"Double insulated, do NOT earth." Why? - Page 1
Forum section: electronics / repair

author: max.wwwang
author_rank: Frequent Contributor
timestamp: September 28, 2023, 07:23:37 am
content: Earthing is a seemingly trivial but actually very complex topic. I used to think it was simple and I knew about this, but I knew virtually nothing, which was dangerous. Only recently, I got to know a little bit about this, including the topic of isolation transformer, through discussions in this forum and watching YouTube videos. But there are still some questions I don't have an answer to. Here is one.On the casing of double-insulated appliances, often we see this on the label: "Double insulated, do NOT earth". I understand the reason why there is no NEED for earthing due to double-insulation, which means earthing does not provide more protection than without. But I don't understand why we should NOT (not need not) earth a double-insulated device. What's the RISK of doing this, beyond no more protection?I have googled this topic but have not found a clear explanation.

author: brabus
author_rank: Frequent Contributor
timestamp: September 28, 2023, 08:41:05 am
content: Earthing a double-isolated appliance is a no-go, simply because the producer has not defined a proper earthing contact for it. One could find a screw terminal, a hole in the metal case or even an actual earthing pole used in a different, earthed variant of the same appliance: please do NOT use them as earthing contacts. This would violate the manufacturer's specification regarding AC grid connection, potentially voiding the warranty and posing a risk for the end user.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: September 28, 2023, 09:00:33 am
content: Quote from: brabus on September 28, 2023, 08:41:05 amThanks. But I'm interested in what exactly the risk to the end user is.

author: brabus
author_rank: Frequent Contributor
timestamp: September 28, 2023, 09:37:46 am
content: The risk is given by the fact that the manufacturer has not defined an earthing strategy for the product, so the consequences of forced earthing are unpredictable. In other words, the manufacturer deemed the risk of failure of the double insulation as far more unlikely than the risk of failure of the earthing system.The most pesky circumstance is the failure of the earthing system on the AC side. If the main building earthing fails and another device is discharging current through the earth, the metal casing (that is supposed to be floating in a double-insulation device) would become energized, posing a risk to the end user.A practical example: suppose you decide connect the secondary side ground of a phone charger to earth, although the charger is isolated. Everything goes well, you hold the cellphone in your hand and nothing happens. But if the building's main earth connection fails (it's not that unusual!), you WILL become the discharge path of any current flowing through the earth path. So, it is better to stay floating (i.e.: double-isolated) than becoming an active part of the earthing system.

author: SeanB
author_rank: Super Contributor
timestamp: September 28, 2023, 09:51:39 am
content: The risk is failure of the internal parts, as often the internal insulation is not designed, or intended, to act as primary insulation, and can break down destructively with applied voltage, as the double insulation designation means the entire external insulation is designed to withstand mains, so internal parts do not need this.For small power supplies however the output can be grounded by other methods, this just means your ground path may now have currents flowing, that were normally suppressed by the internal filtering of the power supply.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: October 03, 2023, 03:10:58 am
content: That's what I wanted to look into. Thanks.Quote from: brabus on September 28, 2023, 09:37:46 amThis makes good sense. It's all about likelihood and assumptions.Quote from: brabus on September 28, 2023, 09:37:46 amThe person will indeed become the "discharge path of any current flowing through the earth path" but only if there is another earth fault in another device connected to the same AC source (such as the live wire inside touches its earthed metal chassis). In this scenario, it would requiretwofaults to really make earthing this double-insulated device a hazard (because with the earthing fault of the house, which means the path from the earth wire to the ground rod is broken, but without the second fault, which otherwise would connect the mains live wire to the house earth wire, it will only be that the personbecomesa part of the path for any current that may flow to the ground, but this isnotgoing to happen unless the second fault exists). Is this correct?

author: max.wwwang
author_rank: Frequent Contributor
timestamp: October 03, 2023, 03:16:58 am
content: Quote from: SeanB on September 28, 2023, 09:51:39 amThanks. But I'm not sure if I've understood this. We know there are double-insulated devices that have metal external cases. Are you referring to those with fully insulated (non-conductive) external cases?

author: SeanB
author_rank: Super Contributor
timestamp: October 03, 2023, 06:31:17 am
content: Double insulated with external metal means the insulation between inner mains times, and the metal part, is provided by 2 layers of insulation rated for mains use, or by having robust insulation, which is thicker. Grounding internal parts means the inner insulation may fail, or may flash over, as it is designed to float, while the casing is there to provide insulation, by using double layers, or robust insulation.

