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| High Voltage tracks clearance |
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| lmagalhaes:
Hi there, I've seen that I should keep a minimum of 2.54mm of clearance between high voltage tracks and, with through-hole TRIACs I was able to do that. But now I've been asked to switch to surface mount triacs and I'm having trouble in keeping that clearance with the space that I have in the PCB. Is it possible to decrease the clearance with some cuts between the tracks? Here's the before and after https://imgur.com/a/6z6i6E4 Since this is a TRIAC with a TRIAC driver and there's no neutral around, is it still needed to maintain the 2.54mm clearance? Thanks ! |
| MagicSmoker:
This is a situation where the correct terminology must be used - clearance is the distance through air between conductors while creepage is the distance along a surface. There are various regulatory documents that specify the distances required vs. voltage vs. application (medical has different requirements, for example) but a good site that covers the basics is: http://www.smpspowersupply.com/ipc2221pcbclearance.html |
| floobydust:
You need to have proper spacings at least four areas: -Between line and neutral -Between ground (PCB mounting spacers, bolts) and hazardous live traces -Between low voltage control electronics (opto LED) and hazardous live triac traces -Between each triac's channel hazardous live traces For up to 300VAC, overvoltage category II (2.5kV), creepage and clearance is minimum ~1.6mm on a pc board. Assuming no condensation and little dust, single-phase. If your solenoids have high kickback and there is no snubber, I try for >2mm. You need more heatsinking for the triac, there's not enough copper pour. It will heat up with an amp or two. You can rotate the triac 180 so closer to the opto, instead of long traces on the sides. In Altium, make a 1.6mm dia circle. Then drag it around your hazardous live traces to ensure you've got enough spacing. Setting up clearance rules in Altium only works half assed. |
| ejeffrey:
Isolation requirements vary depending on voltage, application, environment, materials, and needed certifications. "A minimum of 2.54 mm clearance" is probably correct for some combination of those, but you need to figure out the right value for your application. I suggest you make sure your number is correct for your application. For example even within a given device isolation from live to neutral (for isntance) has different requirements from line to ground even though they are the same voltage. As far as definitions: clearance and creepage are two different things. Clearance is the physical distance through air between two conductors. creepage is the distance along a surface (e.g., along the PCB). The creepage requirements reflect the possibility of surface contamination or condensation allowing surface tracking. Creepage can be improved by using different materials, working in a less contaminated environment, or cutting slots in the PCB. To improve clearance you actually need to insert a barrier between the signals. One way to to this is to cut a slot in the PCB and then allow a plastic fin from the enclosure to poke through it. Now a potential arc would have to go around the plastic fin -- traveling a much longer distance. |
| Andreas:
--- Quote from: lmagalhaes on September 25, 2019, 05:34:13 pm ---I've seen that I should keep a minimum of 2.54mm of clearance between high voltage tracks and, with through-hole TRIACs I was able to do that. --- End quote --- really? how much is the creep distance directly at the package of the TRIAC? The requirements are generally higher between "life" and "neutral"/"earth ground" as across a switch where the load limits the current. with best regards Andreas |
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