Hobbyist safety advise when working with AC - Page 1
Forum section: electronics / beginners

author: gkmaia
author_rank: Frequent Contributor
timestamp: February 05, 2019, 02:16:07 am
content: Hi,Just looking for an online course or a good book about safety when working with AC.As a hobbyist I've been working on quite a few things most of them low voltage DC. But now and then I get myself around something that connects to 220V.I have read as many articles about safety around AC and they all talk about the same which is fine and I try to follow them all. But I think I could learn more around it.So... I am looking for a good book or online course with some solid tips on how to stay safe, where the dangers are, security equipment, gear, etc...

author: rstofer
author_rank: Super Contributor
timestamp: February 05, 2019, 03:04:27 am
content: Here is a publication by our state's safety enforcement agency:https://www.dir.ca.gov/dosh/dosh_publications/Electrical_Safety.pdfThere are links to other documents like the formal regulations imposed on industry to help protect their employees.Note that you will find rules regarding Personal Protective Equipment like gloves, flameproof attire and safety shield - depending on voltage level.I think you might want to work downstream of a Ground Fault Circuit Interrupter (or local equivalent) and stay away from electrical distribution equipment altogether.There's a lot involved in staying alive in the electrical business but the biggest factor in getting to retirement is LOTO - Lock Out, Tag Out and the associated testing techniques for proving a circuit is deenergized.I think you need a better training program than arbitrary YouTube videos...

author: wraper
author_rank: Unknown
timestamp: February 05, 2019, 03:23:06 am
content: 'Keep one hand in your pocket' and certainly use GFCI. The major thing is avoiding possible current path through you. So it's not a very good idea to poke onto live circuit with both hands simultaneously. Also you need to be very careful using oscilloscope, don't attach it to anything under mains voltage unless you really understand what you are doing.

author: joeqsmith
author_rank: Super Contributor
timestamp: February 05, 2019, 03:49:20 am
content: Quote from: gkmaia on February 05, 2019, 02:16:07 amSearch "doe energy safety pdf" on Google. DOE has a fair amount of information.

author: james_s
author_rank: Super Contributor
timestamp: February 05, 2019, 04:14:14 am
content: The main thing is don't come into contact with energized conductors. Don't poke around inside equipment with power connected unless it is absolutely necessary.

author: gkmaia
author_rank: Frequent Contributor
timestamp: February 05, 2019, 08:08:00 am
content: Quote from: wraper on February 05, 2019, 03:23:06 amAll my gear and things I work only use power from my wall RCD outlet. I know it cut off power on 30ms, a 1/30 of a heart beat which is a good thing. But I do use a battery powered scope or mutimeter when poking these live things.Also how effective is an RCD in case my scope ground wire accidentally touches a live part of the circuit I am testing?One option would be to buy a differential probe but that is quite expensive. The other could be an isolation transformer to isolate the equipment I am testing. Could you comment on pros and cons of both options?Would this be an option?https://www.ebay.com/itm/1500-Watt-Voltage-Converter-110-to-220-Volt-Step-Up-Down-Power-Transformer-Sale/264077265758?hash=item3d7c3b4b5e:g:CGQAAOSwCtJaTcd-

author: gkmaia
author_rank: Frequent Contributor
timestamp: February 05, 2019, 08:11:39 am
content: Quote from: rstofer on February 05, 2019, 03:04:27 amYes you are correct. I am not counting on blog posts or youtube videos to get this kind knowledge.I need something more academic.

author: capt bullshot
author_rank: Super Contributor
timestamp: February 05, 2019, 08:20:04 am
content: Quote from: gkmaia on February 05, 2019, 08:11:39 amThere's no course or education to beat your personal experienceOnce you've accidentally touched some live wires, you'll know to avoid them.Once you've blown up some traces on a PCB by using an earthed scope, you'll know to use a diff probe or an isolation transformer (always on the DUT, never on the scope).

author: StillTrying
author_rank: Super Contributor
timestamp: February 05, 2019, 08:59:56 am
content: When measuring 230V, keep the rest of your body well away from any earths/grounds.I hate having to hold a probe in each hand at those voltages, so I've got very good at holding both probes with one hand, chopsticks style.

author: tautech
author_rank: Super Contributor
timestamp: February 05, 2019, 09:08:17 am
content: An isolation transformer can be useful to power the DUT and in doing so the Live Neutral supply configuration is converted to Live and Live but only with respect to each other and not to mains ground.Quote from: StillTrying on February 05, 2019, 08:59:56 amStill, it's a good idea to get some clip on leads, at least for one of the DMM leads so that your reference lead is fixed and you can then probe freely with lower risk of a slip and subsequent fireworks.

