Soldering iron grounding - Page 1
Forum section: electronics / projects

author: DerDaniel
author_rank: Contributor
timestamp: August 19, 2023, 12:55:45 pm
content: EDIT:My initital idea is unsafe, so please don't copy anything from it!Hello,I'm building the second revision of my JBC clone and this time I want to design the grounding of the soldering tip properly.The following is my thought process so far:According to IPC-TM-650, the tip should have a resistance of <5 Ohms to PE. To adhere to this norm, I will connect GND of the JBC handle to PE.However, I don't want a continuous short circuit if I'm accidentally soldering a live circuit. Hence I'm puttin a fuse inbetween PE and GND (GND of my board is floating).If this fuse blows unnoticed, I still want some protection against ESD. Hence I'm putting a 1 Meg resistance parallel with the fuse.Lastly, I have some unused pins on my uC and I'm thinking about how I can put them to use for detecting a blown fuse. My idea involves another 1 Meg resistance to an ADC pin and a pullup to VCC (see attachment). However, this means that PE will have some voltage to GND when the fuse is blown, which is not the best solution.My first question, am I on the right track?Second, is the 5 Ohms requirement of the IPC-TM-650 reasonable, or is 1 Meg to PE enough?Third, anybody got some better idea how I can measure a blown fuse?

author: wraper
author_rank: Unknown
timestamp: August 19, 2023, 01:09:42 pm
content: Quote from: DerDaniel on August 19, 2023, 12:55:45 pmNo, you never put fuses on the earth connection. If the fuse blows and the circuit still remains powered, now your soldering iron is a safety risk.

author: DerDaniel
author_rank: Contributor
timestamp: August 19, 2023, 01:52:18 pm
content: Quote from: wraper on August 19, 2023, 01:09:42 pmJBCs have a fuse to PE as well. Are they all a safety hazard?

author: strawberry
author_rank: Super Contributor
timestamp: August 19, 2023, 04:10:12 pm
content: since when 24V was safety hazard?not/grounded soldering tip could potentially damage sensitive pats. due to leakage and unpredictable ground loops. ground workbench too to brake loop. only downside is when circuit is charged (short circuit)that joke about bird sitting on 10kV line...

author: wraper
author_rank: Unknown
timestamp: August 19, 2023, 04:41:33 pm
content: Quote from: strawberry on August 19, 2023, 04:10:12 pmYou will be handling a soldering iron at voltage potential of the circuit that blew the fuse. Dunno why JBC decided to use a PE fuse, I haven't seen any other manufacturer doing so.

author: Gyro
author_rank: Super Contributor
timestamp: August 19, 2023, 05:50:07 pm
content: Quote from: DerDaniel on August 19, 2023, 01:52:18 pmNow I know about it, I'd have to say yes, it is a safety hazard. PE is exactly that, Protective Earth. You can't just disabled by a fuse blowing, it goes against all normal wiring practice where the fuse or other protective device is in the Live.This subject has been discussed before, especially inserting a series resistor, I'm sure a forum search will bring up some hits. Irrc, the general consensus has always been that it is far better to be bringing a safely earthed soldering iron tip into contact with a live circuit, triggering its [Edit: the circuit's] protection, than having the tip inert and finding out that the circuit is live via the solder or tool in your other hand.

author: DerDaniel
author_rank: Contributor
timestamp: August 19, 2023, 06:53:51 pm
content: I was planning to have the fuse be slower and have a higher amperage as the RCD the station will be connected to. But for safety reasons it really seems unwise to have a PE connection fused.I think where I went wrong was to not differentiate between PE and ESD-Ground.So my new question is:How should I connect the soldering tip to the ESD-Ground point?

author: Gyro
author_rank: Super Contributor
timestamp: August 19, 2023, 07:07:27 pm
content: The soldering iron tip should be connected to PE via the soldering iron mains cable. Any ESD protection connection - ESD ground point, ESD mat, wrist strap etc, have a protective current limiting series resistor (typically 1M) integral to the leads.

author: Kryptychon
author_rank: Contributor
timestamp: August 19, 2023, 07:08:14 pm
content: Hi,my Weller WS50 station lets the operator decide how he wants its tip to be connected to earth: There is a 3,5mm head phone jack in the back of the station. You can chose to not plug anything into it, then the tip is not grounded at all or put a plug with the desired resistor value into the jack and your tip is connected to earth with the chosen resistance (which obviously includes 0 ohms as well).I think, depending on what you're doing with your iron having the choice might be desirable.Best regardsKryp

author: Gyro
author_rank: Super Contributor
timestamp: August 19, 2023, 07:13:12 pm
content: Hmmm, PE through a 3.5mm jack sounds equally dodgy.

author: Kim Christensen
author_rank: Super Contributor
timestamp: August 19, 2023, 07:17:27 pm
content: Ground your ESD mat, etc, via the proper resistor (1M ?). Your soldering station tip should be connected to safety ground as per normal.Get an external RCD/GFCI and power your entire bench via that. Test gear, soldering iron, DUT all plug into power-bars which are themselves plugged into the RCD/GFCI.Then if you accidentally start soldering live mains equipment on your bench, the RCD will trip saving your bacon from getting fried.

author: madires
author_rank: Super Contributor
timestamp: August 19, 2023, 07:27:29 pm
content: Yep, the tip should be directly connected to PE. Some soldering stations come with a banana socket (and series resistor) for connecting an ESD mat.

author: strawberry
author_rank: Super Contributor
timestamp: August 20, 2023, 07:09:25 am
content: industrial safety rule is not same as consumerindustrial is predictable but consumer come with variablesone soldering station is designed for industrial in mind and other for consumer

author: bostonman
author_rank: Super Contributor
timestamp: August 20, 2023, 01:22:14 pm
content: QuoteI believe this is for a wrist strap. Your Weller SS50 should have a three-prong plug.The 3.5mm jack allows the user to plug their wrist strap into it (which has a 1 or 10M ohm series resistor). This way any static electricity on the user is dissipated through the wrist strap to Earth ground; and the resistor is there so the user can't be tied directly to PE to avoid being electrocuted.

author: Shock
author_rank: Super Contributor
timestamp: August 21, 2023, 07:23:59 am
content: It's called "Potential Balance" written on the back of Weller stations that have it. It's designed to make/break ground or allow a connection from the tip back to the boards "ground of choice" or add a "resistor of choice" either way or a common esd strap/mat connection point. You don't want to randomly plug a wrist strap in (or anything) without checking how it's connected/wired.