How much clearing for a PCB?

[Nocturna81]

So I was wondering the following: what is the minimal safe distance for a trough hole pcb to be mounted on a metal enclosure? The pcb will have 12V running through it with at most 2.5A so nothing too exciting.

Hope anyone can answer this one!

 

[nenad88]

Standard hex standoff size.

 

[Nisbeth]

Not sure there is a standard for 12V? For 230VAC mains the clearance requirement is 6mm IIRC.

 

[Nocturna81]

Standard hex standoff size.

Ehr, which would be? I have them as small as 5mm

 

[OlegSh]

I typically use 8 or 10 mm long hex standoffs depending on how tight I want it to be. You just have to make sure that long protruding component leads do not come too close to the enclosure bottom even if the PCB or the bottom cover bends due to various use or handling conditions.

Regards,
Oleg

 

[OlegSh]

With 5mm standoffs one can run into problem that standard 5~6mm long screws are too long to tighten.

 

[Nocturna81]

I typically use 8 or 10 mm long hex standoffs depending on how tight I want it to be. You just have to make sure that long protruding component leads do not come too close to the enclosure bottom even if the PCB or the bottom cover bends due to various use or handling conditions.

Regards,
Oleg

That's actually a good one, hadn't thought about that!

 

[Mark Tillotson]

Adding insulation on the inside of the case can be useful if clearance might be iffy - but not gaffa tape(!). I've used kapton tape for this in small diecast boxes.

 

[olsond3]

Heavy parts in the middle of the board and dropping it while powered on can get exciting if there isn't sufficient clearance. I just assume everything gets pulled off the table by someone tripping on the cable.

 

[MAAC0]

If You use a long screw say 20mm You can add 2 or 3 female screws to adjust the height. I usually use 3 between chassis and PCB.

 

[Nocturna81]

Adding insulation on the inside of the case can be useful if clearance might be iffy - but not gaffa tape(!). I've used kapton tape for this in small diecast boxes.

Isn't that a bit fragile? The kapton tape that is?

And wouldn't the tape start peeling off after some time?

 

[rayma]

Isn't that a bit fragile? The kapton tape that is?

Yes, instead we use Nomex 410 sheet stock, which is very tough and has a high voltage rating.
It can be cut with good scissors, punched, or die cut. We punch it to clear the spacers and install it
between pcbs and the chassis. No need for adhesives, since it is captive.

 

[fredbloggstwo]

I also use FR4 copper-clad board with the copper side down: use plastic spacers between it and the PCB above and between it and the chassis. The copper side can also double up as a ground screen for audio work.

Mike