Anything I should know about putting GFCIs at a work bench? - Page 1
Forum section: electronics / general

author: cdev
author_rank: Super Contributor
timestamp: April 07, 2015, 04:16:20 am
content: Basically, I have two GFCIs and I am wondering if there is anything I should know about their use in an electronics workbench setting? I am not anticipating any dangerous conditions, actually almost everything I fool around with is low voltage - I'm just planning to replace the current wall outlets with GFCIs, does that sound like a good plan?

author: SL4P
author_rank: Super Contributor
timestamp: April 07, 2015, 05:26:28 am
content: Quote from: cdev on April 07, 2015, 04:16:20 amThe thing you need to know is that you're smarter than most semi-pro elec techs and engineers.Make sure you test the devices before you need to depend on them, and keep in mind that you may want a 'dirty' circuit as well for permanent appliances - like phones & heaters etc that are not in the immediate workspace.Also remember that mains leads that you run over with your chair, or drop the hot iron on - are worthy candidates!

author: kizzap
author_rank: Unknown
timestamp: April 07, 2015, 09:28:05 am
content: In case you haven't figured it out yet, a GFCI will only trip on faults (either Line or Neutral)to EARTH. It will happily supply up to the Circuit Breaker's rated current (which can be upwards of 100A depending on the breaker/time). Basically the GFCI will do shit all if you short Line and Neutral together.I don't know much about the American (and I am assuming you are, happy to be proven wrong), but in Australia you can get RCD(GFCI)/CB combos, which will detect either fault and trip. Might be worth looking into that?

author: SeanB
author_rank: Super Contributor
timestamp: April 07, 2015, 05:55:23 pm
content: In the USA ( that you get GFCI outlets anywhere in the world other than the USA I have never seen) so yes, putting them in is a good thing. I would also recommend that the regular outlets are also replaced with AFCI outlets, as they protect against arcing faults as well. GFCI on stuff to the bench, and AFCI on the rest of the room.

author: Zero999
author_rank: Super Contributor
timestamp: April 07, 2015, 06:10:16 pm
content: GFCI is called RCD in most other parts of the world.I've never heard of AFCI.

author: Ian.M
author_rank: Super Contributor
timestamp: April 07, 2015, 06:22:16 pm
content: The rest of the world calls them RCDs and they are certainly available as sockets in the UK. However we rarely bother as 30mA trip current RCD protection for all outlets is now more-or-less mandatory under our wiring regs. (there are a very few exceptions) and it is commonly done using a whole-house RCD on the incoming supply. This is IMHO dangerous as you loose all the lighting if it trips.More sensitive individual socket RCDs are prone to nuisance tripping, commonly caused by high level common mode noise, so I'd want at least one outlet that didn't have RCD protection (other than any whole house protection that may exist)If you are building a serious multi-station workbench, it may be worth getting a high current circuit run to a high current industrial socket behind the bench then having an appropriately rated flexible lead and plug to a consumer unit (sub-panel / breaker box) with individual arc fault RCB0 breakers for each outlet or station on the bench. That gives you a single point to shut off the whole bench - useful for peace of mind at night, and also the dedicated supply means you have fewer worries about power quality or ground loops. Considering the bench as plug-in equipment, in most jurisdictions you can wire it yourself without a formal electrical inspection, which may not be the case if you replace wall outlets other thanlike-for-like.

author: LabSpokane
author_rank: Super Contributor
timestamp: April 07, 2015, 06:28:50 pm
content: The US standard GFCI is designed to trip about 5mA, not 30mA. They are an excellent idea. Consider grounding your workbench, etc if it is metal. I specifically chose metal pegboard mounted to Unistrut so that I would have a solid ground in case devices mounted there faulted.