author: Shock
author_rank: Super Contributor
timestamp: February 05, 2019, 08:19:53 pm
content: Read this whole chapter until you understand all the concepts.https://www.allaboutcircuits.com/textbook/direct-current/chpt-3/importance-electrical-safety/Quote from: gkmaia on February 05, 2019, 08:08:00 amDraw the circuit out (best way to learn). You want all your test equipment on RCDs even an isolation transformer if you have one.The RCD will definitely not save you in all situationsbut can help with equipment failure or if you accidentally trip it you can hopefully limit the damage to you and your equipment.QuoteBattery power oscilloscope with appropriate rating and isolated insulated inputs (handy).High voltage active differential oscilloscope probe (bandwidth limited to probe, isolates and lowers voltage to the oscilloscope input).Isolation transformer (doesn't isolate high voltage from the oscilloscope probe/input, isolates DUT from mains*)High voltage probe (allows you to measure high voltages i.e. 40kV with the appropriate probe, can be very limited bandwidth)Note: They all require you know what you are doing but with an isolation transformer you can easily undo any perceived safety by attaching additional equipment (one of many ways in fact). You should not rely on any device to keep you safe it's more about knowledge and a systematic approach to safety.The link you posted is an auto transformer, it has no isolation. Isolation transformers have various different wiring schemes. I've not seen a suitable purpose built isolation transformer for sale here in Australia. We refer to ours as a bench safety isolation transformer or a technicians isolation transformer, ours are wired with the intended purpose of providing a fully floating mains source. A medical grade (or quality) isolation transformer may have additional safety features. But never assume anything is quality or is ever wired correctly because they often aren't.I'll add a tip to those provided, always know the circuit you are probing and where the different voltages are, you can easily exceed your equipments input and less likely to learn what a Cockcroft–Walton ladder is the hard way.

author: Mechatrommer
author_rank: Super Contributor
timestamp: February 05, 2019, 11:33:38 pm
content: Quote from: gkmaia on February 05, 2019, 08:08:00 amthe chance you get electric shock is higher when there is exposed gnd on the unit and you touch that while gnd clip connected to circuit. with bench scope, the gnd clip will be connected to earth and if you connect that wrongly, RCD will trip."fool" proof precaution:1) wear insulating gloves2) wear insulating boot3) as mentioned RCD/GFCI/ELCB"fool" means you can be a fool and still live.also as food for thought, when you get a shock, your muscles tend to contract meaning your joints will tend to close down or elbow and shoulder to pull up. so when working with mains, if you see naked wire crossing or entering those "shock" or "reflex" path, you should stop and tidy up, its means you are working in a mess condition. for example if you get a shock your hand will grasp or fist, if there is naked wire in the middle, you will unintentionally grab that and you are in deep sheet, even if your other hand safe in one pocket. maybe its not very clear until the best guru ie the shock itself comes to you, it will make you sit and think for a while what was happening and how to avoid that in the future. but remember the "fool" proof hint above, esp the RCD/GFCI/ELCB thing, do not underestimate that, i think it saved me few times while working in a "mess" conditions.

author: MadScientist
author_rank: Frequent Contributor
timestamp: February 05, 2019, 11:52:10 pm
content: An the OP give us a bit more on the specifics AC safety is a huge topic and really we need to scope out what you intend to do

author: vk6zgo
author_rank: Super Contributor
timestamp: February 06, 2019, 01:16:59 am
content: Quote from: rstofer on February 05, 2019, 03:04:27 amA hobbyist is most unlikely to mess with electrical distribution equipment in Australia.It is illegal, for one thing.Even playing with Mains electric wiring inside equipment is a bit in the "nudge, nudge, wink, wink" category.It is still technically forbidden, but so many hobbyists do it, the authorities pretty much turn a blind eye.

author: james_s
author_rank: Super Contributor
timestamp: February 06, 2019, 01:24:10 am
content: How could they possibly stop someone? It's certainly common practice in most parts of the world for people to do things like replace the a plug or lampholder on a table lamp. Simple electrical repairs like replacing a switch, receptacle or light fixture are also very common DIY projects. Well within the abilities of typical homeowner provided they take the time to read the instructions. We're not talking replacement of the service panel or major remodeling.

author: kenneth1212
author_rank: Newbie
timestamp: February 06, 2019, 05:27:11 pm
content: The RCD will not trip if you touch live and neutral. Only live and ground.Skickat från min SM-G960F via Tapatalk

author: aheid
author_rank: Regular Contributor
timestamp: February 06, 2019, 07:10:32 pm
content: When changing a switch or similar simple jobs, I make sure to a) measure the voltage between the conductors, and between the conductors and ground to make sure it's all off before I start and b) not be alone while I'm doing it.If I were to work on circuits involving mains I'd have some very easy way to cut all power, and make sure to wear safety glasses, wouldn't want shrapnel from a capacitor blowing up or something ruining my eyesight.

author: malagas_on_fire
author_rank: Frequent Contributor
timestamp: February 06, 2019, 11:55:48 pm
content: if you are planing to shoot some videos be sure to include some warning signs of electricity or even off camera to prevent someone to mess around and get zapped in the process.For example print one of these or more:https://www.publicdomainpictures.net/pt/view-image.php?image=109279&picture=danger-high-voltage-warning-signAnd plastify with tape used on orders on both sides.

author: max_torque
author_rank: Super Contributor
timestamp: February 07, 2019, 08:04:35 pm
content: It's worth considering there are two main, and rather different reasons for someone to receive an electric shock:1)They deliberately touch a conductor that was live (compared to their body "earth" reference) when they thought it wasn't liveand2) They accidentally touch a conductor that they knew to be live due to making a mistake or errorProtecting against those two events is really quite a different challenge. Preventing the first one comes down to proper knowledge, preventing the second comes down to proper working procedures!i like to use a variac or similar as well as an isolating transformer for "Messing around" with AC voltages, simply because it gives you the ability to slowly ramp in the supply, and to reduced it when you are probing around. A lot of circuits will happily run (at reduced power) on a lower AC voltage, which intrinsically brings a lower risk of serious electrocution whatever the circumstance....