Mains sockets with no earth

[JohnnyMalaria]

I should probably have said that I originally come from the UK

"Mains sockets" and "earth" gave you away

[Monkeh]

On the RCD front, I always thought that they were to guard against earth faults... so I don't understand how they can work without a reference to earth.

They are to protect against current returning to its source (the side of the transformer winding connected to neutral) via a path other than the neutral. Said winding is also connected to earth, and returning via the earth conductor or the greater mass of earth is called an 'earth fault'. They need no reference to this - they measure the difference in current between the line and neutral conductors. Any difference must be returning via an alternate path.

I should probably have said that I originally come from the UK

"Mains sockets" and "earth" gave you away

At least he didn't call them plug sockets..

[james_s]

The UK uses a ring circuit for the most part since it allows a narrower gauge of wire to be used for a given power requirement. Radial/spur/star is less common

slowly the uk is moving away from ring finals,more and more sparks  ,mainly the younger ones or those new to the trade ,dont like em and would rather struggle getting 2 larger conductors into a terminal,there fear is of the cable being overloaded if one leg is broken,which whilst true,the chance of a broken wire happening without somebody fiddling were they shouldn't or a badly installed installation are fairly low

I have mixed thoughts on the ringmain concept. It has clear advantages, although the concerns you mention are valid. Lots of things are ok *IF* properly installed and nobody has mucked with them but that's a big IF, especially in older houses where the likelihood of somebody having messed with something only increases with time. On the other hand it's not like those concerns apply only to a ringmain, over here we have these stupid spring loaded backstab terminals on receptacles and switches, or rather on the cheap hardware sold for domestic use, commercial "spec grade" and hospital grade forbids them. I've had problems on several occasions with those, once in my own house and several I fixed for other people, one that very, very nearly set the house on fire. I can only wonder how many house fires of indeterminate and "electrical" cause have originated with those. The annoying arc fault breakers the NEC mandates now for new construction are a band-aid over the problem, the tradesmen love those push-in terminals because they're so quick and easy to install but I bet most don't use them in their own house.

[vk6zgo]

if you dont have an earth your rcd will not work.were does the fault current go as there is no path for it to travel.

GFI does not depend on having an earth connection, nor does it care what the path is for current to travel outside of the two wires it monitors.  If a current is flowing through you, then that amount of current will be missing from the return current in the neutral.  GFI sees the imbalance and trips.

Yes, another name for such devices is "core balance relay".
If the current flow in the L & N lines is equal, the relay is "balanced" & does not operate.
If the currents are not equal, the relay operates, opening the circuit for both L & N.

[Ed.Kloonk]

whilst the rcd dosnt have an earth connection it still relies on the circuit somewhere being connected to earth,otherwise theirs nowhere for the imbalance current to flow.If the experiment mentioned above is to scary try putting an rcd on the secondary of an isolating transformer and connect the output to earth ,what happens?

True, in a truly isolated system the RCD won't trip because there is no fault current.  But since there's no fault current, there's no shock and nothing to protect from.

If you somehow manage to connect your arms/hands to either terminal, even a portion of any isolated mains will do you in. All it takes is enough to fibrillate the heart. However, if the supply is earth bonded and protected with a RCD, chances are much higher that you wont be sitting there becoming burnt toast.

[Brumby]

Yes, another name for such devices is "core balance relay".

Now you're showing your age..... 

[tooki]

Sure it will

so if we don't need an earth why don't we use an rcd on the secondary of an isolating transformer?after all thats  a circuit without an earth

Neutral is tied to earth somewhere in the domestic wiring system of every developed nation as far as I'm aware

not on the consumers side,otherwise your rcd/gfi would be permanently tripped

Uhhhh… what? No. The RCD isn't looking at what's happening upstream of it (i.e. in the power grid). It simply has inputs and outputs for the L and N, and if the current that flows in isn't the same as what flows out, it trips. If N and PE are tied together at the consumer unit, that's still upstream of the RCD, and thus irrelevant to it.

In fact, RCDs are used when it's impractical to add an actual protective earth conductor, precisely because they do add protection when earth is missing.

[themadhippy]

the post that started it all

You still have RCD protection without an earth.

without  earth  there is no return path so  would the experts like to explain how a current can flow in what is effectively an open circuit

If N and PE are tied together at the consumer unit

i meant the consumers side,or output, of the rcd

precisely because they do add protection when earth is missing

again i ask,if earth is missing how does a fault current flow?

