Hi all,
I'm currently laying out a PCB which has mains voltages on it (240Vac). Can anyone tell me what would be a safe seperation between tracks, to avoid any safety problems.
Is it safe to have tracks on both sides of the PCB, crossing each other (approx 1.5mm pcb thickness). Is there any other considerations I'll need to take into account when laying out this PCB.
Thanks, Adrian
I'm currently laying out a PCB which has mains voltages on it (240Vac). Can anyone tell me what would be a safe seperation between tracks, to avoid any safety problems.
Is it safe to have tracks on both sides of the PCB, crossing each other (approx 1.5mm pcb thickness). Is there any other considerations I'll need to take into account when laying out this PCB.
Thanks, Adrian
The capacitive problems alluded to above wouldn't worry me. With mains freq, you would need a LOT of capacitance to have any effect, and then it still wouldn't pose a safety hazard.
My rule of thumb is to keep at least 5mm (.1968503inch) space between mains tracks, to have a safety factor even on dirty boards. I double that wrt signal etc tracks, although I try to keep mains stuff on a separate area of the PCB and not mix it with other parts of the circuit.
Jan Didden
My rule of thumb is to keep at least 5mm (.1968503inch) space between mains tracks, to have a safety factor even on dirty boards. I double that wrt signal etc tracks, although I try to keep mains stuff on a separate area of the PCB and not mix it with other parts of the circuit.
Jan Didden
PCB layout
Hi,
I have never had small signal trax running on the top side of an area with mains on it. But I suppose it can be done as long as there is a minimum of 8 - 10 mm of insulation to ALL mains carrying pads and leads.
However I have alvays prefered to keep well clear of mains on a PCB. On my resent startup PCB for my amp I made a singel sidet layout with as much room as possible from mains to the rest of the cuircuit.
\Jens
Hi,
I have never had small signal trax running on the top side of an area with mains on it. But I suppose it can be done as long as there is a minimum of 8 - 10 mm of insulation to ALL mains carrying pads and leads.
However I have alvays prefered to keep well clear of mains on a PCB. On my resent startup PCB for my amp I made a singel sidet layout with as much room as possible from mains to the rest of the cuircuit.
\Jens
Attachments
See http://www.lamothe-approvals.com/Articles/comparisonofspacing.htm
IEC 60950-1: 2003 asks for a minimum creepage distance of 5.8mm and a minimum clearance of 4mm through air (230V mains). As we are talking here about PCB tracks, we have to use the creepage distance, so minimum 5.8mm.
Crossing tracks on both sides of the board would not be a problem according to this standard, since epoxy it is not air, but nevertheless, if you can avoid it...
Steven
IEC 60950-1: 2003 asks for a minimum creepage distance of 5.8mm and a minimum clearance of 4mm through air (230V mains). As we are talking here about PCB tracks, we have to use the creepage distance, so minimum 5.8mm.
Crossing tracks on both sides of the board would not be a problem according to this standard, since epoxy it is not air, but nevertheless, if you can avoid it...
Steven
Mains voltage on a DIY PCB. Do you really want to do this?
The thing I would worry most about is finger proofing the traces with high voltage on them. You are going to be messing around with this thing and if you have exposed traces with mains voltage on them you will eventually get zapped.
At a minimum here is what you should do:
1: Segregrate all mains wiring from the rest of the circuit board. Do not run any low voltage traces anywhere near (beside or over the top of) the mains traces.
2: Keep the mains traces as short as possible (run them directly from the power inlet to the PCB mounted transformer).
3: Install fisch paper (or a sheet of plastic insulator material) on the trace side of the board using standoffs and screws to cover all traces that are carrying mains voltage. If you can get your finger in contact with a mains carrying trace then you have a problem.
4: Use mains rated terminations to the PCB. Soldering a wire into a hole in the board is not acceptable (soldered wires break).
A much better way for a DIYer to deal with AC power wiring is to avoid PCB mount transformers entirely. Use a self contained transformer (toroidal's are nice), wire point to point with mains rated wire and use heat shrink tubing on all mains wire termination. Take your time and be very sure that what you have done is safe.
Phil
The thing I would worry most about is finger proofing the traces with high voltage on them. You are going to be messing around with this thing and if you have exposed traces with mains voltage on them you will eventually get zapped.
At a minimum here is what you should do:
1: Segregrate all mains wiring from the rest of the circuit board. Do not run any low voltage traces anywhere near (beside or over the top of) the mains traces.
2: Keep the mains traces as short as possible (run them directly from the power inlet to the PCB mounted transformer).
3: Install fisch paper (or a sheet of plastic insulator material) on the trace side of the board using standoffs and screws to cover all traces that are carrying mains voltage. If you can get your finger in contact with a mains carrying trace then you have a problem.
4: Use mains rated terminations to the PCB. Soldering a wire into a hole in the board is not acceptable (soldered wires break).
A much better way for a DIYer to deal with AC power wiring is to avoid PCB mount transformers entirely. Use a self contained transformer (toroidal's are nice), wire point to point with mains rated wire and use heat shrink tubing on all mains wire termination. Take your time and be very sure that what you have done is safe.
Phil
Excellent advice, thanks everyone.
It turns out the layout was a bit simpler than I expected. All of the traces are on the underside of the board, thick, short and well seperated. I had planned a MOV from the start, and the 'fisch paper' (I think I know the stuff you are referring to...) is a good idea and will be used.
The only last concern I have is the only live part left accessible to fingers (actually, MY fingers) is the fuse holders. Can I get PCB mount, fully insulated fuse holders?
Oh, regarding the MOV, am I right in thinking it should be placed after the fuses, so if it is triggered, the increased current will blow the fuses?
Adrian
It turns out the layout was a bit simpler than I expected. All of the traces are on the underside of the board, thick, short and well seperated. I had planned a MOV from the start, and the 'fisch paper' (I think I know the stuff you are referring to...) is a good idea and will be used.
The only last concern I have is the only live part left accessible to fingers (actually, MY fingers) is the fuse holders. Can I get PCB mount, fully insulated fuse holders?
Oh, regarding the MOV, am I right in thinking it should be placed after the fuses, so if it is triggered, the increased current will blow the fuses?
Adrian
I've decided that the fuse holders will be the type that mount on the rear panel and you unscrew a cap to get access to the fuse. This removes the last of the problems with 'accessibility to the dangrous stuff'. All remaining mains voltages on the PCB are on the underside.
Just for interest, the reason I'm doing this is I'm building a 4 channel Leach amplifier, and I'm implementing a soft start circuit. It has two relays and a power resistor, One relay switches on the mains power to the power transformers, but via the 15 ohm power resistor. 1 second later, the other relay bypasses the resistor, allowing full power to the transformers. The relays (and several other functions) are controlled by a PIC microcontroller. The relays are, of course, suitably rated for mains voltages
Adrian
Just for interest, the reason I'm doing this is I'm building a 4 channel Leach amplifier, and I'm implementing a soft start circuit. It has two relays and a power resistor, One relay switches on the mains power to the power transformers, but via the 15 ohm power resistor. 1 second later, the other relay bypasses the resistor, allowing full power to the transformers. The relays (and several other functions) are controlled by a PIC microcontroller. The relays are, of course, suitably rated for mains voltages
Adrian
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