An oscilloscope with no earth (crappy wiring in house)

[loiphin]

Hi all,

I am an electronics newbie, and have been playing with Arduino circuits for a bit now. I decided to buy a Rigol DSO to hopefully further my education into electronics.

The problem is that my house does not have earthed sockets in most of the house (80's house in Norway.... what were they thinking when they built it???)

So my new Rigol would be plugged in without an earth. I only intend to use the scope for low voltage stuff, ie, less than say 24v.

Would having an unearthed scope pose a problem for my needs? Could I blow anything up in the scope?


Thanks in advance,

loiphin.

[tautech]

If you go forward as you have said, you will be fine.
As you develop greater needs you will need greater knowledge and care to protect yourself and equipment.
Do a "how to use" + your thread name Google search for more info to asses the risks.

[GeorgeOfTheJungle]

If the scope itself ever breaks and develops a leak to ground, then you're at risk... and the differential isn't going to kick in to save you until it's -perhaps- too late. But only *if* the scope *ever* breaks *and* develops a leak to ground. It helps that today's scopes are mostly made of plastics everywhere... but at the BNCs!

But I sometimes have disconnected the scope's earth from ground in order to be able to connect the probes' crocodile anywhere in the circuit... *sometimes* And you still have to watch out because while floating both probes' "grounds" are still tied together, keep it in mind.

[steverino]

In the USA, a GFCI receptacle is used in these situations for personal safety. 

[Thor-Arne]

You really need to get grounding in your lab, both for your own safety and esd dissipation.

Preferably get a certified electrician to fix it, or at least "borrow" some earth ground from a waterpipe or something.

[GeorgeOfTheJungle]

In the USA, a GFCI receptacle is used in these situations for personal safety.

And in Europe -by law- it's mandatory that all mains plugs be protected by a GFCI. If the (faulty) scope's earth were properly grounded the GFCI would kick in inmediately, as soon as you plugged it in or switched it on. But if it weren't, the GFCI wouldn't kick in until you touched it and your body closed the circuit to ground...   

[rob77]

or buy yourself a handheld scope - you don't need to ground it.
i got a Hantek DSO1102B - the performance and features are the same as other DSOs in the same category. it has a built in battery (lasts several hours on battery) and it's powered by a 12V DC plugpack/wallwart. and as a bonus it has a 6000 reading DMM feature (CATIII 600V rated).

[Jeroen3]

or at least "borrow" some earth ground from a waterpipe or something.

Never ever do such a thing unless you are absolutely 100% sure there is a tested path to ground and the GFCI  (RCCB) is working. Plastic tubing is used a lot in buildings these days!
Another major issue while doing that is that any work on plumbing requires your "borrowed" earth to be disconnected. Since the plumber might cut a pipe disconnecting your earth, which might create a "live" pipe.

Another important detail about your non-earthed lab setup is that you must have all your equipment in the same earthed socket-boxes. This way all your equipment grounds are on the same potential.
And be aware of possible the capacitive coupled AC voltage between your probe-ground and project-ground. Always connect probe-ground before powering up your project.

Refer to dave's How Not To Blow Up My Oscilloscope video to understand the issues.

[German_EE]

I don't know the electrical regulations in Norway so the only thing I can suggest is that you spent a little money and get an electrician to inspect your setup.

[mij59]

The problem is that my house does not have earthed sockets in most of the house (80's house in Norway.... what were they thinking when they built it???)

I am not familiar with regulation in Norway, but in the Netherlands it was allowed if the the floor was non conducting.
 

[HackedFridgeMagnet]

http://en.wikipedia.org/wiki/Earthing_system

From memory the reason Norway had the IT earthing system was that it was very hard to get a good earth as there was a lot of non conductive rock underneath.
Remember different places have different earthing systems so some of the info posted before would not apply to an IT earthing system.
Basically there is not as much chance of an earth fault so it is not much of a worry as it is in some places.

I am not familiar with regulation in Norway, but in the Netherlands it was allowed if the the floor was non conducting.

I don't know the electrical regulations in Norway so the only thing I can suggest is that you spent a little money and get an electrician to inspect your setup.

Those sound like good advice.


BTW: Australia, NZ have a modified TN-C-S system which we call the MEN system (Multiple Earthed Neutral, I think the multiple is the ground stake and the water pipe bond).