author: soldar
author_rank: Super Contributor
timestamp: October 03, 2023, 07:42:02 am
content: Quote from: max.wwwang on September 28, 2023, 07:23:37 amMaybe things are different in your part of the world but never in my many decades of tinkering and repairing have I come across such a label.In any case, a user is supposed to NOT modify a product in any way. An appliance passes a test of conformity for the market where it is sold and users are supposed to respect that because most users do not know what they are doing because they are not qualified to judge any changes. This goes without saying in any labels.Grounding is not a matter of just connecting some part to ground. All parts which need to be grounded need to be correctly connected and bound.If I saw such a label I would have to think why it might be there.It may be for sale in some part of the world where things are weird.It may be that the Asian manufacturer got a bad translation and really meant to say "Double insulated, does not need earth".It may be that some yahoo is under the erroneous but widespread impression, (including some on this board) that if a device has double insulation it is prohibited from using ground protection. This is not so.If done right earth plus double insulation is better protection than only one of the two. But the important thing here is that it has to be done right. You don't want some yahoo getting electrocuted because he (or she) thought he (or she) knew what they were doing.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: October 03, 2023, 07:51:01 am
content: Quote from: soldar on October 03, 2023, 07:42:02 amThis is not a bad answer! I've attached another example -- not a label but a part of the user manual. Essentially the same message.Quote from: soldar on October 03, 2023, 07:42:02 amYou are missing the point, or I have not made it clear. I have no intention whatsoever to add grounding to such a device. I only wanted to understand why is this.Quote from: soldar on October 03, 2023, 07:42:02 amMan that's exactly what I'm doing here!Quote from: soldar on October 03, 2023, 07:42:02 amGood point, that's a possibility -- seriously. But unfortunately, be assured this is not the case. The example below is from a European product, so it's not Asian (without suggesting Asian is bad in any way of course!).Quote from: soldar on October 03, 2023, 07:42:02 amAgain, be assured -- this is wrong. Follow this thread, for your safety's sake! (At least reply #3 above makes some sense, though I'm still challenging/testing that view.)

author: soldar
author_rank: Super Contributor
timestamp: October 03, 2023, 08:22:18 am
content: Quote from: max.wwwang on October 03, 2023, 07:51:01 amSpeaking of "missing the point" ... Read carefully what i wrote. I did not say or imply you were intending to add grounding to any device. I explained why a user manual might tell the user to not make any modifications... which is what you were asking: "why does it say this?"Quote from: max.wwwang on October 03, 2023, 07:51:01 amYou say it is wrong. I disagree. You cannot explain why it is wrong. You seem to interpret a vague statement to say what you want it to say and you extrapolate from there to imply what you are saying. If you assert that having double insulation plus grounding is dangerous then it is up to you to prove it.What is dangerous is not double insulation plus grounding. What is dangerous is having idiots tinkering with things they do not understand. Double insulation plus grounding is double protection if designed correctly by a competent engineer.

author: blauerscharik
author_rank: Regular Contributor
timestamp: October 03, 2023, 10:11:45 am
content: QuoteWhat if an idiot doesn't want to stay an idiot and tries to learn something? Everybody has to start somewhere.I never understood such comments.

author: soldar
author_rank: Super Contributor
timestamp: October 03, 2023, 10:21:14 am
content: Quote from: blauerscharik on October 03, 2023, 10:11:45 amI am not calling anyone an idiot and a person who wants to learn prudently is not an idiot. A person who jumps off a 100m cliff because he wants to "learn" if a 100m fall might hurt is an idiot.Consumer products are full of warnings to the consumer and they are there for a reason. A qualified technician or someone with adequate training and knowledge can, at his own risk, disregard the notice. A person who is not qualified does well to ask those who know, which is exactly what the OP is doing and well done.Those who think sticking scissors in power outlets is a way to learn anything are idiots learning about Darwin.

author: Zenith
author_rank: Frequent Contributor
timestamp: October 03, 2023, 10:35:16 am
content: Quote from: blauerscharik on October 03, 2023, 10:11:45 amYes and you will make mistakes, sometimes expensive ones, and get the odd shock in the course of it. It's sensible to take appropriate steps.I think the point here is it's unwise to modify a consumer appliance, subject to all sorts of regulations, in spite of a clear warning saying not to modify it in that way, with a chance of putting others at risk. You might have to explain your actions to a court.

author: blauerscharik
author_rank: Regular Contributor
timestamp: October 03, 2023, 10:42:15 am
content: QuoteTrue you didn't call anybody an idiot. But it seems that you are now paddling back a little by giving very dumb examples that have nothing to do with electronics.If someone wants to fix their broken mixer then I would say go ahead. Stupid would be having it plugged in and trying to unscrew the blades with your fingers or something like that. I know common sense is not that commonI just don't like reading things like "If your are not an engineer with 40 years of experience don't even think about repairing anything" (I'm exaggerating)But anyway this going off topic and let's not clutter this post unnecessarily.Have a good day.

author: soldar
author_rank: Super Contributor
timestamp: October 03, 2023, 11:03:47 am
content: My point is that consumer products carry warnings and disclaimers directed to the average consumer. That's all.If a CRT monitor says do not open it because it is dangerous that warning is directed to the average, non-technical user. It does not apply to qualified technicians.But the world is full of idiots who disregard safety notices and that is why every other day we see news of idiots who, disregarding warnings, got too close to a cliff and fell off or got too close to a wild animal and were attacked. And they record it on video for others to see. And others go and do similar things.Getting back to the original question, the warning is there to stop someone who thinks they know what they are doing but is not an idiot because idiots will disregard the warning and knowledgeable people will know what they are doing.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: October 03, 2023, 11:13:20 am
content: An example : a power drill.User drills into a live cable - if double-insulated, probably nothing bad happens.If earthed via an untested/unspecified route, unspecified currents can pass though parts that are not designed for it - possible arc flash & physical damage that could be a risk both at the time, and causing damage to safety-critical parts.

author: Gyro
author_rank: Super Contributor
timestamp: October 03, 2023, 11:50:51 am
content: Sometimes you don't get the option of deciding whether you appliance gets grounded or not. I've designed and taken to market a bunch of metal cased, double insulated, consumer A/V gear. This may or may not get eathed via the A/V connectors, antenna connectors etc. depending on what other equipment or environment the end customer has. It's not a problem safety wise (the double insulation happens in the internal SMPS board, spacings, insulation barriers, restraining where internal wiring might stray etc, but it does significantly complicate EMC testing because you are required to test in typical usage scenarios - interconnects attached, cable shields grounded and ungrounded.

author: soldar
author_rank: Super Contributor
timestamp: October 03, 2023, 01:05:12 pm
content: Quote from: mikeselectricstuff on October 03, 2023, 11:13:20 amThis could make sense at first glance but I disagree and I explain why.The whole point is to consider the external conductive housing is either (1) grounded via a conductor or (2) "grounded" via the user. If the housing becomes live, for any reason whatsoever, it doesn't matter if it's a drill or a refrigerator or a thingamagig, if it becomes live, what is better for the user: that (1) the current flow to earth via a cable or (2) that the current flow to earth via the user?Grounding external conductive parts that can be touched by personsalwaysenhances safety. It may be that double insulation is considered sufficient but (correctly) grounding the external parts will never decrease safety.The problem might come when someone read that "grounding always increases safety" and he goes and grounds the device in the wrong (internal) place which should not be grounded.Now someone will come up with a scenario where the ground conductor was mistakenly connected to 400V and it would have been better if the device wasn't grounded. Or something like that.

author: soldar
author_rank: Super Contributor
timestamp: October 03, 2023, 01:11:30 pm
content: Quote from: Gyro on October 03, 2023, 11:50:51 amYes, A/V introduces other considerations about ground loops, interference, etc. But I think here we are considering solely the safety of users.But you are right that often you do not get to decide that the device not be grounded.If I have a double insulated drill and I am drilling into a grounded pipe or metal post or whatever which is grounded then the drill itself is grounded and it would be absurd to say that if you have a double insulated drill then you cannot drill into grounded metal objects because this would cause the drill itself to become grounded.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: October 03, 2023, 01:34:48 pm
content: Quote from: soldar on October 03, 2023, 01:05:12 pmthere is also the situation where there are external conductive parts which are not in contact with the user. E.g. the chuck of the aforesaid motor on a drill with a plastic handle.QuoteIn the UK at least, that is a significant enough possibility that regs require EV chargepoints (and hot-tubs I think) to include protection against it. Neutral and Earth are typically bonded togther where the service enters the house.An upstream neutral fault can render the earth connection live relative to actual earth. This is not normally a big risk, as everything inside the house, e.g. water pipes, is bonded to the mains earth so there is no voltage differential, however an exposed outdoor conductor, like the body of a charging EV can be come live with respect to "real" earth.

author: brabus
author_rank: Frequent Contributor
timestamp: October 03, 2023, 01:51:48 pm
content: Quote from: soldar on October 03, 2023, 01:05:12 pmSorry, this is just plain wrong, at least in the EU.Grounding the metallic chassis of a double-insulation appliance voids the EN60335 (I will provide the exact passage in the norm for completeness' sake).

