UL procedure of PCB Design

Question

I Need to design a Energy meter ( Single phase 240 Vac, 0.4 mA ) , its a industrial product with enclosure of IP 67. I need to design PCB for this product as per UL. I am new to UL procedure so please guide me.

Note 1) First Schematics and select all component, those are only UL Certified ?? what if some component are not UL listed, like resistor , capacitor , transistor,IC etc. will this PCB fail to get UL certificate.

Note 2) In Layout follow the Clearance and creepage distance.

Note 3) Find the PCB vendor who make UL rated PCB,Send the PCB for manufacturing Will PCB vendor will mark UL logo now on PCB or first PCB need to send UL lab to test and validate then in second interation we can ask PCB vendor to mark UL logo on it?

Note 4) If we need to send PCB for UL lab for certifiaction, Do we need to send bare board or assemble board or Full working unit.

Note 5) What Test lab people will run , Do I have to tell them what test need to run or do they run as per their process.

Note 6) What Standard need to follow to get UL rated PCB.

Note 7) How much designer involvement in getting UL rated PCB, should has to guide the PCB vendor for what material need to use or process.

Answer 1

While I'm by no means a UL expert, I can say this:

1) You don't need to use UL listed components to have a UL listed design, UL listing is something you get by having a finished product that passes the appropriate UL tests.

2) Yes definitely follow the appropriate creepage and clearance distances for the voltages your product is likely to encounter (using bigger clearances won't hurt at all and if you can't accommodate the clearance for any reason, board cutouts or conformal coatings can often work just as well - speak to your local UL lab)

3) I don't think there's anything special about PCBs that go into UL products other than using the right clearances and creepages (and getting a conformal coat if there's any possibility of moisture ingress)

4) the UL lab will want a finished (working) product, unless you want to get each section individually certified (which is not worth it for a product that will only be used in it's finished state). Sending them a bare board won't get you anywhere.

5) They will require at least some information on how your product will be used and what it does and the environments it will have to work in, they can most likely advise you on which tests are applicable, they won't just take your money and do some arbitrary test, they are a safety agency, if you ask for advise they have a duty to give you assistance (even if you haven't paid them yet)

6) Speak to your local UL lab, they should (and likely will) be able to give you advice on things like relevant requirements, things to avoid, that sort of thing, they have knowledge and they will likely be happy to share it.

7) Unless there is a specific need to use nonstandard materials in your PCB, I don't see much of a need to have much interaction with the PCB manufacturer, good ol' FR4 is found in thousands of UL parts (laptops, chargers, phones are almost always UL listed). The only time I'd imagine you'd need to speak to the PCB manufacturer is if you need cutout slots or conformal coating (and they can probably work out the cutouts from the cutout lines your PCB outline drawing anyway)

Answer 2

Tom gave you most of the answer, but I will add a bit (and disagree a bit) with what he wrote:

First Schematics and select all component, those are only UL Certified ??

Using UL listed parts wherever line voltage is present will significantly reduce the cost of certification. If you don't use listed parts, they will have to do the same investigation of the parts you use as they would have done to list the parts if the manufacturer had requested it. And, of course, if the manufacturer didn't design the parts to pass safety requirements, there's a good chance the parts won't pass, delaying your project.

Will PCB vendor will mark UL logo now on PCB or first PCB need to send UL lab to test and validate then in second interation we can ask PCB vendor to mark UL logo on it?

Generally, PCB vendors will have UL approval for certain laminate materials and layer counts. They will be able mark the board if you choose one of the stack-ups that they have approved. If you need to use an exotic material (maybe a low-loss rf material, or something) then they might not have approval for that and you or they would need to pursue that before the boards could be marked.

UL does not just test the creepage and clearance distance. For example, they also check the flammability of the PCB material (This is called 94 V rating).

Will PCB vendor will mark UL logo now on PCB or first PCB need to send UL lab to test and validate then in second interation we can ask PCB vendor to mark UL logo on it?

It mainly depends which market you sell your product to. For example, there are different requirements for industrial products vs. consumer products.