[ovnr]

Well, you may have a ground somewhere in the house - even 80s houses had grounded outlets (kitchen stove, bathroom, etc). Consider just running a loose ground lead (of suitable size) to your lab - that's what I ended up doing.

Also, you can buy plug-in GFCIs - here's one. If you can't afford to have your house re-wired, I'd strongly suggest buying one for your lab.

(As others already have, I strongly suggest getting your wiring sorted out. Yes, it's ridiculously expensive, but it's worth it. And no more old decrepit outlets and light switches!)

[mij59]

BTW: Australia, NZ have a modified TN-C-S system which we call the MEN system (Multiple Earthed Neutral, I think the multiple is the ground stake and the water pipe bond).
[/quote]

TN-C-S, PEN conductor in the distibution panel split in neutral and ground, see wiki
http://en.wikipedia.org/wiki/Earthing_system

Multiple ground means that the PEN conductor is earthed in different locations ( outside the the building )

[queennikki1972]

I have the same issue. House built in 1947. No ground wires in the walls. In the United States having a electrician redo the wires is crazy expensive and i simply cannot afford it. I have grounding STUDS on my power strips and all my chasis ground although (open ground) are all tied together as they share the same outlets and power strips. I had considered running a ground wire from the ground studs to a grounding rod, but my knowledge of how this affects a 2 wire system is limited. I am confident as far as changing outlets and i do have GFCI outlets. I have search all over Google and have not found a direct answer to my problem other than simply rewiring the house and/or possibly using a Differential Probes or Active Probes. Any input is appreciated.

Fort Worth, Texas USA
 120vac
Main Panel is Grounded.
No ground wire in walls.

Thanks Nikki

[HackedFridgeMagnet]

BTW: Australia, NZ have a modified TN-C-S system which we call the MEN system (Multiple Earthed Neutral, I think the multiple is the ground stake and the water pipe bond).


TN-C-S, PEN conductor in the distibution panel split in neutral and ground, see wiki
http://en.wikipedia.org/wiki/Earthing_system

Multiple ground means that the PEN conductor is earthed in different locations ( outside the the building )

No the Multiple in MEN is not the water bond. That much I can say.

I think the multiple is only in the case of several buildings on one supply.
There is only one Earth and Neutral bond per building ever. 

The first building has the incoming PEN conductor which is split to form Earth and Neutral.
any subsequent buildings on the property can either have

• an Earth cable from the first building run to it. 
• or if the dont have an Earth cable run then  they can bond the buildings local Earth to the incoming Neutral.

Also the Earth Terminal block at any Distribution board may have any number of connections to physical earth, and should definitely be bonded to any metal water pipe.

edit: sry didn't realise I was responding to such an old post 

[HackedFridgeMagnet]

Could an electrician rewire just one outlet to have a properly connected Earth? Then you could use that for your lab equipment.
I'm not familiar with US style split supply, or 6 phase or whatever it is, but, it could be a worry if your ground clip on your probe gets connected to some unsafe voltage. Then your whole lab will be made unsafe.

[FriedMule]

Greetings from Denmark:-) I think that you have 3 sollutions:
as ovnr writes about

Well, you may have a ground somewhere in the house - even 80s houses had grounded outlets (kitchen stove, bathroom, etc). Consider just running a loose ground lead (of suitable size) to your lab - that's what I ended up doing.

Also, you can buy plug-in GFCIs - here's one. If you can't afford to have your house re-wired, I'd strongly suggest buying one for your lab.

(As others already have, I strongly suggest getting your wiring sorted out. Yes, it's ridiculously expensive, but it's worth it. And no more old decrepit outlets and light switches!)

The HPFI or CFCI as it is also called do protect you perfectly, if you should be extremely unlucky you will get a short zap and that's it.
You can also as ovnr says, find an outlet with ground, put a wire in it and then run it all the way to your lab, try to look in your lamp in the ceiling, they do often have a ground because it was more easy just to make ground everywhere.
Last get a Earth rod and make your own ground.

But have you considered if it may not be to your advantage, not to have ground? Your whole system is right now floating and you avoid many of the danger to your gear that a ground do give you.

