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Lab with NO grd, what about gear?
Posted by
FriedMule
on 15 Sep, 2018 00:05
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In Denmark, where I live, it is common to have outlets with no ground / earthing.
What does that mean for a electronic lab?
Meaning oscilloscope, psu, dmm, anstatic mat and yes, it all?
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#1 Reply
Posted by
ArthurDent
on 15 Sep, 2018 03:46
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I live in the U.S. but as I understand it from the following video, there are both grounded and ungrounded outlets available in Denmark for home use but if anyone was wiring a lab or any commercial business they would make sure that all the equipment had ground equipped power cords to plug into ground equipped outlets.
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#2 Reply
Posted by
t1d
on 15 Sep, 2018 04:07
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I think you are going to need the earth ground, rather quickly... Not just for safety, but for dual (positive and negative voltages) circuit designs.
It is not particularly difficult, or expensive, to add an earth ground, for your lab. In the USA, in my part of the country, the earth ground is simply a long, heavy, copper (or galvanized metal) rod, driven into the ground. A heavy gauge wire is clamped to this rod and it goes into the house, to make the needed connections.
https://www.lowes.com/search?searchTerm=grounding+rod
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#3 Reply
Posted by
Ian.M
on 15 Sep, 2018 07:43
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Not quite. The presence or absence of a true Earth ground doesn't affect the ability of a PSU to provide positive and negative rails to a circuit - if it did hand-held electronics that used split supplies would be impossible!
However, modern test equipment with SMPSUs, designed to operate with a grounded supply is *UNSAFE* to use without a ground connection, and the risk significantly increases if multiple items have their ground connections tied together, but not grounded, as the permitted leakage currents to ground in their line filters can add up to a dangerous current which will cause any supposedly grounded exposed metalwork to be a serious shock risk.
You either need a proper ground, or equipotential bonding for the whole bench area. How to do that safely and legally depends on your existing electrical installation and your local electrical regulations, so if in doubt, consult a local electrician.
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#4 Reply
Posted by
0xdeadbeef
on 15 Sep, 2018 08:12
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Actually what is called "ground" connector here is the protective earthing (PE) conductor. It's not needed for functionality (as the two other connector are phase and neutral) but "only" for safety. Like devices with exposed metal parts usually need this kind of connector so the metal case etc. is connected to the protective earthing conductor to make sure that even in case of a catastrophic short circuit inside the device, touching the metal parts won't be fatal. Devices without any exposed metal parts can use the "Euro" plug which doesn't feature the PE conductor. There are several safety classes and all but in a nutshell it's about exposed metal parts.
So connecting equipment which would need a PE conductor to a Euro plug socket without one is a safety hazard, not so much a functional problem. Of course, stuff like an ESD mat also needs to be grounded (and you'd usually use PE for this) but there you could also use a water faucet or whatever.
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#5 Reply
Posted by
FriedMule
on 14 Oct, 2018 07:17
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About safety: In Denmark the circuit breaker trips if there are any different in the power between phase and neutral so if you touch a metal case, it will trip in a tiny fraction of a second.
I am thinking that so many talks about galvanic isulation of the test gear, avoiding grounding anything and so on, but the other hand I do also hear about gear not working correct if not grounded propperly?
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#6 Reply
Posted by
Kleinstein
on 14 Oct, 2018 07:27
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Normally modern gear should work without the ground connection. However there is the mentioned leakage current problem and also a possible EMI problem. So especially with many instruments connected this can be a problem.
If you are Lucky it is only the cheaper outlets without the ground. The wiring could be still have ground. At least in Germany one hardly gets 2 wire cables for installation and they tend to be more expensive than the 3 strand ones. So best have an electrician check the wiring.
The Danish plug looks a lot like a
.
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#7 Reply
Posted by
IanB
on 14 Oct, 2018 07:36
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About safety: In Denmark the circuit breaker trips if there are any different in the power between phase and neutral so if you touch a metal case, it will trip in a tiny fraction of a second.
