Protection from mains - Page 1
Forum section: electronics / beginners

author: listener
author_rank: Newbie
timestamp: August 11, 2017, 07:17:49 pm
content: Hello everyone,I was wandering is there (probably there is) something that I will connect to mains socket that would protect me if I'm working on mains project and want to test it (of course it could be fuse) but I'm thinking of something convenient possibly adjustable that you can connect to wall socked and then connect your socket to it and if you touch wrong things that it just breaks connection thus saving your life:)I'm just maybe overly cautious beginner but its something that I think would be convenient for me.Thanks for not trashing

author: floobydust
author_rank: Super Contributor
timestamp: August 11, 2017, 07:44:30 pm
content: I do not know about Europe, in North America we haveground fault circuit interrupter (GFCI)which shuts off power if a small current flow to ground is inferred. This protects you against electric shock.Electrical Safety Codes requires them for bathrooms, kitchens, outdoor outlets etc. Because you can spill water and get a shock, or run over your lawnmower cord etc.Here (in North America 120VAC stuff) we can also buy them already built into power-bars. You must something similar for sale? I use one to supply my workbench.Second, even with a GFCI you can have large current flow if a fault occurs. So to protect against fire and burns, you need something to limit available power, like a fuse. Some people use series incandescent light bulbs. If you can even buy them in Germany lol.If you want to work on a mains project, I would suggest both a GFCI and small fuse (a few amps) after.I think some British power-bars or cords have a 16A fuse, so perhaps Germany has them (fuses in mains cords/power bars) and you can put a smaller value fuse.

author: Vtile
author_rank: Super Contributor
timestamp: August 11, 2017, 07:58:40 pm
content: First thing to learn about fuses. In 99 times of 100 they aren't designed to protect you, but preventing the house to go smoke in the air.Second thing is that most of the devices need more current than which is needed to kill you in bad situation.Third RCD (FI in Germany?) doesn't prevent you getting killed from continuous electrical shock if you happen to attach yourself between phase (Line/mains/hot) and neutral (zero) conductors. It doesn't even notice.What kind of device you are working on? There is many things involved when doing it right. A few examples:- Do not work tired. .. no just don't do it. Not even quickly.- Don't do it quickly.- Someone should be around and know what to do if something happens.- Work one hand on the pocket.- Don't use conducting (metal) work table, ie. machinist table is not for electrical or electronics work.- Discharge all capacitors before working on the circuit again.- Do not probe live circuit- Do not touch live unprotected equipment- Keep distance to all grounded objects (water pipes, grounded unnecessary equipment)- Clean your working place before working with mains- Do not work at the edge of the table- Do not work while sitting.- Use proper equipment for the job (differential probes, isolation transformers, shielded cables and connectors etc.)- Test your voltage indicating device from known live circuit before starting your work, if in doubt test it again.- Keep account which parts have dangerous voltages, if unsure measure with good DMM / voltage indicator.- In event of distribution blackout, do not touch anything in your workbench. Take your device out of mains (take a plug out of the socket).- etc.

author: listener
author_rank: Newbie
timestamp: August 11, 2017, 08:40:56 pm
content: Thank you for explanations.I was just looking ElectroBOOM video about GFCIand you are right incandescent light bulbs are thing of history haven't seen any in quite a while maybe someone has it still working at home.I think I have some power cords with fuses in them so replacing them could be something.I'm currently making power supply as pet project.And while maintaining common sense precautions when working with mains I was just thinking it would be nice to have something as last resort something where you can plug your project and set limitations while testing. Of course like you say probably most of things that you plug in to mains will use more current then needed to kill you but it would be nice to have something as last resort in some cases.I guess second power supply

author: Rerouter
author_rank: Super Contributor
timestamp: August 11, 2017, 09:01:27 pm
content: The best protection from mains out there, is approaching it with respect, setting up what you need to measure before turning the thing on, and calling in a friend (case of beer?) to whack you off the thing with a broom handle if you start twitching in a weird way.

author: bd139
author_rank: Super Contributor
timestamp: August 11, 2017, 09:07:45 pm
content: GFCI stops the person who tries to drag your unconscious body already in cardiac arrest off the live circuit from getting killed too. It can be too late for you by the time it has tripped. You're lucky if you didn't get killed and doubly lucky if you had a near miss and a paramedic can get your heart beating properly. All it does is stop the problem escalating or persisting after the event takes place.Isolation transformers (1:1 transformers) save more lives than GFCI/RCD do in a lab environment. Plus strict procedure (one hand in pocket, don't probe live etc), interlocked mains connectors / cabinets etc. Oh and a big STOP button which cuts power to the entire bench/lab.At home I do work on the mains. I have an isolation transformer, master switch and a first aider who knows what to do (the wife) present at all times. Never work alone.Most of the stuff I work on which has exposed mains supplies and traces (fluke bench meters for example) will have the power supply disconnected entirely and brought up on a bench supply instead of actually the mains supply.

author: listener
author_rank: Newbie
timestamp: August 11, 2017, 09:22:14 pm
content: Essentially what you are saying only clear head and safety procedures.And of course someone to detach you, disconnect power and turn off lights:)This thread went a little black.

author: Zero999
author_rank: Super Contributor
timestamp: August 11, 2017, 09:23:39 pm
content: Incandescent lamps will always be available for use in ovens, where nothing else will survive.Both isolation transformer and RCD/GFCIs have their place but neither will protect you from a shock from phase to neutral. The advantage with an isolation transformer, is no current will flow from mains to earth, the downside is that, if one side becomes earthed, you lose that protection. An RCD provides some protection, but you can get quite a nasty shock, before it will trip. If you go for the isolation transformer, a leakage detection circuit, which will light a neon lamp, to warn you if one side becomes earthed.