[AVGresponding]

Greetings from Denmark:-) I think that you have 3 sollutions:
as ovnr writes about

Well, you may have a ground somewhere in the house - even 80s houses had grounded outlets (kitchen stove, bathroom, etc). Consider just running a loose ground lead (of suitable size) to your lab - that's what I ended up doing.

Also, you can buy plug-in GFCIs - here's one. If you can't afford to have your house re-wired, I'd strongly suggest buying one for your lab.

(As others already have, I strongly suggest getting your wiring sorted out. Yes, it's ridiculously expensive, but it's worth it. And no more old decrepit outlets and light switches!)

The HPFI or CFCI as it is also called do protect you perfectly, if you should be extremely unlucky you will get a short zap and that's it.
You can also as ovnr says, find an outlet with ground, put a wire in it and then run it all the way to your lab, try to look in your lamp in the ceiling, they do often have a ground because it was more easy just to make ground everywhere.
Last get a Earth rod and make your own ground.

But have you considered if it may not be to your advantage, not to have ground? Your whole system is right now floating and you avoid many of the danger to your gear that a ground do give you.

This so called 'floating ground' may only serve to provide a false sense of security; while you hold a probe in this system, you run the chance of becoming the path for current to ground...

I've seen a lot of argument in these forums about the relative merits of floating vs earth ground reference, but the fact remains that if you're mucking around with high potential systems there's always going to be a chance for you to be the link between +/-V and GND. Whether your system is isolated or not, that's going to spoil your day (or maybe make it, I hear some people enjoy electric shocks *looks at Big Clive*) and maybe your test gear too. With enough energy in the system it's maybe fatally problematic.

The long and short of it is, if you don't know what you're doing, don't do it. For those that insist on doing it anyway, take every available precaution (RCD/GFCI + isolation tranny + variac + differential probe) but don't expect these things to save your life/equipment if you fuck up badly enough.

There are ways to achieve gear-safe measuring without recourse to all these methods, but they are ONLY for people that understand WHAT THEY ARE DOING and also THE RISKS involved to their person.

@queennikki1972  since you say your main board is grounded (presumably you mean with earth as the reference), there are a few ideas for you to consider.
If your house has drywall/studwall and not stone/brick walls, it might be practical for you to have just one circuit rewired to include a CPC (circuit protective conductor) aka PE (protective earth) for a relatively low cost.
Alternatively, it might be possible to have a radial socket installed directly from the board, perhaps directly adjacent to the board, which you could use with an extension lead to wherever it's needed.

I've seen a few people post that GFCI/RCDs will work fine on a 2 wire system. In theory, maybe, but I'd not trust my life to it.


Ultimately there are NO safe ways to manually probe unsafe voltages, there are only ways to reduce your risk of death/serious injury.
If you make yourself the current path for a large voltage, GFCI/RCDs and isolation transformers will only limit the maximum V/I you're exposed to, they won't make it 'safe'.

I hate when people say 'as an engineer or w/e with X qualifications and Y years experience I can tell you Z', but in this instance I'll break my own rules a bit lol...
As a mechanical and electrical engineer and electronics hobbyist of 40 years experience, with C&G and HNC qualifications, I can tell you I've had an actual mains V electric shock just ONCE (about a year ago, hell of a time to lose my virginity dammit), due entirely to the fact that electricity rightly scares the shit out of me, and therefore I am SUPER careful where I stick my probes (and also my fingers, now).

[janoc]

In the USA, a GFCI receptacle is used in these situations for personal safety.

And in Europe -by law- it's mandatory that all mains plugs be protected by a GFCI. ...

Ehm, nope. This varies between countries (building and electrical codes are not standardized across Europe!) and especially the older installations predating the rule (if there is one) don't need to be upgraded to match the newer code unless major work is being done that requires a new approval.

So if you are relying on this you will sooner or later get a very nasty surprise.

[Mr. Scram]

Why did we dig up a thread from 2014? Especially one which has two or three currently active duplicates with what’s essentially the same question.

[AVGresponding]

Perhaps the mods should merge the threads

[pcmad]

you can get ground from metal water pipes  i you house

[Mr. Scram]

you can get ground from metal water pipes  i you house

We really need a few FAQs including one why water pipes are not a good replacement for ground. 

[Jeroen3]

Yes, this faq needs to get there. Also adding that typical mains filter leakage current is not faulty.