I am thinking that so many talks about galvanic isulation of the test gear, avoiding grounding anything and so on, but the other hand I do also hear about gear not working correct if not grounded propperly?
The ground may be used to avoid stray voltages, "floating" voltages, and for interference suppression. Even though it may not be required for human safety, there are other electrical reasons for having it.
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#8 Reply
Posted by
FriedMule
on 14 Oct, 2018 08:09
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I live in a rented apartment from 1972 and I do not think that there is ground in most of my outlets.
What is your advice, how would you do?
I have a heater but do not know if it is connected to ground.
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#9 Reply
Posted by
bd139
on 14 Oct, 2018 08:38
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I know nothing about Denmark mains but is it possible your neutral is grounded?
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#10 Reply
Posted by
FriedMule
on 14 Oct, 2018 10:20
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Great question, I'll try to find out.
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#11 Reply
Posted by
station240
on 14 Oct, 2018 10:35
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Do you have any exposed metal water pipes you could clamp an earth wire to ?
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#12 Reply
Posted by
HB9EVI
on 14 Oct, 2018 11:09
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As it was common in the 70' in many european countries, there wasn't installed a separate PE wire to the outlets; installation type was TN-C where the PE pin in the sockets was bound to the N.
Our house dates from the same time and had this type of installation, what made the usage of an RCD impossible - but was my personal requirement. So transferred to whole installation from TN-C/TN-C-S hybrid to all TN-S, what means to add a PE to every outlet; it was quite a work, but it's worth it.
Since you're renting your flat, and you have no PE pin in your outlets, my advice would be installing an outlet with a PE pin and wire it to N - that's still better than running the devices with floating PE. But before, you have to assure that the house installation is a TN-system
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#13 Reply
Posted by
0xdeadbeef
on 14 Oct, 2018 11:28
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Dunno about Switzerland, but in Germany TN-S (separate PE) is mandatory for new buildings since 1973. And using TN-C (neutral used as PE) in older buildings is only allowed for a diameter of 10mm² (copper) or 16mm² (aluminium).
Again, this is all about safety. Using a device designed for an IEC connector on an outlet without or with lacking PE involves risk of death in case of a failure of this device.
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#14 Reply
Posted by
HB9EVI
on 14 Oct, 2018 11:49
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Good to know; it seems they slept here, since our house dates from 1974 and all outlets were wired as TN-C, while the installation itself is a TN-C-S with a separed earth rod connected to the PEN
Back to the topic; I read this here:
In Denmark the high voltage regulation (Stærkstrømsbekendtgørelsen) and Malaysia the Electricity Ordinance 1994 states that all consumers must use TT earthing, though in rare cases TN-C-S may be allowed (used in the same manner as in the United States). Rules are different when it comes to larger companies.
This means, you have to add a PE-wire from the house installation to your outlet in the lab; hooking the N to the PE pin in the outlet IS NOT ALLOWED!
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#15 Reply
Posted by
exe
on 14 Oct, 2018 15:43
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Do you have any exposed metal water pipes you could clamp an earth wire to ?
Oh shi~, don't do it. Unless you want to electrocute somebody taking bathroom or something. Not to mention you don't know if part of the pipe was replaced with a plastic one.
I think some idiots did it in my previous appartment. Touching radiator was painful.
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#16 Reply
Posted by
Brumby
on 14 Oct, 2018 16:34
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Do you have any exposed metal water pipes you could clamp an earth wire to ?
You don't do that here any more - and it would be risky to suggest that, IMHO.
Doing so relies on there being very good and reliable earthing of the pipes all the way from the connection point to the soil in which they are embedded. It only takes some dry dirt around a pipe or one gap in the electrical conductivity to send current in a direction that you don't want.
There is also the very real risk that someone working on a pipe somewhere up the line could find themselves between a fault current and the path it wants to take. This is no joke - I have seen plumbers with a meter connected across a pipe that needs to be separated for whatever reason and if it measures a voltage above a certain limit, then they have to walk away from the job and get someone in to sort it out.