author: free_electron
author_rank: Super Contributor
timestamp: April 07, 2015, 06:37:21 pm
content: arc fault interrupter in the fuse box. gfci in the outlets.standard breakers work on a thermal principle. create a short : heat up the internal element and they popAFCI are magnetic. create a hard short and the current spike sets of a magnetic system the pops the breaker. so these things react to huge inrush currents. if you have an intermittent arc a thermal breaker may 'average out' the current and not trip. an AFCI will trip because the arc current is much higher.the american power system is retarded.in europe you can get GFCI + AFCE + breaker in 1 combo element. my parents home is 50 years old and already has such devices installed. AFCI are just now becoming avaialble in the Us but not mandated by code.same stupidity as running double insulated wire inside drywall ... one rodent and the house goes up in flames. power cables need to run in conduit.

author: ajb
author_rank: Super Contributor
timestamp: April 07, 2015, 07:56:33 pm
content: AFCI breakers are actually mandated in all living spaces (so, basically over the entire home) in many parts of the US now. GFCIs are still only required in potentially wet locations, typically. I'd be curious how well the statistics bear out the emphasis on arc fault versus ground fault protection, in terms of actual lives lost to preventable instances of each fault. Given the lower voltages and commensurate higher currents in the US system versus most European systems the difference in emphasis would seem to make sense, but I don't see any reason why both shouldn't be more widely used.

author: AG6QR
author_rank: Frequent Contributor
timestamp: April 07, 2015, 08:15:01 pm
content: Generally, it's better to have a GFCI than to not have one. However, they don't protect against everything, so the presence of one is no excuse to get sloppy about safety.In particular, as Kizzap says, they only protect against faults to earth.As a consequence, if you're using mains to feed an isolating transformer, a GFCI offers no protection whatsoever to anything on the secondary side of the transformer. The GFCI merely insures that the line current going to the primary of the transformer is all returned via the neutral, but the GFCI doesn't "see" anything that's happening to isolated secondary.This sort of situation sometimes comes up on a test bench when someone uses a 1:1 isolation transformer in order to "float" a device under test so that a non-isolated oscilloscope may be used to probe it. If you clip the scope's ground lead onto something that is close to line potential on the DUT, then other parts of the DUT normally at neutral potential may carry full mains voltage with respect to ground. Touching such parts of the DUT while touching something grounded could give you a solid shock of mains voltage, and the GFCI won't prevent it.Of course, without a GFCI, you'd still have the same potentially dangerous situation when using an isolation transformer. The GFCI didn't make anything worse, unless it made you feel invincible and protected, causing you to drop your guard.

author: Zero999
author_rank: Super Contributor
timestamp: April 07, 2015, 10:27:05 pm
content: Quote from: free_electron on April 07, 2015, 06:37:21 pmHere in the UK the standard circuit breakers fitted in homes are magnetic.Is it normally one GFCI per socket in your part of the world? 5mA sounds like a very low trip current, if it's for more than two appliances.RCDs are 30mA here and protect many appliances running from the same circuit. I suppose the higher current isn't so safe but there's less nuisance tripping.

author: LabSpokane
author_rank: Super Contributor
timestamp: April 07, 2015, 11:18:47 pm
content: It's normally one GFCI device per string of outlets that need protection. Our outlets are designed to be daisy-chained. In fact, putting more than one GFCI device on a circuit usually doesn't work. Typicallly only the first GFCI In the series will trip regardless of the fault location.

author: NiHaoMike
author_rank: Super Contributor
timestamp: April 08, 2015, 02:19:03 am
content: Some GFCIs and AFCIs have a tendency to false trip under high noise conditions. Buy from a store with a good return policy.Also, a GFCI will be useless with an isolation transformer.

author: Kevman
author_rank: Regular Contributor
timestamp: April 08, 2015, 04:13:43 pm
content: Quote from: free_electron on April 07, 2015, 06:37:21 pmI'm almost positive that a standard circuit breaker in the US is both magnetic and thermal, regardless of AFCI or not.

