Electronics > Projects, Designs, and Technical Stuff

Isolation in AC lines on PCB

(1/3) > >>

ChrisGreece52:
Hello i am laying out a pcb and i have a question about proper isolation between the traces. Below i attached a screenshot of my current layout.
The distances i measured (from top to bottom) are : 4.856 mm and 5 mm. I live in Europe so i am working with 220V.
J1 is the input connector (L and N) , XF1 a 200 mA fuse , XF3 a thermal fuse , V1 a MOV.
K1 and K2 are 2 relays i will be using. On top the AC1 module is an AC-DC converter. (HKL-20M05)
The thickness of the traces is 1.5mm but the current draw of my circuit will 1.5 A max with a typical 800-1000 mA consumption.
My questions :
~Will there be a problem with the trace on the bottom (N) going in parallel with the one that goes to the relays (L)?
~Is the distance between L and N sufficient ?
any suggestion would be greatly appreciated since this is my first time designing a mains board.

Thank you so much.

TimNJ:
This depends on some environmental characteristics like expected surface contamination, comparative tracking index (CTI) of the PCB material, altitude, etc.

For sealed medical power supplies, indoor use, the requirements for line-to-neutral spacing is 2.96mm, for altitudes up to 5000m. If you're measuring around 5mm, that sounds fine. I'm just referencing the medical standard to provide a frame of reference. If used in an environment where dust or humidity is more likely to get involved, add margin. You can also consider potting or conformal coating, but it looks like you have plenty of space to work with.

ChrisGreece52:
Its a board to replace my recently fried thermostat (my bad). It will be used indoors and enclosed (not fully since i need slots to get the ambient temperature). Another problem i have is clearance between low power stuff (5 Volt traces and components) and mains AC). Will the 3 mm clearance(lets say 4 to be sure) suffice?

TimNJ:
Is the 5V supply in any way user accessible?

Sounds like no. In this case, the standard 3-4mm clearance is okay. You should use a non-conductive enclosure (plastic). If you need to use metal, then you must earth the enclosure.

A couple other things to keep in mind...Where is the 5V rail coming from? Are you using a isolated converter  (with a transformer) or is the 5V rail from a simple non-isolated buck converter directly off the mains?

If the design is not isolated, then you still need to be careful about any controls (knobs or buttons) that are user-facing. Plastic case is good, but be careful about potentiometer shafts, switch actuators, etc. If they are metallic, there may be a fault condition that puts the users in a dangerous situation.

If you are using an isolated design with a transformer, and assuming all controls are on the isolated side of the transformer, then you don't have to worry about the above. However, you do need to be concerned with the level of isolation provided by your isolated AC/DC converter. In this case, it's best to just buy an off the shelf PCB module. But, even with a module, you still need to make sure you have adequate spacing between primary and secondary connections. In this case, most safety standards require at least 5-6mm. Most stringent medical standards need 8mm.


Nusa:
The issue I see is not the lines in parallel, but the point where you cross L and N. At that spot they are separated only by the thickness of the board.

In this case you can easily avoid this simply by running the trace to the relays over the top from the thermal fuse instead of coming from the MOV pin.

Navigation

[0] Message Index

[#] Next page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod