Open Ground gfic outlet - Page 1
Forum section: electronics / beginners

author: Flashlight
author_rank: Newbie
timestamp: November 24, 2018, 09:43:55 pm
content: I wanted to try to learn more about electronics and soldering and was looking at some equipment to buy, but I have a couple questions before I do.I have gfic outlets in my apartment that were upgraded from older 2 prong outlets and they have open grounds, would these be safe enough to use for a 50 watt soldering station?How can I ground my esd mat and wrist strap when I have these outlets? The only thing I can think of is to run a grounding wire across my apartment to where the water lines are.Can I use an oscilloscope safely plugged into these outlets?Thanks for reading this and I appreciate any help you can give me.

author: Ian.M
author_rank: Super Contributor
timestamp: November 24, 2018, 10:16:16 pm
content: Nope. They aren't suitable for powering an electronics workbench. The scope must be grounded for safety (assuming its mains powered with a three wire line cord), the soldering station to prevent its ground leakage current going via the tip and blowing ESD sensitive parts, and you cant trust a waterpipe for grounding in a multi-occupancy dwelling as you don't have access to its full length to check continuity nor control over whether a plumber may make a repair with plastic pipe or an isolating coupler.You could feed your bench via an isolating transformer and use an equipotential bonded zone on the secondary side in place of ground, bonded to the water pipes so your local 'ground' doesn't float at a significant potential with respect to metalwork in the building structure.

author: floobydust
author_rank: Super Contributor
timestamp: November 24, 2018, 10:26:08 pm
content: Multi-occupancy dwellings must have mains wiring in metal conduit, so that is likely how your outlets end up being grounded. In a say 1950's apartment, the metal conduit grounds the junction box and there is no dedicated ground wire.I would carefully measure ACV between the junction box and any plumbing or hydronic heating system pipes. If there are no surprises, I then measure ohms between the grounds.Older apartment buildings have all steel and copper plumbing and this is usually the building ground.

author: 6PTsocket
author_rank: Regular Contributor
timestamp: November 26, 2018, 07:45:05 pm
content: In all probability, the old box is metal. The cable might have been BX ( flexible metal sheath). I would investigate to see if there is a ground in the box. If there is, the gfci or almost all modern receptacles have the ground pin tied to the mounting bracket, that gets screwed to the box. A voltage test between the hot and ground pins of your gfci will tell you if the ground is connected or not.Sent from my SM-G900V using Tapatalk

author: tkamiya
author_rank: Super Contributor
timestamp: November 26, 2018, 09:53:08 pm
content: A couple of things....Running a separate ground as you suggest is against electrical code.Two wire into GFCI works just fine, provided GFCI is fairly new. Older one required ground connection.In fact, using GFCI in a way say is common workaround for older homes with two wire connection.As long as you observe basic electrical safety, 2 prong outlets are perfectly fine for soldering irons and oscilloscopes. It's just that margin of safety is little lower. I used to be a tech in Japan in 80s. Back then, all plugs are two prongs.By the way, I am a licensed electrician. (My license is from Japan and I do NOT practice it)

author: 6PTsocket
author_rank: Regular Contributor
timestamp: November 29, 2018, 05:27:04 am
content: Quote from: tkamiya on November 26, 2018, 09:53:08 pmYou're right. The newer gfcis need no ground. Gfci hair blower plugs are 2 prong. I just thought it was worth seeing if there was a ground in the box. It is better to ground the shell of equipment than to cut the power off because more than 5 ma is going to ground through you.Sent from my SM-G900V using Tapatalk

author: Ian.M
author_rank: Super Contributor
timestamp: November 29, 2018, 06:43:07 am
content: Three pin GFCI protected outlets with no ground are permitted by the US national Electrical Code, and as such are deemed safe for people, pets etc. but they certainly aren't safe for ESD sensitive parts when a soldering station or iron plugged into the ungrounded socket is used.Seehttps://www.eevblog.com/forum/beginners/simple-fet-circuit-for-onewire-protocol-doesn_t-work-as-expected/msg1277272/#msg1277272for one member's experience with blown 2N7000 MOSFETs due to a missing ground to their Hakko FX888D soldering station.Floating a scope by disconnecting the ground is *STRONGLY* discouraged by all reputable manufacturers, because of the shock risk from any etalwork including the input BNCs, grub screws in knobs etc. if the probe ground is ever connected to a circuit node at an unsafe voltage. Engineers who should have known better have died from this, so don't risk leaving your relatives with the job of organising your funeral. Also, there's a small risk of insulation breakdown in the scope's PSU, due to the added stress on the insulation if the chassis is floating at a high voltage, so even if it doesn't kill you, it may damage your scope. Furthermore, you'll get increased mains hum and switching noise from the scope's PSU on your measurements.