author: SeanB
author_rank: Super Contributor
timestamp: April 08, 2015, 04:42:47 pm
content: Older ones are mostly thermal, with only newer ones ( from the 1980's here in South Africa) having in addition to the thermal bimetal a magnetic trip coil. Remember that they only have to trip faster than the wire can overheat. It is only recently that breakers also had to include extra functionality to handle things like small overloads which can overload marginal wiring, and things like user safety and protection against arcing faults in sockets.

author: jlmoon
author_rank: Unknown
timestamp: April 08, 2015, 07:28:14 pm
content: Not sure why anyone would want GFCI breakers on their workbench unless they're working in their bare feet or standing in a pool of water or if you have a metal grounded bench it might be a great idea. But for the most part sounds like more trouble than they are worth.Any slight leakage of suspect equipment you might be working on is going to trip them, adding another unknown to the path of troubleshooting. I prefer to treat all my bench areas as plug in appliances to dedicated and isolated grounds as to reduce the common mode noise and any ground loops that are easy to create.

author: cdev
author_rank: Super Contributor
timestamp: April 09, 2015, 12:00:20 am
content: Actually, I could probably be a poster child for how everything is increasingly low voltage and DC centric.I just think its a kind of matter of principle to have even more- an extra level of protection.

author: gwideman
author_rank: Contributor
timestamp: May 01, 2024, 12:12:44 am
content: Quote from: jlmoon on April 08, 2015, 07:28:14 pmI realize this is rather an old thread, but to answer this point:You are right to observe that the GFCI will only trip on current that "escapes" from the Line-Neutral path. That can easily happen if you inadvertently create a path from any live part of the device under test to a grounded terminal or case of some test equipment, for example a scope.As to a grounded workbench surface -- this sounds like a terrible idea. The user would almost always have some body part in contact with that surface, so any single arm touching a live part of a circuit will always give a shock. Ie: The "One hand rule" would become useless.

author: Psi
author_rank: Super Contributor
timestamp: May 01, 2024, 12:23:15 am
content: This is not GFCI/RCD related but make sure your work-bench/work-room has a master power switch.So you can flip one switch off and walk away with everything powered down.Accidently leaving something on is quite a high fire/safety risk with electronics. Hot air/ soldering irons/ pre-heaters / solder pots / reflow ovens / high current circuits ... All things that get HOT and are able to catch on fire and burn your house down.If you are in the room you can easily stop problems from becoming fires, but if your asleep in another room or out of the house you can't.Just last month my hot air gun slipped out of its holder and was point blank pointing at my wooden desk.It had already made a rather large burn hole in the desk and was well on its way to starting a fire before i noticed the problem and stopped it, and i was in the room.

author: JustMeHere
author_rank: Frequent Contributor
timestamp: May 01, 2024, 02:39:11 am
content: So I had a house that had no earth but a GFCI panel to get it up to code. (Well the bathrooms still had to be grounded, so I had to pay for that.)These things trip when less power comes back in N than goes out on Load.N is connected to Earth in the panel. So it's I'm not sure it can "fault" to Earth. It can become disconnected.I did ultimately run a grounded line to my office. That circuit would trip every time lightning would strike too close.

author: paulca
author_rank: Super Contributor
timestamp: May 01, 2024, 09:12:38 am
content: My office and workbench are on several RCDs.The whole house is on a 100mA trip at the 'tails'. The workbench circuit is power off an inverter with mains transfer switch and RCD.Install them, forget they are there. Maybe, maybe they might save you, but never rely on them.EDIT: I tested my main RCD in anger accidentally one day. I pulled the fuse for the lights with the intent on cutting the light feed wire for the garage out of the 240V circuit and converting it to 12VDC.Fuse out I cut through the 1.5mm T&E and Boom, power off. Why?The cutters shorted N to E, enough potential exists in the voltage drops to cause current to flow. Trip.

