More dodgy tat

[kai]

Much Class 2 lighting these days (Not UK made) is just the manufacturer deciding not to bother with an earth connection.

 

[JohnW2]

Much Class 2 lighting these days (Not UK made) is just the manufacturer deciding not to bother with an earth connection.

That may well be true at the bad and/or illegal end of the market - but if you're talking about things which actually need to be earthed, then they clearly aren't actually Class II - regardless of whatever words and symbols the manufacturer may use.

Kind Regards, John

 

[EFLImpudence]

Does not the definition/ specification simply mean that it is not necessary (but would no harm) to earth its exposed conductive parts in order to achieve the required degree of protection against the risk of electric shock?

Have I answered that already?

I'm not sure. As I've said, apart from the general desirability of reducing the amount of exposed earth metal in a house, an item being Class II means that it dos not need earthing, but that earthing would 'do no harm' - so "must not earth" seems totally inappropriate.

I didn't say it would do no harm; I said it would be no more dangerous than class 1 items but it would be less safe than unearthed isolated metal parts.

That is the same as earthed baths or pipes when this earthing is not required. They are no more dangerous than bonded extraneous baths and pipes but they are less safe than if they were not earthed

As I have said before, there are class 2 ELV light fittings where the metalwork is one of the 12V conductors. These items should/must not be earthed.

 

[JohnW2]

I didn't say it would do no harm; I said it would be no more dangerous than class 1 items but it would be less safe than unearthed isolated metal parts. ... That is the same as earthed baths or pipes when this earthing is not required. They are no more dangerous than bonded extraneous baths and pipes but they are less safe than if they were not earthed

As I surely don't need to tell you, I agree with all that. The question is whether it is ('normally') ever appropriate for the manufacturer of a (true) Class II item to instruct that it "must not be earthed" - as you say, if their exposed metal parts are earthed they don't become any more dangerous than pipework etc.

As I have said before, there are class 2 ELV light fittings where the metalwork is one of the 12V conductors. These items should/must not be earthed.

That might possibly be an 'exception that proves the rule' (i.e. not a 'normally' situation, per above comment). However, having said that, what's necessarily wrong with PELV?

Kind Regards, John

 

[ericmark]

For another example earthing the braid on a TV coax may seem a good idea until one considered this may encourage a lighting strike on the aerial and cause untold damage as a result.

Aerials should be earthed. It does not encourage lightning strikes, it reduces the likelihood by discharging the ionised air. That is how lightning conductors work.

Lighting conductors are at least 25mm² often far larger there is no way a coax braid will take the currents involved so no way should it ever be earthed. One can use braid breakers to stop the DC connection and then earth after the braid break but NEVER earth an aerial with less than 25mm².

As to Class II and earthing in most cases there is no problem. If one is not sure then the 25 kV test from a PAT tester should satisfy if insulation is good enough.

But the fact that some one actually thinks you should earth an aerial shows how easy it is to make mistakes. "winston1" clearly does not see the danger in routing 5 billion joules through the house. We always fit lighting conductors to the outside of a building no one in their right mind would consider running it inside unless talking about a steel girder construction.

My concern is not the light in question I am sure to earth that is no problem. But people reading the answers may consider earthing other items which should not be earthed.

 

[EFLImpudence]

As I surely don't need to tell you, I agree with all that. The question is whether it is ('normally') ever appropriate for the manufacturer of a (true) Class II item to instruct that it "must not be earthed" - as you say, if their exposed metal parts are earthed they don't become any more dangerous than pipework etc.

Ok. So it is just down to semantics.

If you think an isolated bath should not be earthed, would it not be acceptable to say that it must not be earthed.

 

[ericmark]

As I surely don't need to tell you, I agree with all that. The question is whether it is ('normally') ever appropriate for the manufacturer of a (true) Class II item to instruct that it "must not be earthed" - as you say, if their exposed metal parts are earthed they don't become any more dangerous than pipework etc.

Ok. So it is just down to semantics.

If you think an isolated bath should not be earthed, would it not be acceptable to say that it must not be earthed.

What I am saying manufacturers are in a position to do a risk assessment having loads of data to help them. An electrician has limited data and so in the main countermanding the manufacturers instructions has to be deemed wrong.

There may be a special circumstance where the manufacturer is wrong but we had better be very sure before sticking out our neck.

In the main we use 4 or 6 mm cables to bond. But a shower is often feed with a 10 mm cable. I have seen where the 4mm cable is connected to the earth connection of a convenient socket so we could in fact have a 1.5mm earth cable.

Doing my own risk assessment I think there is far less risk following manufacturers instructions.

 

[RF Lighting]

What's bonding got to do with any of this? The discussion is about earthing.

 

[JohnW2]

As I surely don't need to tell you, I agree with all that. The question is whether it is ('normally') ever appropriate for the manufacturer of a (true) Class II item to instruct that it "must not be earthed" - as you say, if their exposed metal parts are earthed they don't become any more dangerous than pipework etc.

Ok. So it is just down to semantics. If you think an isolated bath should not be earthed, would it not be acceptable to say that it must not be earthed.

I don't think so - and nor would I necessarily call that 'just semantics'. To say that "I think that an isolated bath should not be earthed" is perhaps over-stating the case and, in any event, would only be a personal view/opinion of mine. Even though I do have my own view (the one you suggest), I recognise that there are 'pros and cons' and that there are some people (even some in this forum) who believe that, on balance, it is better that the bath be earthed. Under those circumstances, I would/should not be the one, and I doubt that anyone should be the one, to tell the whole world that they must not earth it. ... and, of course, a similar argument would probably apply tp (true) Class II items which have exposed-c-ps.

