Author Topic: Oscilloscope and no proper grounding  (Read 8998 times)

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Offline Zbig

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Oscilloscope and no proper grounding
« on: July 02, 2013, 07:33:52 pm »
Hello everyone

Tomorrow I'm getting my first DSO. I'm living in an old building with no grounding circuit (230V part of the world). Some of the sockets in my appartment are "zeroed" (have their grounding prongs bridged with Neutral), some don't have GND prongs at all. The socket I intend to connect my DSO to (and the one most of my DUTs will be powered off) is the "no grounding prong" type. Now, I have two options:
  • Install a normal modern socket and then "zero" its GND prong (short it to N)
  • Leave it as it is (essentially "floating" my DSO in the process, right?)

What would be your suggestion, guys? Which option is less bad?

Regards,
Zbig
« Last Edit: July 02, 2013, 07:36:16 pm by Zbig »
 

Offline c4757p

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Re: Oscilloscope and no proper grounding
« Reply #1 on: July 02, 2013, 07:48:42 pm »
I suggest you find a third option. I won't even give one the credit of being "less bad", but you can extrapolate that from "never ever ever ever use neutral as ground".
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Offline IanB

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Re: Oscilloscope and no proper grounding
« Reply #2 on: July 02, 2013, 08:13:10 pm »
There is no good option here. Every piece of electronic test equipment you buy will come with a three pin grounded plug and will expect the ground pin to be connected to a proper mains ground. An electronics lab needs to be fitted with three terminal mains sockets having a proper ground connection.

Some reasons for this, apart from safe use of the equipment so designed, are control of floating voltages and static potentials. Your soldering station will connect the iron tip to ground to stop it damaging sensitive devices. If you are working with sensitive devices (basically anything CMOS), then you should have a static dissipating work mat and wrist strap, both also connected to ground. That keeps everything on your workbench at the same equal potential. Sparks won't fly from your hands and your components will be safe.

You should contact an electrician and see if the sockets in your lab can be made proper.
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Offline Paul Price

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Re: Oscilloscope and no proper grounding
« Reply #3 on: July 03, 2013, 12:10:25 am »
Take a look at these posted topics for more insight on the subject:

https://www.eevblog.com/forum/beginners/is-it-safe-to-use-a-bench-power-supply-not-grounded/

https://www.eevblog.com/forum/beginners/new-lab-no-grounded-outlets/]https://www.eevblog.com/forum/beginners/new-lab-no-grounded-outlets/

There is a lot of hysteria about grounding and ungrounded equipment, you should read the rants and reason of the above link.

Personally, I use all my equipment without 3-wire grounding, as is the practice in my country, and with caution and common sense, and following the essential rules of handing electrical equipment, I have had no problems.
« Last Edit: July 03, 2013, 12:18:09 am by Paul Price »
 

duskglow

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Re: Oscilloscope and no proper grounding
« Reply #4 on: July 03, 2013, 04:24:36 am »
Ah, no, here we go again.  My best suggestion is to completely discount anything Paul Price has said on this topic, as without comment as to whether his advice is correct in *his* situation it's rather dangerous in most contexts, and take the advice above and contact an electrician and see if you can get your lab properly grounded - or at least ask for his/her advice on the topic.  Even if you choose not to ground your lab, that zeroing sounds awful dangerous.
 

Offline madshaman

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Oscilloscope and no proper grounding
« Reply #5 on: July 03, 2013, 04:37:06 am »
I suggest you find a third option. I won't even give one the credit of being "less bad", but you can extrapolate that from "never ever ever ever use neutral as ground".

Yeah, 'cause it's not.  For all you know neutral could be +80V relative to local earth, then all you s**t gonna zap you when you touch it.  It might even be intermittant just to make it more fun.
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Offline c4757p

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Re: Oscilloscope and no proper grounding
« Reply #6 on: July 03, 2013, 04:53:19 am »
Paul, there is a difference between an ungrounded toaster and an ungrounded oscilloscope. One connects to external (often faulty) circuits. I don't know about you, but I like to know what potential it's at. Just brushing up against something else could change that. Leaving it floating, where you don't truly know unless you measure between all your test equipment every time you make a measurement, is reckless. I'm glad it's worked for you, but you endanger people who are not necessarily as mistake-proof as you by suggesting they defeat the safety of their equipment and rely on "caution and common sense". No, grounding doesn't make things inherently safe, but it eliminates a large part of the safety decision-making process.

The grounding pin wasn't stuck on the plug because three's a lucky number.
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duskglow

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Re: Oscilloscope and no proper grounding
« Reply #7 on: July 03, 2013, 04:55:55 am »
Put another way, if you could please stick to giving bad advice wrt questions that couldn't get someone hurt or killed by following it, that would be much appreciated, kthxbye.
 

Offline vk6zgo

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Re: Oscilloscope and no proper grounding
« Reply #8 on: July 03, 2013, 05:08:54 am »
Hello everyone

Tomorrow I'm getting my first DSO. I'm living in an old building with no grounding circuit (230V part of the world). Some of the sockets in my appartment are "zeroed" (have their grounding prongs bridged with Neutral), some don't have GND prongs at all. The socket I intend to connect my DSO to (and the one most of my DUTs will be powered off) is the "no grounding prong" type. Now, I have two options:
  • Install a normal modern socket and then "zero" its GND prong (short it to N)
  • Leave it as it is (essentially "floating" my DSO in the process, right?)

.

What would be your suggestion, guys? Which option is less bad?

Regards,
Zbig

Do the sockets which are "zeroed" actually have a link between the Neutral & GND pins inside them,or do they just look like that if you meter them?
If the latter,you may have a safety ground after all.

If the former,they are  basically useless as a GND if your socket is wired correctly,& very dangerous,if your socket has the Active & Neutral connections transposed.
Don't kid yourself that Electricians don't make mistakes---they do!

Of the two,I would go with the 2 pin unearthed option,as in that case,there is no connection between the metalwork of your instruments & either side of the Mains.
It is,in my opinion,not as safe as as a proper 3 pin socket with a protective Earth.

As Paul has pointed out,many people use the 2 pin non-earthed option without incident.
I do disagree with him when he says it is safer than a  3pin connector with protective Earth connection.
 

duskglow

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Re: Oscilloscope and no proper grounding
« Reply #9 on: July 03, 2013, 05:13:54 am »
Many people do a lot of things out of necessity that are not ideal.  Just this afternoon, I was driving to the surplus place, and someone in a white car was dodging through traffic, tailgating, hitting their brakes repeatedly, weaving around, and finally cut across two lanes of traffic.  He did so without incident and no one got hurt.  The alternative of driving safely would have been much safer, but one could say that many people drive stupidly without incident.  That doesn't mean you want to tell people that it's OK to drive stupidly because everybody does it.

It's a bad example because driving stupidly is a choice, and proper grounding isn't always, but that's how I see it.  Ground if you can, and have a good reason for not doing it.  Don't just do it because you think you can get away with it.... because that's when you won't.
 

Offline IanB

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Re: Oscilloscope and no proper grounding
« Reply #10 on: July 03, 2013, 05:17:31 am »
Paul, there is a difference between an ungrounded toaster and an ungrounded oscilloscope. One connects to external (often faulty) circuits.

There's an even bigger difference. My toaster is fitted with a two conductor power cord and a two pin plug, in common with a vast number of electrical devices in the USA. Since it was designed this way, it is perfectly fine to plug it into a two pin socket. You could not connect it to ground if you wanted to.

However, my oscilloscope, my power supplies and my soldering station are all fitted with a three pin grounded plug, and the ground is connected internally. Since the devices were designed this way with a three pin plug, the ground pin must be connected to a proper mains ground at the supply. That's the difference. You need to use equipment as it was designed to be used. In the USA (and the UK and probably much of Europe) it is forbidden to cut off the ground pin or leave it unconnected if the equipment is fitted with a three pin plug.
I'm not an EE--what am I doing here?
 

Offline Tepe

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Re: Oscilloscope and no proper grounding
« Reply #11 on: July 03, 2013, 09:10:09 am »
Yeah, 'cause it's not.  For all you know neutral could be +80V relative to local earth, then all you s**t gonna zap you when you touch it.  It might even be intermittant just to make it more fun.
Paul Price most likely has TT grounding so that scenario sounds a bit unlikely.
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alm

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Re: Oscilloscope and no proper grounding
« Reply #12 on: July 03, 2013, 10:00:13 am »
If the former,they are  basically useless as a GND if your socket is wired correctly,& very dangerous,if your socket has the Active & Neutral connections transposed.
Don't kid yourself that Electricians don't make mistakes---they do!
I agree. Even if neutral and phase are wired correctly now, an absent-minded electrician (or hobbyist) could accidentally switch them in the future. You wouldn't notice since 99.9% of the modern equipment does not care about polarity (as is evident from the unpolarized plugs used in much of Europe), until you got zapped by touching your scope. If someone switches ground and neutral in a proper three wire grounding scheme, then you'll quickly find out because the GFI (if present) will trip.

Neutral can also get cut. It then acts as a voltage divider of all plugged in equipment with the leakage resistance of the cut cable. This means that its potential will be very close to that of the phase.
 

Offline Paul Price

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Re: Oscilloscope and no proper grounding
« Reply #13 on: July 03, 2013, 10:50:54 am »
My suggestion is to discount anything Duskglow has to say to limit your information on this topic and peruse the two links that I have inserted into my first comment posted here that have a lot of  pro and con information on this subject.

Duskglow has no expert authority to censor my remarks.

Please leave hysterical or censoring comments to bullies, fascists, and some other self-righteous-enabled blogging sites.

« Last Edit: July 03, 2013, 12:09:40 pm by Paul Price »
 

Offline c4757p

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Re: Oscilloscope and no proper grounding
« Reply #14 on: July 03, 2013, 01:45:01 pm »
Your comment suggests that you think experience matters. Why, then, do you disregard all the expert criticism that you receive every time you post on this topic?
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Offline Paul Price

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Re: Oscilloscope and no proper grounding
« Reply #15 on: July 03, 2013, 02:03:57 pm »
My comment suggests that people should examine all available information available on an important safety issue, that there is more than one side to this story, and a plea to all to refrain from self-righteous censoring and hysterical and rude comments.
« Last Edit: July 03, 2013, 02:06:32 pm by Paul Price »
 

Offline madshaman

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Oscilloscope and no proper grounding
« Reply #16 on: July 03, 2013, 02:22:53 pm »
Yeah, 'cause it's not.  For all you know neutral could be +80V relative to local earth, then all you s**t gonna zap you when you touch it.  It might even be intermittant just to make it more fun.
Paul Price most likely has TT grounding so that scenario sounds a bit unlikely.

I'm not so sure it's unlikely, neutral will be connected to remote ground, which could, due to many things have a non-trivial potential vs local ground.

True, if neutral is tied to ground locally then the worst that will happen is that a DC current will run along neutral.  If the current is too large (and I don't remotely claim to know anything about power geberation protection and control ststems) it would probably cause some kind of fault.

So yeah, unlikely a chassis connected locally to both N and local ground will zap you is this situation, but my been shocked many times in my youth side doesn't want to discount "something I didn't think of."  Would rather *not* have to be in a situation where I'm doing forensics to figure out why I got knocked on the floor; interesting though it might be intellectually.

When a crazy man like myself yleans to pragnatism..
To be responsible, but never to let fear stop the imagination.
 

duskglow

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Re: Oscilloscope and no proper grounding
« Reply #17 on: July 03, 2013, 02:26:53 pm »
Paul, I am not censoring your replies.  I have no power to do that.  I am suggesting that they be disregarded.  There is a time to insist on being right.  That time is not when a newbie is asking for advice on a topic that could cause them personal injury if they get it wrong.  I don't care how much experience you claim to have, if you are giving dangerous advice, i will call you out on it.  That is the responsible thing to do.  i will not stand by and watch people be given dangerous advice by someone who should know better.

That said, I acknowledge that you may have a point.  There are circumstances where not grounding is appropriate.  However, to claim that not grounding is *safer* is not responsible, bad advice, those circumstances are not common, and you really need to understand the concept of "not muddying the waters".  For the purposes of this discussion, the correct advice is "yes, you should ground if possible", full stop.  This is not a discussion to get into the subtleties, because it simply muddies the waters and confuses the questioner.

Please stop putting being right over being responsible.  And if a little judicious rudeness gets this point across, so much the better.  I have actually constrained myself, your responses actually anger me a lot more than I'm getting across.  Intentionally putting someone in harm's way for the purposes of ego satiation is one of my triggers.

OP, if you have any doubts at all, please consult an electrician.  This is what they're paid for

EDIT:   I just remembered something I had forgotten.  About ten years ago, I moved back to my hometown of Toledo, Ohio, and the only job I could get was a near minimum wage job at a call center for AT&T@Home.  I was ridiculously overqualified for that job, and the training was boring.  I kept doing pretty much what you're doing, and giving way more information than was needed, just to show that I knew it.  Training was taken over by an ex military guy for a day and he basically told me to shut up.  I caught up with him and expressed my displeasure, and he basically told me that while I was right, it was confusing the issue, and it's really not appropriate to do that.  It's a lesson I haven't forgotten.  Sometimes, even if you know something to be true, the best course of action is to shut up and let things be simple.

Oh, and if I ever give bad or dangerous advice, I *expect* to get called out on it.  That's the responsible thing to do.  I may not like it, but I promise I'll think about it.  Usually I do the right thing.
« Last Edit: July 03, 2013, 02:37:08 pm by duskglow »
 

Offline Paul Price

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Re: Oscilloscope and no proper grounding
« Reply #18 on: July 03, 2013, 02:42:34 pm »
Darkglow, you say, " And if a little judicious rudeness gets this point across, so much the better. "

IMHO, this is a fascist, bullying attitude that is totally sophomoric.

Darkglow, you say, "Sometimes, even if you know something to be true, the best course of action is to shut up and let things be simple." 

I totally disagree, what if the millions of people in Egypt demonstrating today for freedom from oppression took your advice?
« Last Edit: July 03, 2013, 02:47:45 pm by Paul Price »
 

duskglow

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Re: Oscilloscope and no proper grounding
« Reply #19 on: July 03, 2013, 02:48:52 pm »
My nick is duskglow, not darkglow.  Please take the minimum amount of effort to get that right.  If you are intentionally getting it wrong, that's way more sophomoric than anything I've said.

Typically I would just let it slide.  But as I said, your advice is dangerous and not helping.  If that's "fascist, bullying, and sophomoric", I accept that as a risk of protecting a newbie from your irresponsible advice.  If you find it that offensive, please feel free to bring a moderator into the discussion and I will abide by his decision.  But until then, I will continue to call you out, and that's just something you'll have to live with.  I judge the safety of the original poster to be more important than your ego.
 

Offline richcj10

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Re: Oscilloscope and no proper grounding
« Reply #20 on: July 03, 2013, 02:56:41 pm »
In the US, The neutral is tied to ground at the breaker panel in the house. So, They are at the "same potential".
 

duskglow

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Re: Oscilloscope and no proper grounding
« Reply #21 on: July 03, 2013, 02:58:35 pm »
That, of course, assumes that the wiring was installed to code and that there isn't a fault that has disrupted that bonding.
 

Offline richcj10

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Re: Oscilloscope and no proper grounding
« Reply #22 on: July 03, 2013, 03:02:47 pm »
That, of course, assumes that the wiring was installed to code and that there isn't a fault that has disrupted that bonding.

I would agree. That is why, I never plug anything into a outlet that I haven't checked. I carry a outlet wire checker with me at all times.  :-DD
 

duskglow

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Re: Oscilloscope and no proper grounding
« Reply #23 on: July 03, 2013, 03:03:53 pm »
The equivalent of a surgical mask for an engineer. :D
 

Offline edavid

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Re: Oscilloscope and no proper grounding
« Reply #24 on: July 03, 2013, 04:14:06 pm »
In the USA (and the UK and probably much of Europe) it is forbidden to cut off the ground pin or leave it unconnected if the equipment is fitted with a three pin plug.

Not true in the US, at least if you are talking about meeting code.  The ground can be left unconnected if the circuit has a GFCI installed, and the outlet is labeled.
 


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