Anything I should know about putting GFCIs at a work bench?

[JustMeHere]

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.

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.

I 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.

[jonpaul]

55 yrs experience in power electronics to 75 kV and 12 kW.

Never needed GFI or AFCI breakers.

Nor grounded metal bench


120V mains >>10A Variac >>1:1 isolation trsf  (Signal 2 KW 120/240 dual DU-2) >>bench, DUT

Scope 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 matt

2. Wear rubber sole shoes

3. Yes ONE GFI per line of outlets may be useful.

Be safe,

Jon

[Kasper]

The Arc Flash breakers are junk and usually false trip on EMI.

Mine sometimes trip when I turn on table saw or mitre saw. It is very annoying.

[paulca]

The most important thing to remember when you have GFCI/RCD/RCBO protection is that THIS DOES NOT MAKE YOU SAFE. It only reduces your risk.

Like an airbag in a car.

[nctnico]

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.

You 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.

[soldar]

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.

I 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.

[tooki]

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.

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.

Aside 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. )