author: EPAIII
author_rank: Super Contributor
timestamp: May 01, 2024, 09:59:28 am
content: Why on earth would you deliberately provide 1/2 of a circuit that could kill you?In addition to years as an electronic hobbyist, I worked over 45 years with all types of electric and electronic equipment, including high powered (high Voltage) commercial transmitters. In all of that time the worst shock I ever got was when about 40,000 Volts passed through my body, through my shoes, and into the grounded, METAL workbench I was working at. I know that was the path it took because I found the burn holes in my hand and on the bottom of my foot.IMHO, the last thing you want is a grounded workbench. And I think I know what I am talking about. I don't even like those grounded mats for the top of the bench that are supposed to prevent static damage. When I find one I either disconnect it or toss it away. In that same time period I have never seen anything damaged by static discharge. Those mats serve NO PURPOSE.Oh, and when you see a Voltage specification on a probe, BELIEVE IT. That 40,000 V also went through or around a meter probe I was using. The meter, a Simpson 260, was OK.Quote from: LabSpokane on April 07, 2015, 06:28:50 pm

author: watchmaker
author_rank: Unknown
timestamp: May 01, 2024, 11:59:28 am
content: In my "lab" area (corner of the basement) the bench is powered by (2) 12 output switched 120 v strips. These are in turn plugged directly into a GCGI/AFI which is wired to the panel protected by a whole-house surge protector. After burning up two microwaves in Maryland lightning storms, I learned the value of the latter. Also, I found one of my switched machine tools smoking. Had no problems for ten years after that.I do use an ESD mat/strap on a wooden bench (doors on saw horses, I am a "farmer" at heart); in defense, my setup is temporary as I figure out what I need (MORE space!). But I avoid (emphasis on avoid) probing over 120 vac.This set did save me when I was troubleshooting a BK501a and I knocked the collector of a high voltage transistor to the grounded frame. The GFCI/AFI reacted in time to save the device and scope and the one-hand rule protected me.The central switching at the bench is highly convenient, inexpensive, reduces electricity usage, and adds another layer of equipment protection.As to whether the ESD protection is overkill and risky, I accept current industry practice. This is all as an extremely raw amateur.

author: soldar
author_rank: Super Contributor
timestamp: May 01, 2024, 03:11:04 pm
content: Quote from: free_electron on April 07, 2015, 06:37:21 pmI believe you are confusing things.European and American circuit breakers both can be tripped by a bimetallic element heating up and by a solenoid. The heat element is slower acting and the magnetic element is faster acting. Between the two elements they provide a certain trip time as a function of the overcurrent.GFCI are generally provided in America at the outlet level whereas in Europe they are generally in the general panel. Each option has its pros and its cons.And AFCI are ARC Fault Circuit breakers, totally unrelated to the previous ones.Edit:https://www.realpars.com/blog/circuit-breaker

author: AVGresponding
author_rank: Super Contributor
timestamp: May 01, 2024, 04:39:26 pm
content: The most important thing to remember when you have GFCI/RCD/RCBO protection is thatTHIS DOES NOT MAKE YOU SAFE. It onlyreducesyour risk.

author: JustMeHere
author_rank: Frequent Contributor
timestamp: May 01, 2024, 07:23:59 pm
content: Quote from: EPAIII on May 01, 2024, 09:59:28 amI heard a story just like this yesterday....bench was grounded. Worker was tired. Had one hand on the bench and accidentally brushed a welding rod across his forehead trying to wipe sweat away. Zap.If only his project had been grounded, he would still be here.

author: jonpaul
author_rank: Super Contributor
timestamp: May 02, 2024, 04:40:11 am
content: 55 yrs experience in power electronics to 75 kV and 12 kW.Never needed GFI or AFCI breakers.Nor grounded metal bench120V mains >>10A Variac >>1:1 isolation trsf (Signal 2 KW 120/240 dual DU-2) >>bench, DUTScope is earthed to ground and DUT/SMPS floats.The Arc Flash breakers are junk and usually false trip on EMI.GFI needed ONLY in wet environ, eg bathroom, toilet, kitchen.IF your workspace is in a bassement eg. damp concrete floor,1. Get thick rubber matt2. Wear rubber sole shoes3. Yes ONE GFI per line of outlets may be useful.Be safe,Jon

author: Kasper
author_rank: Frequent Contributor
timestamp: May 02, 2024, 04:48:27 am
content: Quote from: jonpaul on May 02, 2024, 04:40:11 amMine sometimes trip when I turn on table saw or mitre saw. It is very annoying.