author: soldar
author_rank: Super Contributor
timestamp: October 03, 2023, 02:01:26 pm
content: Quote from: mikeselectricstuff on October 03, 2023, 01:34:48 pmNote that the rule is not concerned with whether a part is normally touched by the user during use. The rule states that any conductive parts which can or may be touched by a person must be protected by an acceptable means (grounding or double insulation).With a drill the user will touch the chuck while setting up the drill bit and at other times. The chuck is an exposed part and needs to be protected.Even parts which are inside a housing but are reachable by small fingers (via vent holes etc) are considered "touchable" and therefore need to be protected.We could also talk about sticking pointy knives into toasters in an attempt to fish out the bread that got stuck. Every time I do it I am admonished it is dangerous.

author: soldar
author_rank: Super Contributor
timestamp: October 03, 2023, 02:04:07 pm
content: Quote from: brabus on October 03, 2023, 01:51:48 pmPlease do. If it is what I am thinking I believe it does not say what you think is says and it has been misinterpreted. But let's have the text and see.ETA: i find it incredible that you have to pay to get the text. It is legislation, the people are assumed to know it, it should be free.

author: brabus
author_rank: Frequent Contributor
timestamp: October 03, 2023, 02:34:35 pm
content: Excerpt from the IEC61558:(still searching for additional normative references, it takes some time to find the exact topic in the norm).

author: soldar
author_rank: Super Contributor
timestamp: October 03, 2023, 02:36:49 pm
content: Quote from: brabus on October 03, 2023, 01:51:48 pmJust to clarify: I have had this discussion before and some years ago I had to delve quite deeply into the regulations etc. I found many people repeated this, which I consider a myth, but no one was able to cite the regulation which supposedly said that. Nobody. Nobody has been able to show any regulation prohibiting both protections and nobody has been able to make a clear case against using both. Only repeating unexplained hearsay. That carries no weight with me.The closest I found when reading the regulations was something which was probably misinterpreted by someone and by way of the telegraph game became so distorted that it made no sense and has become this myth.What I remember is something like this: If a device is certified as beingbothgrounded and double insulated the when in use it must be grounded and double insulation is no excuse to avoid the grounding.Anyway, I am willing to be proven wrong if (1) a clear case can be made on technical, engineering grounds or (2) a text of a law or regulation can be cited. I will accept either.

author: soldar
author_rank: Super Contributor
timestamp: October 03, 2023, 02:54:31 pm
content: Quote from: brabus on October 03, 2023, 02:34:35 pmAs you yourself said, regulation EN-60335 establishes the general requirements for electrical/electronic appliances for household and similar purposes.I had the text some years ago but I do not have it now.As with all laws and regulations it is complex language and defines things like "ordinary persons", "basic insulation" , "supplementary insulation" and many other terms very specific to the regulation.It is not like some people think that it will say "if you use double insulation you cannot use grounding".Anyway, let's see if someone can get the text of EN-60335.Both in America and in EU the laws incorporate codes which are private and copyrighted and IMHO this is terribly wrong. If it is the law it needs to be available to the public for free. /end of rant.

author: soldar
author_rank: Super Contributor
timestamp: October 03, 2023, 03:06:32 pm
content: Quote from: brabus on October 03, 2023, 01:51:48 pmI have found in my filesIEC 60335-1, Edition 4.1, 2004-07, -- Household and similar electrical appliances –I am not about to dig into it but I will be happy to send it to whoever wants it. Or, even better, maybe someone can find a newer version.

author: soldar
author_rank: Super Contributor
timestamp: October 03, 2023, 03:16:44 pm
content: https://www.pat-testing-course.com/blog/faqs/electrical-appliance-classes/Class I - The protection inside class 1 appliances combines together the protection of insulation and a means of connection to the earth connection protective conductor (Earth wire).Class II - These appliances are known as double insulated due to the presence of at least two layers of insulation. The earth connection present in Class I appliancesis not requiredfor safety.Note it does not say it is prohibited. It is not required.

author: soldar
author_rank: Super Contributor
timestamp: October 03, 2023, 03:36:44 pm
content: OK, I think I found the source of confusion:Quote

author: JohanH
author_rank: Frequent Contributor
timestamp: October 03, 2023, 03:48:02 pm
content: Try grounding consumer audio equipment and you might get trouble with 50/60 Hz hum in audio output.

author: soldar
author_rank: Super Contributor
timestamp: October 03, 2023, 04:03:09 pm
content: Quote from: JohanH on October 03, 2023, 03:48:02 pmTry grounding your teenager and you might find out you have even less authority than you thought. Yaketty Yak!

