet. I would hate to finish a design, send it to UL and get rejected. I'm just wondering if I would need to design to their standards for whatever category this project falls under. Seems to me that would be the best method.

[AndyC_772]

You need to design to UL standards, which are in many cases similar to equivalent IEC international standards. You'll save on a lot of testing if you design in parts which are already UL Recognised Components (reversed "UR" mark), or which are already UL listed.

As well as creepage and clearance distances, they're also keen on flammability. You'll need to demonstrate that any potentially combustible parts have passed a flammability test; look for a UL 94V-0 classification on any connectors, wire insulation, or other physically large plastic items.

[craigfoo]

Thanks AndyC! That's good information!

[KJDS]

You'll also need to get the board manufactured by a company with UL94V-0 approval and ensure that they label it as such.

[AndyC_772]

Another thing they're quite keen on is power supplies, and their ability to start a fire (or not). They'll want to demonstrate that the amount of power available from any power outlet is inherently limited, and although there are various techniques to achieve this, a (UL recognised) PTC fuse in series with any power supply can be a straightforward way to achieve compliance.

It's worth having a talk with a UL representative. When a product is granted a UL mark, it brings with it a level of insurance cover; UL are declaring that they believe your product to be safe, and they agree to underwrite the cost of a successful claim against you in the event that your product causes harm. Being an insurance company, they'll want to ensure that the product you're actually making is identical to the one they tested, so they carry out regular factory inspections and may ask for other documentary proof that the parts being used are the same.

It's quite an overhead, and can be a very costly process - but that's one reason why it's nice to be doing the development work, which is a one-off process, rather than being responsible for the ongoing compliance overheads once a product is in production.

[qno]

How do you want to test the capacitor?
If you use a UL certified power supply to power your setup you have no problem.