[bdunham7]

without  earth  there is no return path so  would the experts like to explain how a current can flow in what is effectively an open circuit

If there truly is no ground reference for both the voltage and your feet, indeed no current will flow and the RCD will not trip.  But it doesn't need to--because there's no fault current to worry about.  The RCD is still standing by for any faults that develop that result in current flowing through you other than those that result from you touching both sides of the power.

[Monkeh]

the post that started it all

You still have RCD protection without an earth.

without  earth  there is no return path so  would the experts like to explain how a current can flow in what is effectively an open circuit

If N and PE are tied together at the consumer unit

i meant the consumers side,or output, of the rcd

precisely because they do add protection when earth is missing

again i ask,if earth is missing how does a fault current flow?

Are we accidentally equating earth with the CPC?

The neutral, sort of by definition of being neutral, is connected to earth (the 'greater mass of earth', the soil under your feet). You do not need an earth wire in an installation for current to flow via the literal earth.

[Someone]

So, it sounds to me as though I should install some three-pin sockets (US style), on extension cords, with the earth connectors disconnected from each other - that would produce the same effect as cutting off the three-pin plugs and putting on two-pin plugs. Then I need to stop worrying about the absence of an earth connector?

No, equipment that has a mains earth pin usually relies on it for safety and/or EMC. Removing that connection is a very very bad idea.

If you don't understand the standards/requirements (which is plainly obvious from your posts so far) then suck it up and hire a professional to do the job. Just ask an electrician to put modern grounded points everywhere and its done.

[jmelson]

On the RCD front, I always thought that they were to guard against earth faults... so I don't understand how they can work without a reference to earth.

They compare current on line and neutral.  If the current is the same, the devices must be OK, all current flows out one outlet prong and back on the other.  If the currents DO NOT match, then the current MUST be flowing out of the device somewhere, and typically that would be through a person's body.
The comparison is done by passing both L and N wires through a ferrite core.  Only equal and opposite currents cancel out.

Japan generally has no ground pin on any residential sockets, but they do in industrial and lab settings.

Jon

[michael@metgen.tech]

So, it sounds to me as though I should install some three-pin sockets (US style), on extension cords, with the earth connectors disconnected from each other - that would produce the same effect as cutting off the three-pin plugs and putting on two-pin plugs. Then I need to stop worrying about the absence of an earth connector?

No, equipment that has a mains earth pin usually relies on it for safety and/or EMC. Removing that connection is a very very bad idea.

If you don't understand the standards/requirements (which is plainly obvious from your posts so far) then suck it up and hire a professional to do the job. Just ask an electrician to put modern grounded points everywhere and its done.

Your comment doesn't really make sense - obviously not coming at this from a Japan perspective.

The standard in Japan is to NOT have any earthing. There are no "modern grounded points". The problem I have is that I have equipment that is not Japanese, has earth connectors and, for some, an uninsulated metal case. So "hiring a professional" won't change anything. I am trying to better understand of the risks that I am actually exposed to by following the local standards and if there are any workable mitigations.


Mike

[michael@metgen.tech]

On the RCD front, I always thought that they were to guard against earth faults... so I don't understand how they can work without a reference to earth.

They compare current on line and neutral.  If the current is the same, the devices must be OK, all current flows out one outlet prong and back on the other.  If the currents DO NOT match, then the current MUST be flowing out of the device somewhere, and typically that would be through a person's body.
The comparison is done by passing both L and N wires through a ferrite core.  Only equal and opposite currents cancel out.

Thanks. Obvious now that I look at the insides of one.

Japan generally has no ground pin on any residential sockets, but they do in industrial and lab settings.

My experience too.

Thanks,

Mike

[Zero999]

It's true that RCDs will work, if the appliance lacks an earth connection, but an earth is required at the supply side. RCDs need the mains supply to be earth referenced, so they won't work if the entire circuit lacks an earth connection. Try connecting an RCD to the secondary of an isolation transformer and note that it won't trip, if either conductor is connected to earth.

[nctnico]

You still have RCD protection without an earth.

if you dont have an earth your rcd will not work.were does the fault current go as there is no path for it to travel.Dont believe me then remove your main incoming earth and  bonding and  short earth to live or neutral somewhere on the consumers side and see how long it takes for the rcd to trip

In that case you don't have a problem. If there is no ground the current can flow into then you can't get a shock!