author: paulca
author_rank: Super Contributor
timestamp: May 02, 2024, 08:43:54 am
content: Quote from: AVGresponding on May 01, 2024, 04:39:26 pmLike an airbag in a car.

author: nctnico
author_rank: Super Contributor
timestamp: May 04, 2024, 09:43:22 am
content: Quote from: EPAIII on May 01, 2024, 09:59:28 amYou couldn't be more wrong about anti-static mats. ESD damage is real and I have first hand experience with that. Several decades ago I build & sold PCs (using the same brand & type of components) and I used an ESD safe workbench for that. But at some point I didn't have enough space so I assembled a PC at a regular desk and carpet on the floor. Long story short: within a year I had to replace every part of that PC. One thing after another broke. I never had that problem with any of the PCs I built at the ESD safe workbench. That was an expensive lesson.And I do make it a point to run my workbench mains from a GFCI / RCD. All test equipment is grounded so basically you can grab ground at any point on a typical electronics workbench. Equipment gets older and could develop a ground leak or so. So when something mains related fails then at least the GFCI will trip instead of letting the situation get worse and pose a shock hazard to me.

author: soldar
author_rank: Super Contributor
timestamp: May 04, 2024, 10:46:31 am
content: Quote from: EPAIII on May 01, 2024, 09:59:28 amI am here to inform you that you do not know what you are talking about. Ask people in the industry who know about the topic.If you live and work in a location with high humidity and low static then you will get lucky most of the time.If you live and work, like I do, in a location with extremely dry air and lots of static, you absolutely need to take precautions or you will be killing devices every day.I live and work in a location with naturally dry air, add heating in winter and you have extremely dry air. Add insulating flooring and you will walk 10 ft to a door and get zapped when touching the door knob. Guaranteed.In this environment you absolutely need to take precautions and I have killed my fair share of devices.I still remember in the 1970s I bought a digital clock module which cost me a small fortune for me at the time. It had barely made it out of the packaging when I felt the zap that killed it. That taught me to be more careful and less impulsive.

author: tooki
author_rank: Super Contributor
timestamp: May 10, 2024, 08:18:25 am
content: Quote from: EPAIII on May 01, 2024, 09:59:28 amAside from the total untruth about ESD mats written above — they most certainly DO serve a purpose, and the fact that you haven’t identified any damage that you attribute to ESD doesn’t mean you didn’t cause any — there’s a reason they are not made of low-resistance material, and have a further resistor inline to the actual ground: that limits the current in an ESD event, but above all limits the current if the operator were to complete a circuit through it. So if you are touching the mat and touch mains voltage, the current is limited to something so tiny as to be irrelevant.Most hobbyists aren’t working with the types of voltages where the current through an ESD mat becomes hazardous. 40kV is certainly well outside of what most hobbyists should ever consider working on. By that point, one either needs to be highly experienced, or have the guidance of someone who is.(Just the other day, at work, I actually applied 40kV to an experiment apparatus for the first time. It has a custom metal cabinet, precisely to ensure operator safety. But while it is high voltage, unlike your situation, mine is low energy, in that the power supply itself is only capable of 1mA, with the adjustable current limit set lower. Nonetheless we equipped it with two layers of interlocks, as well as a discharge circuit to ensure that the HV cable’s own parasitic capacitance can’t be left with residual charge. Since I am not very experienced with HV stuff, I had the guidance of my old boss, who is. )