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Hi there C-H, and welcome to ECN! Nice to get another member from Europe.

I think I see the point you're making about using class I equipment fitted with a Schuko plug in an old non-grounding receptacle, but I'm not sure I like the idea.

The rules here in England are more along the lines that class I equipment is designed to be connected to an earth and therefore should only be connected to a grounding receptacle, regardless of whether or not there is any other earthed metalwork in the room.

That's not to say that in the days when two-pin non-grounding outlets were common thgat people didn't wire class I equipment to a 2-prong plug and just leave the ground wire floating.

> Ok, correct me if I'm wrong: hooking up
> a class 0 device to a Schuko receptacle
> is dangerous because it creates
> a false feeling of safety?

No. It is dangerous because a class 0 device has a metal casing which is not connected to earth. It also only has a single layer of insulation. If this insulation is damaged, the casing will become condutive. In case you are touching only this, it will only deliver a shock. But, if you are at the same time touching an earthed object, the shock will be lethal. Unearthed sockets and class 0 devices should only be used where this cannot happen. (Non-conductive environments)

Class 0 appliances used in an earthed environment should be converted to class I (i.e. earthed), or Class II (be made double insulated) or simply scrapped.

There is a simple way of safely using them "as is". An RCD protected extension lead with a few unearthed sockets. However, this is rarely used in practice.

There is also a more expensive way: An insulating transformer, i.e. a 230-230V transformer, with separate primary and secondary windings. Since there is no connection to earth on the secondary side, a live to earth-fault can never occur. Shaver sockets are often designed this way.

Britain has choosen the other way: Earth everything. All plugs are three pin, which means that anything with a metal casing should be connected to earth. This is safer than the German approach and has therefore been adopted as the international standard. Most, if not all, industrialised countries require sockets to be earthed these days.

But the metal casing of a class 0 appliance will not be earthed regardless of whether it is connected to either a Schuko outlet or a non-grounding receptacle. If connected to a Schuko outlet the grounding contacts in the rceptacle simply don't connect to anything.

The argument over class 0 appliances seems to be more about whether there is any other earthed metalwork nearby.

Or are you saying that class 0 appliances should not be used where Schuko outlets are installed because there could be a class I appliances (with grounded frame) operating within reach of the class 0 unit?

Yes, exactly!

O.K., I see the theory behind what you are saying, but I don't understand how it can work in practice.

The average person doesn't know that there are class 0, class I, and class II appliances, much less understand or care about the differences.

All he knows is whether the plug on the end of the cord fits the outlet so that he can use the appliance. If the plug fits and it works, he will assume that all is well.

For so long as class 0 devices remain in service, surely the only way (practically speaking) to prevent somebody using a class I appliance with a grounded case nearby is to not install any Schuko receptacles but revert to having all non-grounding outlets.

You're right: It doesn't. It was a bad idea from start.

The UK way is much better. (But I don't like the fused plugs and the ring mains...)


Yup. But when it doesn't fit, he or she will make it fit. Our Austrian friend has already presented a number of ways...

[This message has been edited by C-H (edited 09-22-2002).]

Hmm, I guess it serves as a reminder that what sounds good in theory sometimes just doesn't work out in practice.

I have to agree with you there. The concept of a fused plug is fine, but our 13A (BS1363) plugs are just so big and bulky.

I don't like the ring circuits as used in this country either, and I believe it's time they were abandoned. Any reasons given for their adoption in the 1940s are really no longer valid, if indeed they ever were.

It you search back through the ECN archives you find several threads about U.K. ring circuits.

I can imagine that the situation was very different 50 years back: The flexible cables were of rubber or cloth and wore out rather soon causing short circuits. I suspect silk or whatever they used also caught fire rather easily, so fused plugs were probably a great idea. Once they had come up with the idea of a fused plug, they took it one step further and put a big 30A fuse in the fusebox.

But, has anyone had a modern plastic cord that short circuited? (Apart from those used for irons) What are the odds that the cable to my telly will become damaged enough to cause a short? And that it catch fire if it does short?

In older houses in Austria it's typical to have one or 2 Schuko receptacles per room and the other ones ungrounded. I usually kepp it this way when changing anythin, both for th possibility of plugging in old devices without altering them and the oldfashioned look. I also prefer toggle switches (obsolete since the mid-1960ies) for the look and feel. Some that were rarely used are still in perfect shape, otherwise the spring goes bad and they don't move any more.
BTW, does anyone know when the new european color coding has come into use and replaced the old black/grey/red scheme?

Interesting point about the cords, and not one I thought about that closely. By the time the ring circuit really became fully accepted here in the 1950s, PVC-insulated cords were already starting to replace the other types, except as you say for irons, kettles, etc.

Some of my greatest concerns over the ring is that it is not foolproof. Even when installed according to regulations, it is still possible (even if not likely) for somebody to connect several large loads at one end and overload a portion of the cable. Some of biggest problems are DIY modifications where people end up with an incomplete ring, or of course where a faulty connection causes one conductor to carry the full load.

Tex, I have no idea when the new colors were adopted in Austria, but here in Britain they started replacing our old red/black/green around 1970.

I prefer the old toggles to the modern rockers as well!