Separate earth stake is really the only safe way - which is a problem in units/apartments.
Unless you want to electrocute somebody taking bathroom or something. Not to mention you don't know if part of the pipe was replaced with a plastic one.
Exactly
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#17 Reply
Posted by
FriedMule
on 14 Oct, 2018 17:43
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You are all great, thank you!
I have found out that we use something called "TT systemet" does that mean anything to you?
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#18 Reply
Posted by
helius
on 14 Oct, 2018 17:51
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TT stands for "Terra-Terra", and is the system where each premises is independently grounded (through a copper rod driven into the earth). The electric service connection does not contain a ground conductor, and the protective earth pins in the outlet sockets do not connect back to the power feed, only to the local ground rod.
https://en.wikipedia.org/wiki/Earthing_system#TT_networkThe TT system has high ground fault impedance (since the earth between the local building and the utility transformer is part of the loop). That means that in the case of an insulation fault from phase to chassis in equipment,
even if the equipment has a grounded plug, the fault current may be too low to trip a breaker. The RCD is what provides safety in this scenario.
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#19 Reply
Posted by
Ian.M
on 14 Oct, 2018 18:24
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If you cant run an adequate ground connector to a ground rod for a TT system because you are on a high floor in an apartment building etc. its possible to use a large isolating transformer (so the whole bench can be powered through it), then on the secondary side, set up an equipotential bonding zone for supply ground, with secondary side neutral tied to it, followed by a RCD. Any fault currents are local to the bonding zone, so cannot cause the safety problem with unexpected potentials across any insulating joints or section in water pipes etc. I must emphasise that *ALL* equipment that is on the bench or connected to it *MUST* be supplied by the same isolating method to avoid endangering plumbers etc.
N.B. This arrangement almost certainly doesn't meet local electrical code for a fixed installation, so only build it as a plug-in setup.
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#20 Reply
Posted by
FriedMule
on 15 Oct, 2018 11:04
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Since that all gear do not get grounded, why isolate more by using a isolation transformer?
Would it not be enough if I connected all the gear to the same outlet?
By the way, there are no ground rod at all and we have properly te stupdst "safety"! It is posible to put the plug in the socket in two ways, so there about no way to know if phase or neutral is getting the letal power!
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#21 Reply
Posted by
lypse
on 15 Oct, 2018 11:32
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Hi FriedMule,
If you cannot use some pipework for the PE connection, consider using a handheld oscilloscope (isolated channels) and skip the anti static mat.. in short, eliminate ways you could shock yourself?
/Alex
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#22 Reply
Posted by
0xdeadbeef
on 15 Oct, 2018 11:34
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By the way, there are no ground rod at all and we have properly te stupdst "safety"! It is posible to put the plug in the socket in two ways, so there about no way to know if phase or neutral is getting the letal power!
IMHO that's not a safety concern. It's better to always expect voltage on both, line and neutral. In countries were neutral and line have a specific position on the plug/socket, the installation can still be screwed up and you die on the assumption it wasn't.
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#23 Reply
Posted by
Ian.M
on 15 Oct, 2018 11:48
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The isolation transformer controls where the ground leakage currents and any ground fault currents return to, so its necessary if you can't put in an adequate grounding conductor and ground rod(s) for a TT system. It also doesn't care which way round Line and Neutral are on its primary or even if the primary is fed between two phases of a three phase supply as long as the voltage is correct, and if wired as described will provide a clear Neutral on the secondary side. N.B if wired as described it doesn't provide any 'isolation' for working on equipment, its output should be treated with the same respect as any other mains supply.
Due to its surface resistivity and the 1 Meg resistor in its grounding lead, an antistatic mat is not a shock hazard. However in the absence of a proper ground, you need an equipotential bonding zone, so there is a path for charge equalisation, or even for charge to leak away to true ground via a higher impedance path than would be acceptable for safety grounding if the equipotental bond ties in water pipes, rebar or other structural metalwork.
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#24 Reply
Posted by
FriedMule
on 15 Oct, 2018 19:05
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