author: brabus
author_rank: Frequent Contributor
timestamp: October 03, 2023, 09:56:24 pm
content: From the IEC 60601:QuoteThe usage of Class II appliances is rather typical in the medical area; the connection of accessible conductors to the earth is explicitly forbidden, for the reasons we described in the previous posts (i.e.: failure of building's main earthing).The medical appliance is a classic example: would you trust a wire permanently connected to earth to be also connected to your body for a long period of time? After working on a TN-C-S system and seeing the result of the interruption of the local earth connection, I would most definitely rather not.I am actually searching for the excerpt from a more detailed norm I had to deal with, which obliges the OEMs to write in the user manual NOT to connect the earth to any accessible metal surface. We had to deal with this issue in the past and had to update the user manuals; I am going to contact the colleague which followed the topic with me in order to retrieve the norm.

author: soldar
author_rank: Super Contributor
timestamp: October 03, 2023, 10:27:58 pm
content: Quote from: brabus on October 03, 2023, 09:56:24 pmLook, you are fishing around trying to cloud the issue. We are talking about domestic appliances which are, as you said, regulated by EN 60335-1. We are not talking about the other thousand regulations about medical, or industrial or other specialized cases.And user manuals are not the law. They can be and often are written by people who are mistaken. And this issue seems to have mistaken many people. But if you want to know the law you quote the law, not a user manual written by some yahoo who is being paid less than minimum wage.EN-60355-1 explicitly approves of grounding plus double insulation by saying those devices are classified as class I.I cannot find anything in EN 60355 to the contrary. And it seems you can't either. I have already said I like to see it.You are not trying to find the truth, rather you are trying to defend your original position no matter what. It seems to me you are now just dishonestly trying to defend a position you know is wrong.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: October 04, 2023, 07:02:29 am
content: Quote from: soldar on October 03, 2023, 08:22:18 amI accept this is indeed true. I'm now only extrapolating from what seems to be able to rationalise the subject warning massage. It's a jump.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: October 04, 2023, 07:12:00 am
content: Quote from: soldar on October 03, 2023, 11:03:47 amAgreed. But this really does not explain why the message cannot simply be "need not" as I asked at the very beginning.Quote from: soldar on October 03, 2023, 11:03:47 amAgreed. Consumer products are designed to be fool-proof in a way somehow ridiculous to "idiots" like me who like to tinker with things.Quote from: soldar on October 03, 2023, 11:03:47 amUnable to agree. See above.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: October 04, 2023, 07:16:09 am
content: Quote from: Gyro on October 03, 2023, 11:50:51 amWhat's exactly what once puzzled me -- double-insulated appliances (AV gear) with only two wires in the mains lead. But I now know double-insulated appliances may have full metal cases. There might be performance, not safety, reasons why they should not be earthed. That's a possibility.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: October 04, 2023, 07:20:54 am
content: Quote from: soldar on October 03, 2023, 01:05:12 pmThanks for your clear, absolute, and categorical statement. That's what I thought, hence the question when seeing the subject warning message, which does not reconcile with this.Let's find out if this is indeed true, which means the message is incorrect, or at least inaccurate.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: October 04, 2023, 07:25:50 am
content: Quote from: soldar on October 03, 2023, 01:11:30 pmNo, the message itself does not say it's about safety, though the example I provided (from an instruction manual) sounds like it's concerned with safety (with "extreme care"). Let's explore all reasons why double-insulated appliances should not, or need not, earth, without limiting to safety.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: October 04, 2023, 07:35:49 am
content: Quote from: mikeselectricstuff on October 03, 2023, 01:34:48 pmGood to know. It'll be great if we can see the regulation about this.Quote from: mikeselectricstuff on October 03, 2023, 01:34:48 pmTrue.Quote from: mikeselectricstuff on October 03, 2023, 01:34:48 pmDespite (relatively) low likelihood, this seems to be the primary (if not only) scenario where earthing a double-insulated device might become a hazard. As I said above, however, this would require another earth fault in another device in the same AC supply line, if I'm not mistaken.By no means am I saying, that the requirement of two faults existing simultaneously will make this hazard not a risk. This definitely is a scenario that should be seriously considered and weighed up in designing the fault-safe strategy of a product (and the whole system, including the power grid).

