Safe to use an unearthed oscilloscope? - Page 1
Forum section: electronics / beginners

author: Anton
author_rank: Contributor
timestamp: February 23, 2015, 06:23:31 pm
content: A brief introduction about myself because this is my first post on this forum.I'm Anton, 21 years old and live in the Netherlands.I've always had a strong interested in electronics. I’ve seen all of Dave’s videos of the last 3 years allowing my interest and skills to grow bigger and bigger.The last year, more and more people come to me with electronics I need to fix. Usually it is going well, but not always. I purchased several different tools, but still very basic. My skills grow, so I'm ready for an oscilloscope. I’m currently looking for a DS1054Z which is according to Dave a good starters oscilloscope.Now on to my question.I live in a house where only in the kitchen are earthed power outlets. So the room where I want to use my oscilloscope has no earthed/grounded power outlets. Is it safe to connect my oscilloscope to an unearthed power outlet? Does it damage anything?I have read on several other forums but it’s not very clear to me. Some of them say that it’s very dangerous to do, but others say it’s safe to use where others say it’s safe but only in certain circumstances.Can someone clarify this to me.Thanks in advance,Anton

author: Simon
author_rank: Unknown
timestamp: February 23, 2015, 06:27:14 pm
content: it won't damage anything but if you connect your oscilloscopes ground to something live you will make the entire scope chassy live and there will be no device to protect you. At the very least use and RCD, it will hopefully save your life. Get your sockets earthed, even if it means you make your own earth and put it in the ground yourself with a wire in through your window or make a hole in the wall or use known grounded water pipes.

author: tautech
author_rank: Super Contributor
timestamp: February 23, 2015, 07:02:38 pm
content: Welcome to the forum.Understand that to properly display any signal the input (probe) must be referenced.The probe reference (GND) lead is only for this purpose.Without a mains earth your reference will be floating at the potential of what ever you connect it to.SO WILL the chassis of your scope and each subsequent probe reference lead.This is a well known practice....Floating Your Scope.....not recomended for novices, beginners or for any HV circuits.All manufacturers advise against using this practice.A comsumer appliance that sits on the shelf without any contact to its user and is double insulated is quite safe but using a scope without a mains earth demands 150% attention for your safety and the scopes.Battery powered circuits fine, anything else, not until you've spent 100's of hours using a scope.A mistake CAN kill you.

author: Anton
author_rank: Contributor
timestamp: February 23, 2015, 07:30:05 pm
content: Thanks for your quick replies.So using an ungrounded oscilloscope is only safe if your now what you are doing. Which is in my case whit my skills definitely not safe! Time to pull some ground wires through the walls and create a proper earthed outlet.You say is safe when using a battery power source. Is it also safe to use an AC or DC adapter? They are usually not grounded either.Anton

author: Zero999
author_rank: Super Contributor
timestamp: February 23, 2015, 07:42:25 pm
content: I would go further an say that using an unearthed 'scope is never safe unless it's specifically designed to do so or is run off batteries.It's not what you might do wrong but also the small possibility the 'scope could develop an electrical fault, causing the case to be connected to the line conductor. This sort of fault can occur with any mains appliance which is designed to be earthed.You should seriously consider getting the house rewired. If you're renting it the landlord should do it for you.

author: 691175002
author_rank: Regular Contributor
timestamp: February 23, 2015, 07:45:33 pm
content: I found that this video was a pretty good overview of the issues involved.http://www.eevblog.com/2012/05/18/eevblog-279-how-not-to-blow-up-your-oscilloscope/

author: tautech
author_rank: Super Contributor
timestamp: February 23, 2015, 07:49:54 pm
content: Quote from: Anton on February 23, 2015, 07:30:05 pmThe trouble with these is each different one will have an unkown potential WRT mains ground.As they are powered from mains and are of unknown quality, you are still exposed to risk.A DMM can be used to check for disparities.

author: Anton
author_rank: Contributor
timestamp: February 24, 2015, 09:16:46 am
content: Quote from: 691175002 on February 23, 2015, 07:45:33 pmYes, this is a very good explanation. I watched it over a year ago i think. So i watched it again it makes sense now. Thanks.Quote from: tautech on February 23, 2015, 07:49:54 pmFor what i've understand from earlier posted video, this is not really a problem. If it's an isolated adapter or the resistance between mains earth and negative is high, its safe right?Anton