Class II appliance requirements

[Chad]

I was under the impression that Class II appliances had to have physical insulation e.g. plastic or other non-conductive material between the live parts and accessible metal parts, hence the term "double insulated".

I've got a Class II electric convector heater with a metal case. The heater element is metal and the incoming mains connects to it via a spade terminal. If the spade connector becomes loose there is plenty of length to the live wire to allow it to touch the metal case.

The case is painted, but surely this is not enough to class it as double- insulated? In effect there is only an air gap between the live connector and the case.

The heater is a DeLonghi, it has the double-insulated symbol on the rating sticker and the fitted cable has no earth wire.

Any comments?

[Brian Gaff]

Sounds like crap. How much would it cost to attach insulation after all, not a lot. Maybe the tested one did have this, but the heat made it come unstuck so they left it out. Might be worth a chat to trading standards.

Brian

[Chad]

I would hope that an earth connection would not be glued on! A 3-core cable and a screw/shakeproof washer would do the trick.

It's several years old - possibly about 7 or 8 - so TS won't be interested.

[meow2222]

The usual way to deal with this is to cable tie the L&N wires together so that if one comes adrift it can't reach the case.

NT

[Martin Brown]

Sounds a bit naughty to me, but then I have little confidence in these cheap and nasty fan heaters anyway. Same problem too with 1L kettles designed down to a price and intended to last guarantee period + 1 day.

My parents had one of those "safe" oscillating tall fan heaters (brand redacted) and it gradually ate through the insulation on its own power cable with the incessant twisting and turning until the base caught fire. The scorch marks and molten plastic it left on the carpet were most alarming.

Being a two core feed it didn't generate earth leakage so it managed to get the flame retardant plastic well alight before the 13A fuse blew.

I prefer all my metal cased appliances to have an earth. YMMV

[Chris J Dixon]

I once hired a carpet cleaner which was double insulated, but had a metal outer case, presumably for durability. Unfortunately, the cable had slipped through the grip, whilst still functioning, and the live conductor had made contact with the casing. I only realised there was a problem when it sparked to a radiator.

Luckily no harm done, and hire fee waived, but it could so easily have been much more serious.

Chris

[therustyone]

Go into any store and you will find dozens of metal floor and desk lamps with only two-core mains connections, ie no earth at all to protect against wiring defects. How safe are these? I can measure 40 odd volts on the metal with a DVM on the chrome plated ones I own. Not a fault, just capacitive leakage from the internal wiring.

rusty

[Chad]

Could have been nasty!

I don't mind *if* they are properly insulated. This one, to me, doesn't look it. And it's illegal to add an earth to it, despite the fact it would make it safer.

[Chad]

The live and neutral go their separate ways soon after entry. The live bends round to the spade terminal near the case, if it comes loose (unlikely, but we're talking possibilities here) then I suspect just the wire straightening from its bent-round shape will be enough to make it touch the case. There's nowhere to cable tie it to where it would keep it out of the way.

[Tim Watts]

Class II can be satisfied in two ways that I know of:

1) There is supplementary insulation in addition to the basic insulation between the live parts and the user;

2) The live parts are contained in one or more layers of reinforced insulation (so this is not "double" insulated per se.

Basic insulation means the insulation on the actual wires for example.

Supplementary insulation could be a plastic enclosure, cable sheath or lots of other things.

In either case, an air gap may suffice.

In your example:

I would say if the wires were crimped, it might be OK to claim the air gap as supplementary insulation.

But I'm in agreement with your theory that the spades might fall off, especially with something that gets hot.

If I'd built this, I'd have earthed the case and called it Class I. Really cannot see any reason the manufacturers did not especially DeLonghi who do not have a habit of making crap IME.

[Tim Watts]

Is it? And how would that be any different to you building a mains powered widget (hobby electronics) with an earthed metal case as was common in the 70s?

And who cares - earth if if you feel happier.

I rescued a metal desk lamp where the "touch" electronics had packed up.

They used a 3 core feed to the main lamp with the "earth" wire as sensory feedback.

I simply stuck a plug in this part (the sensor module was nearer the plug than the lamp) and earthed the green wire.

I did happen to have a Megger lying around so I did do a quick 500V IR check and an impedance check on the earth to casing connection. Both were fine.

[Chad]

Well, the advice is that you "must NOT" earth a Class II appliance. AIUI if there's a fault on another appliance or the circuit, the earth can briefly become live until whatever protection there is kicks in.

That's what I don't grasp. Unless, as above, because Class II is supposedly inherently safer than Class I because the wiring should never come into contact with the case.

I'd rather understand the whole thing first; plus, as I said, the advice is to never earth a Class II.

I have a Megger PAT tester (pedants: yes, I know) and my heater tests fine

- as it would, with everything as it was built.

[Chad]

Yeah. Most odd. It wasn't even made in China but Italy. (According to the same label that gives it Class II rating, natch!)

[Tim Watts]

Whoever wrote that was talking rubbish.

The same applies any Class I device. And potentially any earthed metalwork in your house like all the pipes if you get a big enough fault.

So ignore that.

Class II is inherently safer IMHO if it's in a plastic enclosure. If it's in a metal enclosure, then unless there is a very robust barrier between the live parts and the case, I'd rather see it earthed for everyday use.

Clearly there are Class II appliances where it is debatable that there is a "robust barrier".

I think a lot of it is so they can sell the widget all over the world with a 2 pin plug on.

Go back to early british products and if it had a metal case, it was usually earthed.

Are you happy leaning against your radiators on a concrete floor with bare feet? If so, earth the appliance - you will not be in any more danger.

[Brian Gaff]

In that case areyou sure its not been got at before and a piece left out? Brian

[meow2222]

Many times I've seen these ties omitted though, then there's nothing to stop a live to case contact. I put it down to chinese factories cutting corners.

NT

[ARW]

Just one. What's protecting the metal case from the heating element?

[Chad]

There's no earth wire in the (fixed) cable and it's stickered as Class II.

[Chad]