author: max.wwwang
author_rank: Frequent Contributor
timestamp: October 04, 2023, 07:42:15 am
content: Quote from: soldar on October 03, 2023, 02:54:31 pmAgreed 100%.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: October 04, 2023, 07:45:14 am
content: Quote from: soldar on October 03, 2023, 03:06:32 pmGreate, message sent to you requesting a copy. Thank you.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: October 04, 2023, 07:56:35 am
content: Quote from: soldar on October 03, 2023, 10:27:58 pmIn one of your posts above I think you accepted either a clear case on technical or engineering grounds, or direct quote from mandatory regulations.Arguing on technical grounds does not need to constrain the subject to consumer appliances. It's not about who's right who's wrong. Let's try to find the truth.Quote from: soldar on October 03, 2023, 10:27:58 pmI admit this is a strong support for your argument. However, have you thought about the double-fault scenario mentioned above, which would make earthing the metal case of a double-insulated device a real hazard? What's your response to that? (Again, I'm not saying the likelihood of that scenario is high; I'm only saying that's a possibility, and that if it happens, the risk is real.)

author: Gyro
author_rank: Super Contributor
timestamp: October 04, 2023, 08:24:08 am
content: Quote from: max.wwwang on October 04, 2023, 07:16:09 amNot performance specifically (although it can help avoid audio ground loops as somebody mentioned). The main reason is that you are designing products for the international market and a lot of countries don't have earthed mains outlets.

author: soldar
author_rank: Super Contributor
timestamp: October 04, 2023, 08:27:07 am
content: Quote from: max.wwwang on October 04, 2023, 07:20:54 amI think you are still missing my main point which is that the message is directed at the common user who knows little or nothing about electricity and it is not directed to product designers, engineers, technicians and other qualified people.To me the message does not say or mean "this action should never be done" but rather it means "common users should not do this" and the reason is not that it should never be done but rather that common users are not qualified to do it and should not attempt to do it.If I see on the cover of a HV device, like a CRT monitor, a notice that says "Caution: do not remove this cover" I interpret that to mean the final user should not remove it and not that it should not be removed by anyone under any circumstances.I do not think I can express it any more clearly.And, again, a user manual can contain errors as it was probably written by some low-paid minion who can be mistaken on some points and this error seems to be quite common. The only way to find out is to ask the author.Some years ago I downloaded a technical paper from TI and I found some mistakes. I emailed the author about them and he shot back with an angry and rude email telling me that since I had paid nothing for the download I could not demand any level of quality.I emailed the head of that department and she very politely and graciously apologized and assured me TI would always try their best and the errors I pointed out would be corrected. The paper was very good, high quality stuff written by a very competent engineer, but everyone makes mistakes.Regarding the grounding of double insulated appliances, over the years I have had this discussion with many people who believed it was not allowed but no one ever has shown me a regulation forbidding it or a technical explanation of why it would be forbidden. It is just one of those things that has become true by mere repetition.People will believe anything even if it goes against their own common sense and against what their senses are telling them. It is extremely difficult to convince some people that what they have believed for so long is mistaken even though they formed the original opinion just because someone told them so and now they cannot be convinced they are mistaken even when showed a mountain of evidence. It is human nature.In summary, it is perfectly acceptable to use grounding and double insulation in consumer appliances and they will pass all CE (and I believe UL) tests.What they don't want is final users, who are not qualified, grounding a device badly, starting a catastrophe and then saying "As God is my witness I thought grounding always increased safety".I will send you the regulation.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: October 04, 2023, 08:29:28 am
content: Quote from: Gyro on October 04, 2023, 08:24:08 amOk. I get that. But to me it's a really weak (or hardly relevant) point on the subject question.

author: Gyro
author_rank: Super Contributor
timestamp: October 04, 2023, 08:38:04 am
content: I'm really not sure I care whether it's weak in the subject question. I simply pointed out that you don't get the choice of whether your consumer A/V product is going to be externally grounded or not. You asked the reason why they are double insulated in the first place, and I told you.

author: soldar
author_rank: Super Contributor
timestamp: October 04, 2023, 08:59:30 am
content: Quote from: Gyro on October 04, 2023, 08:38:04 amI do not see how it is "weak". To me it seems very relevant to the issue being discussed.

author: horo
author_rank: Regular Contributor
timestamp: October 04, 2023, 09:47:35 am
content: Quote from: max.wwwang on October 04, 2023, 07:56:35 amThe important difference is that Class II isinherently safe, whereas Class I depends on the correctness of the surrounding installation. So you can plug your Class II unit (known to be in good working order) into any socket in your lab or your customer's workshop and use it safely, whereas with Class I you have to rely on the correctness of the (external) PE.

author: themadhippy
author_rank: Super Contributor
timestamp: October 04, 2023, 12:36:08 pm
content: QuoteAnd in earth free locations?

