Floating Osilloscope Safety Tips - Page 1
Forum section: electronics / beginners

author: JetBlack
author_rank: Newbie
timestamp: April 28, 2017, 11:06:30 am
content: (Edit: Sorry for the double post, my cat sat on my keyboard)Hi guys! I am about to get my first oscilloscope next week, a Rigol DS1054Z. I've been reading the discussions on the forums on floating the scope and proper grounding for the past few days.I would definitely opt for proper grounding if I could, but my predicament is that our house does not have three prong outlets anywhere, so my oscilloscope cannot be grounded. It is also quite uncommon for any houses in our country, barring the newest ones to have grounded wiring systems.Given that I can't really change the wiring in my house, until we move into a new one, what are the things that I would need to look out for when using the scope with the ground pin connected through a three pin power strip (with an adapter attached) to a two pin outlet?Like what kind of measurements can I safely perform, and what would I need to do to avoid blowing up my scope or my circuits?I primarily work with circuits powered by SMPS (random cellphone chargers))

author: danadak
author_rank: Super Contributor
timestamp: April 28, 2017, 11:23:15 am
content: This might help -https://www.eevblog.com/forum/testgear/floating-oscilloscope/http://www.newark.com/pdfs/techarticles/tektronix/FFM.pdfhttp://www.techni-tool.com/site/ARTICLE_LIBRARY/Tektronix%20-%20IsolatedInputOscopes.pdfRegards, Dana.

author: hammy
author_rank: Unknown
timestamp: April 28, 2017, 11:24:06 am
content: Please ask an electrician to have a look. Show him the place where you want to work with that scope and he can do something about this. It really depends on the circumstances at your place and how the wiring in your house is made.Safety first!

author: yada
author_rank: Frequent Contributor
timestamp: April 28, 2017, 11:47:49 am
content: Quote from: hammy on April 28, 2017, 11:24:06 amI have a feeling that would be prohibitively expensive. I'm sure if their house could have proper and safe wiring they would have already done it.

author: sokoloff
author_rank: Super Contributor
timestamp: April 28, 2017, 11:48:24 am
content: Working on low voltage circuits (leaving the SMPSs intact and only using their output) on a workbench, your risks are practically non-existent (insignificantly different from using a multimeter on those circuits).

author: JetBlack
author_rank: Newbie
timestamp: April 28, 2017, 12:04:10 pm
content: Indeed! I would be working mostly with circuits powered by the output of switch mode power supplies (not taking them apart)

author: hammy
author_rank: Unknown
timestamp: April 28, 2017, 12:28:57 pm
content: Quote from: yada on April 28, 2017, 11:47:49 amSure, but we know next to nothing about the circumstances. Maybe there is an easy solution for just that room, or just one outlet. Maybe there is GND nearby (iron water pipes) or another method including a ground rod is possible. But to find such a possibility you need someone with knowledge about this topic and who can do some measurements.As I said ... Safety first!

author: bitwelder
author_rank: Super Contributor
timestamp: April 28, 2017, 12:32:46 pm
content: You could also consider to have a few sets of rechargeable batteries or powerbanks to power your projects.

author: Ian.M
author_rank: Super Contributor
timestamp: April 28, 2017, 01:13:34 pm
content: Actually the risks of using an ungrounded bench full of test equipment are MUCH MUCH higher than using a hand-held multimeter. The problem is the filter caps in the power supplies. With all equipment with three ppin plugs providing a leakage path from line to their ground pin, although the leakage current for each individual device is regulated to a safe level, the total leakage current from a bench full of test gear could easily reach unsafe levels. You'll aloso have great difficulty making measurements on sensitive circuits due to the massice amount of cappacitively coupled mains hum that will be present. Finally, the risks of zapping delicate chips and boards are greatly increased with no proper ground to connect ESD mats and wrist straps to, and with a significant mains leakage current on your scope ground clips.TLDR: All except purpose-designed floating test gear needs grounding. Rig a ground to you bench or if that's totally impossible, consult aqualifiedelectrician about equipotential bonding.

author: JetBlack
author_rank: Newbie
timestamp: April 29, 2017, 02:53:39 am
content: Thanks bitwelder, the idea of having a bunch of power banks to power my circuits, which would have similar output to the 5V 2A SMPS I usually use, is cheap and very doable. I'll definitely dig up some of my old power banks to use for projects.

author: amirm
author_rank: Regular Contributor
timestamp: April 29, 2017, 03:38:23 am
content: The scope better not use the safety ground for anything other than safety. To that end, you can get GFCI outlet to provide similar safety without earth ground.Providing an isolated safety ground to the bench provides no benefit as the impedance to one at the entrance to the house will be way too high and won't trip any breakers.

author: james_s
author_rank: Super Contributor
timestamp: May 01, 2017, 08:55:14 pm
content: The purpose of the safety ground is to prevent any exposed metal parts from ever becoming live under any circumstances. If an internal fault occurs and a live wire contacts an exposed part, the current will be shunted to ground rather than flowing through the body of a person who touches the equipment. I personally would not worry about it too much though, loads of people manage to use those 3 prong adapters in old houses without grounded receptacles without dying. It isn't ideal but sometimes you just have to do what you can with whatever you have to work with.