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UL Standards: Board to Board Stack: Live/Neutral. Best Option?
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advancednewbie:
Hi all,

I'm looking for a bit of help in regards to UL standards for North America.

I have a design that involves two PCBs stacked by some standoffs. One PCB does power switching (Light dimming @ 120VAC) and the other is a power supply. The PCB for the dimming circuit is where mains is connected, but I would like to have a pin header to pass live and neutral down to the power supply PCB (which requires little input current). The spacing between boards is roughly 14.5 mm. This design will need to be certified in the future.

Can I use a regular pin header? What is the minimum pitch? I'd like to be able to take the boards apart during manufacturing and don't really want to have boards with wires soldered between them.

Thanks for your help.
ajb:
A quick look at Mouser shows mezzanine connectors with ratings up to 1.5kV, and some at least have UL listings.  A standard 100mil pin header won't give you adequate clearance or creepage unless you can remove several of the pins between line and neutral. 

I've seen a commercial product that uses a carrier PCB with bolt-on PCB modules for optional functions that actually used the standoffs themselves (insulated with heatshrink) to carry 120VAC.  I'm not sure if that product carried any UL approvals, but it certainly wouldn't be my favored approach.

What about a flying lead?  JST VH connectors (and similar 3.5-4mm pitch connectors) are commonly used on power supplies, usually 3-pin connectors with the center pin removed for line+neutral.
T3sl4co1l:
Board-to-board headers are available in wide pitch, or you can use e.g. 0.1" headers while skipping a bunch of NC pins to get clearances.  Or at worst, use separate headers, one for each connection.

You will want to check the UL recognition of the parts you choose, of course.  If they don't say enough voltage, just keep shopping!

Tim
Larry80:
There are myriad of connectors available. Minimum pitch is whatever can survive the required maximum testing voltage (this is called functional insulation). If the user does not get to unplug the thing, it is essentially a static connection just as PCB route would be?

I think 100th normal SIL header can survive many kilovolts easily between heads, the problematic part is at the soldering, where you need to route between pads and even then 1mm clearance is hard to come by (which is under the clearance limits by book). This can of course be mitigated with ie. silicone on the problematic area (UL listed of course..:) ).
Jester:
Use 200mil pin spacing and oval the pads. No pad between. Maintain adequate creepage and clearance to everything else.
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