author: soldar
author_rank: Super Contributor
timestamp: October 04, 2023, 12:53:33 pm
content: Quote from: max.wwwang on October 04, 2023, 07:56:35 amNow we are getting into fringe territory where wearing a seat belt in a car could kill you and smoking two packs a day could prolong your life. I am not interested in this.Fringe and absurd cases notwithstanding, grounding touchable conductive parts of appliances increases safety.And, contrary to widespread but erroneous belief, it is not forbidden by the regulations at all to have double insulation plus grounding. In no way do they interfere with each other and their protections add up. The user is more protected with both.

author: themadhippy
author_rank: Super Contributor
timestamp: October 04, 2023, 01:03:10 pm
content: QuoteNot got the latest version to hand to quote chapter and verse,but from a previous version of the uks wiring regs5.8.1 - Class II equipmentClass II equipment has reinforced or double insulation. As well as the basic insulation for live parts, there is a second layer of insulation, either to prevent contact with exposed conductive parts or to make sure that there can never be any contact between such parts and live parts. The outer case of the equipment need not be made of insulating material; if protected by double insulation, a metal case will not present any danger. It must never be connected with earth, so connecting leads are two-core, having no protective conductor. The symbol for a double-insulated appliance is shown in {Fig 5.20}.

author: soldar
author_rank: Super Contributor
timestamp: October 04, 2023, 01:25:41 pm
content: Quote from: themadhippy on October 04, 2023, 01:03:10 pmAgain, for the umpteenth time. If it has Earth then it is classified as class 1. It does not say a device cannot have both. It says if it has ground then it is class 1.Now show me where it says a class 1 device cannot have both.Man, this is getting repetitive. And boring.

author: themadhippy
author_rank: Super Contributor
timestamp: October 04, 2023, 02:55:17 pm
content: Quotemaybe not what it does say though isQuote

author: soldar
author_rank: Super Contributor
timestamp: October 04, 2023, 03:12:42 pm
content: Quote from: themadhippy on October 04, 2023, 02:55:17 pmMan, really. You need to read and understand and comprehend what has been said already several times.That is referring to class 2. I will repeat since it does not seem to register: Class 2. Ok. Class 2. Make a mental note of that. Class 2.Any device with a grounded cord is classified as class 1. If it has a ground it is class 1. Which is different from class 2. What you quoted applies to class 2. A class 2 appliance cannot have a ground cord because, by definition of class 2, it would be excluded.I don't know if some people are dense or trolling.Oh, fruck it! I'm outta here!You all have fun and drive carefully.

author: themadhippy
author_rank: Super Contributor
timestamp: October 04, 2023, 03:42:44 pm
content: exactly what is your question in simple terms? it seems to me you are asking if an earthed appliance can also be class 2,if thats the case then no,as the above quoted bit of regs show,if its class 2 no earth if its got an earth it aint class 2

author: coppice
author_rank: Super Contributor
timestamp: October 04, 2023, 03:55:22 pm
content: Quote from: soldar on October 04, 2023, 03:12:42 pmThe wording doesn't say that any outer metal must not be connected to earth through the power cord. Its makes a generic statement that it must not be earthed. That doesn't seem to make sense. Its harmless if earthed by being pressed against another metal cabinet which is earthed. It would be unsafe if it were not.

author: Gyro
author_rank: Super Contributor
timestamp: October 04, 2023, 04:10:54 pm
content: Quote from: coppice on October 04, 2023, 03:55:22 pmClass II products don't come with 3 core power cords - they just don't, ever. If they did then there would be the issue of what to do with the 'case' core when it reached a 2 pin plug. It's never going to happen.Yes, it's harmless, safety wise, if an earthed conductor (including human) is pressed against the case of a Class II appliance.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: October 04, 2023, 07:54:29 pm
content: Quote from: horo on October 04, 2023, 09:47:35 amThat's a good point. No disagreement here.Devices ofbothclasses are safeonlyunder certain assumptions (that's why I believe there is no absolute safety, and "safe" is always relative). There is no point in talking about safety in an ideal world. I guess the added strength of insulation by double insulation or reinforced insulation, above basic insulation (using the terms in the regulation), is deemed equivalent to the protection afforded by PE (taking into account the likelihood of its failure of course). And we are not talking about anyone doing dumb things (like breaking the case and poking their fingers onto the live wire); it's just normal/average use scenarios, taking into account abnormal, but not deliberate (that's sabotage), scenarios.However, back to the original question, consider the "double-fault" scenario (which I think is the same as the scenario I saw when googling before posting the question here -- it's either not that clear or I didn't fully get it), it seems to me -- at least -- in this scenario, earthing a class II device is detrimental to safety, contrary to the absolute and categorical statement that "earthingalwaysenhances safety". That's the crux of the question.I have not seen a compelling argument against this "double-fault" scenario yet.