Kind Regards, John

 

[EFLImpudence]

I don't think that we are going to agree, so -

under what circumstances or for what reason would you earth an exposed-c-p of a genuine, properly installed class 2 appliance?

Have you earthed all of your class 2 tools (or any spoons ) ?

 

[SimonH2]

Lighting conductors are at least 25mm² often far larger there is no way a coax braid will take the currents involved so no way should it ever be earthed. One can use braid breakers to stop the DC connection and then earth after the braid break but NEVER earth an aerial with less than 25mm².

Earthing an antenna will make naff all difference to whether it gets struck - it's going to be "almost earthed" simply because it's connected to various bits of equipment which are at least lightly coupled to the mains - at most standing at around 120V AC if none of the equipment is earthed. In the grand scale of a lightning strike, that's nothing.

If the antenna is struck, then it matters not - the bolt WILL go down the cable. Before the strike has finished discharging, the cable will be just a plasma arc, but it WILL go down it. It'll also jump across to any other metalwork (eg cabling) within a few yards. Pretty well all electrical equipment in the house will be toast, as will much of the power wiring.
I recall reading an article in what was then Electronics World where someone has been called in to his local church somewhere in the alps. He described how the (recently inspected) lightning conductor had failed (fused) and the charge had diverted into the wiring. Anywhere there was a corner in the wiring, the magnetic effects had blown it apart. All the electronics was blown - but he did say that some of the older kit with shunt regulated power supplies did survive (albeit needing new shunt regulator devices).

Your braid breaker will have no effect whatsoever on this.

What earthing it will do is allow dangerous static charges to be discharged to earth other than through your receiver frontend. With thunderstorms in the vicinity, it's easy for an isolated aerial to collect hundreds, or even thousands of volts (depending on it's height and moisture content of the air) - earthing it will discharge that static. Also, the top of the pole and the antenna elements will act in teh same way as the primary function of the lightning conductors - by discharging some of the static charge in the air.
If you look at a lightning conductor installation you'll see that around the top of the building there are pointy spikes. This is deliberate as the sharp point creates corona discharge at much lower field strengths than any other shape. So when a thunderstorm is brewing, the field strength is concentrated around the points, generates a corona, and this will discharge the static in the vicinity. In many cases this will prevent the strike from happening. Actually catching and diverting a strike is a secondary function which may or may not succeed in keeping the energy out of the building.

But the fact that some one actually thinks you should earth an aerial shows how easy it is to make mistakes. "winston1" clearly does not see the danger in routing 5 billion joules through the house.

The mistake is yours. If the aerial is struck then that's going through the house regardless. As above, earthing the aerial may actually avoid the strike occurring in the first place, and it may well avoid expensive damage (and personal injury) due to nearby storms.
Also note that codes of practice are very clear that shared antenna systems must be earthed - one has to assume that those who came up with these took into account the various risks - and decided that the risk of electric shock from connecting equipment together from different supply zones was significant, while the risk from "attracting" a lightning strike down the cable isn't (or is less).

To finish off, tried a quick google search : https://www.google.co.uk/search?cli...t+is+the+field+strength+under+a+thunder+storm
Second hit (for me) is a document (PDF) from NIST which suggests the fair weather field is of the order of 100V/m, but during a thunderstorm can reach in the order of 4kV/m. Hmm.

 

[winston1]

For another example earthing the braid on a TV coax may seem a good idea until one considered this may encourage a lighting strike on the aerial and cause untold damage as a result.

Aerials should be earthed. It does not encourage lightning strikes, it reduces the likelihood by discharging the ionised air. That is how lightning conductors work.

Lighting conductors are at least 25mm² often far larger there is no way a coax braid will take the currents involved so no way should it ever be earthed.

I never suggested using the copper braid to earth an aerial. Aerials should be earthed using a copper conductor outside the house.
In some countries, I believe the USA and Germany, it is mandatory.

 

[JohnW2]

I don't think that we are going to agree, ...

I don't think we are actually disagreeing (see below).

... so - under what circumstances or for what reason would you earth an exposed-c-p of a genuine, properly installed class 2 appliance?

I answered that in my response to you well over a page ago:

In practice, I can think of only two situations in which one would normally contemplate earthing exposed metal parts of a "Class II" item ... Firstly, as in bernard's hypothetical example, if the earthing was going to happen 'by accident', and one didn't see the point in expending effort to avoid it getting earthed. Secondly(per recent threads) if one didn't relieve [should have been 'really'] believe/trust the fact that the item was satisfactorily 'Class II' (although one really ought to simply 'reject' such a product and get a proper Class II replacement).

Have you earthed all of your class 2 tools (or any spoons ) ?

See above. However, even though they are my personal views, I certainly am not going to jump up and criticise anyone who, for whatever reason (even if I consider it 'irrational'), feels the desire to earth exposed-c-ps of (genuinely) Class II items. As I said, AFAICS the only arguable 'downside' is that it will fractionally increase the amount of earthed metal around the house for one to touch. However, that would be virtually insignificant in a house full of pipework, radiators etc. which are connected to earth - so I couldn't say that the fractional addition to the amount of earthed metal resulted in any significant increase in risk (particularly if one was unnecessarily earthing something on the ceiling ).

Kind Regards, John

 

[EFLImpudence]

Ah, sorry, I couldn't have absorbed your previous answer.

I totally agree.

 

[JohnW2]

Ah, sorry, I couldn't have absorbed your previous answer. ... I totally agree.

There you go -I told you we weren't disagreeing.

However, you seem to be happier with the "must not be earthed" instruction than I am, even though we know that there others who would feel that earthing was acceptable, or maybe even desirable.

Kind Regards, John