# `tn-pcb` ### spark gap [:link:](https://eevblog.com/forum/beginners/what-is-a-spark-gap-and-why-we-need-it-on-a-pcb/) - crude technique to protect against ESD (electro static discharge) - ~2kV, varies with atmosphere - carbonization degrades spark gap (sharp point are more prone) ![](https://i.imgur.com/b63DgRe.png =x200) ![](https://i.imgur.com/3unV06u.png =x200) ![](https://i.imgur.com/Nr3YnYV.png =x200) EEVBlog https://www.youtube.com/watch?v=vfP_65gSSBU ### creepage protection - emtpy space or slot - rule of thumb: 4mm slot between mains/primary and secondary ![](https://i.imgur.com/36zBo09.png =x200) http://www.righto.com/2014/05/a-look-inside-ipad-chargers-pricey.html?m=1 ![](https://i.imgur.com/EMideFv.png) ### current-sensing resistor - good tolerance (0.1%..1%) - very low R, high P rating ![](https://i.imgur.com/ib3hGpj.png) ![](https://i.imgur.com/m3vzXpe.png) https://components101.com/articles/what-is-current-sense-resistors-types-specifications-and-selection ### solder(able) jumper ![](https://i.imgur.com/tmRVm6j.png =x200) [🔗](https://www.youtube.com/watch?v=uOp_2-7_1Hw) ### 0 Ohm resistors for configuration ("strap") ![](https://hackmd.io/_uploads/SkMhnVkbn.png =x200)