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Topic: Practical clearance for 220 VAC on PCB (Read 5640 times) previous topic - next topic

be80be

#15
Dec 16, 2012, 12:56 am Last Edit: Dec 16, 2012, 01:03 am by be80be Reason: 1
What you have to understand here is that the four pins which your looking at are on one side of the power line a piece of the line so to say and the Current Sensor is on the back four pins to give isolation

SouthernAtHeart

I think I got it--the isolation is from the VAC and the low voltage DC circuitry, but the AC to AC traces doesn't need as much isolation?  I see this on the picture of the relay you showed, it's got plenty of isolation between the AC and DC circuit, but the two AC pin (in and out) are much closer. 
This was my main problem, getting 6.4mm between AC & AC traces on the board.  So I need 6.4mm between the AC and DC circuitry, how much between the AC legs?  Is there a chart for that?  Judging by the AC current sensor that had AC-IN and AC-out on the four pins of one side of the SOO8, they only had 1mm. I can get probably 3 without any trouble, but if there was a chart of something, I'd like to see it, to understand more about this...
Sure appreciate the the info on this!

jwatte

Quote
I still don't know how they can have 2 pins next to each other on an SOO8 package having large voltages on them


Because it takes many kilovolts to jump a gap that size. If there's a transient on the mains line, it may arc from one of the pins to another, but that's actually not particularly common.

Also, the separation between the control (low-voltage) side and the controlled (high-voltage) side is bigger than the separation between the controlled (both high voltage) areas. And it's a 120V part, not a 240V part. (still, I might have run that lead under the package a little further away from the 120V if I could.)

dc42


I still don't know how they can have 2 pins next to each other on an SOO8 package having large voltages on them...


What matters is the voltage difference between pins or traces. Those 2 pins have the same voltage on them (to within a fraction of a volt). OTOH on that board they haven't achieved as large a separation between the two sides of the chip as they could have (for example, they have routed a trace under the chip). So the board probably doesn't achieve the isolation voltage rating that the chip is capable of.
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be80be

#19
Dec 18, 2012, 02:30 am Last Edit: Dec 18, 2012, 02:33 am by be80be Reason: 1
Hey SouthernAtHeart I found a great site that has all you need to no about http://creepage.com/ and read this one too http://circuitcalculator.com/wordpress/2006/12/19/tips-to-avoid-arcing/
figure you may want a look

O mod my broad after what I've seen 

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