It's true that RCDs will work, if the appliance lacks an earth connection, but an earth is required at the supply side. RCDs need the mains supply to be earth referenced,

Almost right. RCDs need the neutral to be earth referenced at the primary side. But after that you don't need earth in the installation. It is assumed the building is somehow grounded (and in 'wet' rooms like the bath room it is often mandatory to ground the floor and every metal object).

[Someone]

So, it sounds to me as though I should install some three-pin sockets (US style), on extension cords, with the earth connectors disconnected from each other - that would produce the same effect as cutting off the three-pin plugs and putting on two-pin plugs. Then I need to stop worrying about the absence of an earth connector?

No, equipment that has a mains earth pin usually relies on it for safety and/or EMC. Removing that connection is a very very bad idea.

If you don't understand the standards/requirements (which is plainly obvious from your posts so far) then suck it up and hire a professional to do the job. Just ask an electrician to put modern grounded points everywhere and its done.

Your comment doesn't really make sense - obviously not coming at this from a Japan perspective.

The standard in Japan is to NOT have any earthing. There are no "modern grounded points". The problem I have is that I have equipment that is not Japanese, has earth connectors and, for some, an uninsulated metal case. So "hiring a professional" won't change anything. I am trying to better understand of the risks that I am actually exposed to by following the local standards and if there are any workable mitigations.

https://ja.wikipedia.org/wiki/%E9%85%8D%E7%B7%9A%E7%94%A8%E5%B7%AE%E8%BE%BC%E6%8E%A5%E7%B6%9A%E5%99%A8

the 2005 revision of Extension Regulations 3202-3 In new homes, etc., it is recommended that all outlets in the home be equipped with a grounding electrode regardless of the usage phase

So yeah, there is that whole its the recommended way to do it thing, in your specific country, according to their specific standards. Some of us have do have a solid international view.

[Zero999]

It's true that RCDs will work, if the appliance lacks an earth connection, but an earth is required at the supply side. RCDs need the mains supply to be earth referenced,

Almost right. RCDs need the neutral to be earth referenced at the primary side. But after that you don't need earth in the installation.

That's what I said. Read it again.

[michael@metgen.tech]

https://ja.wikipedia.org/wiki/%E9%85%8D%E7%B7%9A%E7%94%A8%E5%B7%AE%E8%BE%BC%E6%8E%A5%E7%B6%9A%E5%99%A8

Excellent, I had not found that, thank you. The only issue with my new place is that it was built in 2002 - pre the 2005 changes. Also, unless you have lived here, you would find it hard to believe how tradesmen, and anyone else for that matter, apply regulation. Dealing with them generally feels like pushing a ball up hill with a piece of wet spaghetti!

It turns out that I may have to have new cables run for an electric oven. If so I can ask the electrician to run an earth wire as well.

I presume that with a 200V supply the Earth is at the mid point?

[bdunham7]

If you somehow manage to connect your arms/hands to either terminal, even a portion of any isolated mains will do you in. All it takes is enough to fibrillate the heart. However, if the supply is earth bonded and protected with a RCD, chances are much higher that you wont be sitting there becoming burnt toast.

This has been raised before in discussions about isolation transformers.  Yes, if you grab both sides, you get buzzed.  And if you grab both sides of an earth-referenced RCD/GFI protected circuit, you still get buzzed but if your feet are sufficiently grounded so that additional current also goes to ground through your toes, you might get lucky and have the power shut off.  This is why although I advocate the proper use of isolation transformers, I don't advocate using them in a general 'safety zone' sort of way. 

However, the point remains that no ground is needed for RDC/GFI, although they are a bit pointless if the power source is truly isolated and remains that way with no faults.  You can dream up corner case scenarios even for ground-referenced power.  Imagine grabbing both sides of a split-phase system with both hands and bare feet on concrete.  The leakage to ground may be balance out and thus the GFI won't trip. 

[james_s]

A GFCI is a lot like a seatbelt. It's there to provide some protection in the event that you end up in a really bad situation where you are the most convenient path to ground. It's not there to enable one to be careless with electricity, if you touch a GFCI protected circuit you will probably still get a shock, but hopefully the power will cut quickly enough that it won't be lethal.