Mains carrying PCB standoff height reccomendations

[negativ3]

Hey all,

I have a transformer which I have built input and output protection boards for.
Looking to mount the PCBs within the enclosure.
Are there any recommendations to guide minimum standoff height required?
240V AC @ 50Hz input, 120V AC output.
Max 2 Amps.
Component legs extend 1mm (max) beneath the PCBs.
Looks like 5mm nylon 66 standoffs I have will fit well with plenty clearance around all other components to the PCB.

Is 4mm acceptable?

Thanks
Andy

[Benta]

4 mm is fine if the distance is fixed. But it depends a lot on PCB flexing. If the assembly is stiff, go ahead.

[negativ3]

4 mm is fine if the distance is fixed. But it depends a lot on PCB flexing. If the assembly is stiff, go ahead.

Standard FR4.

Thanks.

[Gyro]

I recommend placing a thin insulating sheet between the chassis and the PCB (loosely fitted around the standoffs is fine) as additional protection against loose conductive items falling under the PCB or PCB flex if dropped. Polyester binder cover overhead, transparency material, etc. is fine.

4mm is fine for a safely and reliably grounded chassis, 3 wire mains lead, power outlet etc. If there's any doubt about this, you need to go to 8mm (reinforced insulation). but you should avoid this situation.
 

[Benta]

Let's not go over the top here. 8 mm reinforced is creepage distance, not clearance which is the case here.
But I agree on the insulation sheet, that's always good practice.

[Gyro]

I designed a bunch of mass market Class II metal cased consumer AV products in the late '90s / early 2000s. We always worked to 8mm clearance (and creepage of course). Unfortunately I no longer have access to the relevant EN60065* standard. As I said, the OP should avoid getting into such a Class II situation anyway.


Edit: * Which itself has been superseded anyway (just like me!)