Main Traces on PCB layout

[Wp100]

Hi,

A friend sent me a copy of the pcb they were designing and its passing 240v AC out to the 5mm spaced connectors, max current 2A per connector.

I've little experience of trace clearances, but do wonder about the clearance between those 5mm pins and also where the L and N tracks crosss over , though separated by the thickness of the ds pcb. could that lead to overheating, induction ??

Also there are no mains input or output fuses, which I would have though was a serious oversite.

Any comment welcome, as I never advise folk on handling mains designs.

thanks

 

[dknguyen]

m spaced connectors, max current 2A per connector.

I've little experience of trace clearances, but do wonder about the clearance between those 5mm pins and also where the L and N tracks crosss over , though separated by the thickness of the ds pcb. could that lead to overheating, induction ??

Also there are no mains input or output fuses, which I would have though was a serious oversite.

Where do the L and N tracks cross over? It looks like they're labelling the same trace?

Are you asking about coupling between traces running on opposite sides of the PCB running over each other? It's not an issue at 60Hz unless the traces run in parallel for many meters. And if they cross at 90 degrees that minimizes any crosstalk that could occur.

Or are you talking about capacitive coupling between adjacent pins? If so, 60Hz is way too low to really worry about parasitic capacitive coupling. And 5mm is pretty far away too.

 

[DerStrom8]

What is the copper weight of the traces?

Assuming 1 oz, you're going to want traces 2 mm thick at minimum. As for spacing, IPC-2221B recommends a minimum of 2.5mm between conductors, so 5mm spacing should be sufficient. You should definitely encourage using a fuse at the very least, if not a couple of MOVs as well.

Don't forget creepage protection between the mains voltage and low-power circuitry. Pull the copper way back and cut slots in the board around the high voltage nodes.

 

[AnalogKid]

The thickness of a 0.62" pc board is more than enough to satisf safety agency rules for 240 Vac. For the spacing between conductors and pads on the same layer, called the creepage distance, check UL/EN 60950. I *think* the min spacing between mains conductors is 2.0 mm, but the last time I put a project through an audit was a while ago.

Note - this distance is measured at the closest possible points on traces and/or pads, *not* the center-to-center spacing of the connector pins.

ak

 

[DerStrom8]

I *think* the min spacing between mains conductors is 2.0 mm

Yep, this seems consistent with IPC-2221 as well.

 

[kubeek]

The thickness of a 0.62" pc board

I think you mean 0.062"

 

[AnalogKid]

oops

although, technically, what I said was not incorrect ...

 

[ronsimpson]

what I said was not incorrect

Politician

 

[ronsimpson]

So we decided the spacing is good.
Years ago I spent too many hours trying to get the spacing. I modified one connector's traces to get more space.

 

[AnalogKid]

Politician

Engineer with a functioning sense of humor.

 

[unclejed613]

i would also add fuses... or if the board is in an enclosure, a fuse holder in the case. very often i see an "idiot-proofing" fuse (a soldered-in BelFuse or resistor fuse) on the PCB in consumer equipment. if the user replaces, for example, the fuse in the fuse holder after it's blown because of a fault, and uses a fuse that's 20A instead of the original (which may be anywhere from 1 to 5A in most cases), the fuse on the circuit board (usually 0.5 to 1A more than the fuse in the holder) blows, and so the damage doesn't spread much from the original failure.

but, nothing is completely idiot proof, because some idiots can be very clever.

 

[DerStrom8]

but, nothing is completely idiot proof, because some idiots can be very clever.

As my old signature used to say:

A common mistake that people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools.

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