author: max.wwwang
author_rank: Frequent Contributor
timestamp: October 04, 2023, 08:02:59 pm
content: Quote from: soldar on October 04, 2023, 12:53:33 pmHey, we are having a serious technical discussion here. There is a caseformy argument (in reply #3), which is objective, clear, and assessable without ambiguity. However, you are now using words like "fringe" and "absurd", which are both subjective. These do not fit together.As I said, safety is all about risk and risk is about likelihood (and consequence). As long as some hazardous scenario is possible and real, it deserves a serious assessment (though we may decide to ignore it, consciously, if the risk is low).If you don't have a compelling argument against this, it appears to me that your clear, absolute, and categorical statement that "earthingalwaysenhances safety" (my paraphrase) is wrong.I assume we all understand the meaning of "always", or "never".

author: max.wwwang
author_rank: Frequent Contributor
timestamp: October 04, 2023, 08:40:36 pm
content: Quote from: themadhippy on October 04, 2023, 01:03:10 pmThis is useful. Note that this is not "hearsay". The language cannot be clearer -- "Itmust neverbe connected with earth".

author: max.wwwang
author_rank: Frequent Contributor
timestamp: October 04, 2023, 08:50:12 pm
content: Quote from: soldar on October 04, 2023, 03:12:42 pmI understand what you are saying. Your argument that the subject warning message is wrong, or mistaken, is partly based on anassumptionthat many average users are idiots who have to be warned by exaggerated, but technically incorrect, messages. I have some sympathy for this view because I agree that consumer appliances do need to be designed to be fool-proof to some degree.However, we (actually you) will have to make anotherassumptionthat the lawmakers (or technical experts behind the safety regulations) are also idiots, that they don't understand earthing a double-insulated device will simply make them class I without needing such "erroneous", and misleading messages like "Itmust neverbe connected with earth".It takes much more for me to believe they are also idiots!

author: max.wwwang
author_rank: Frequent Contributor
timestamp: October 04, 2023, 09:36:41 pm
content: Quote from: themadhippy on October 04, 2023, 03:42:44 pmI think my question has been framed very clearly and specifically in the very first post.

author: themadhippy
author_rank: Super Contributor
timestamp: October 04, 2023, 09:54:46 pm
content: max sorry, my question was aimed at soldar .

author: max.wwwang
author_rank: Frequent Contributor
timestamp: October 04, 2023, 10:28:12 pm
content: Quote from: themadhippy on October 04, 2023, 09:54:46 pmAh I got you. Not a problem!

author: MarginallyStable
author_rank: Regular Contributor
timestamp: October 04, 2023, 11:39:40 pm
content: EN-60335 section 27 "Provision for earthing""Class 0 appliances, class II appliances and class III appliances shall have no provision for protective earthing. Class II and class III may incorporate earth for functional purposes"Class II being double insulated

author: brabus
author_rank: Frequent Contributor
timestamp: October 05, 2023, 08:21:05 pm
content: Quote from: soldar on October 03, 2023, 10:27:58 pmNo need to defend anything: the truth is the norms.Plus, accusing someone of dishonesty is a way of describing one's self.So, the EN60335 refers back to the 61140, which states:"This requirement shall be fulfilled when the equipment is properly installed". Fixing an earth wire to an insulated device does NOT make it Class I. It makes it a dangerous bodge.But let's go deeper and search among other norms, such as the CEI 64-8/4, paragraph 413.2.2.4, or the EN60335/2/23. Here the connection of conductive parts that could become in contact with hair or skin isexplicitly forbidden. No discussion about Class I or II, just don't connect the PE to them. Ever.What are you going to do if you see this symbol (please note, it hasnothingto do with Class I or II)?https://www.iso.org/obp/ui#iec:grs:60417:6032

author: tooki
author_rank: Super Contributor
timestamp: October 06, 2023, 01:01:31 pm
content: Quote from: soldar on October 03, 2023, 03:36:44 pmGenuine question, then (not being argumentative, I am actually curious): How does Apple have its laptop chargers certified as double-insulated? These chargers use a detachable, modified C8 mains input with a ground stud, onto which either an earthed cable (using a C7 plug and the ground stud) or an ungrounded mains plug (“duck head”) can be snapped. (In the past, there also existed ungrounded cable versions.) This means that the same charger can be floating or grounded, and consequently, the laptop’s aluminum enclosure can be floating or grounded. (When floating, many users can feel the tingle from the interference suppression capacitors.) The ground stud is the only external metal item on the charger body itself (since it’s always covered by the duck head or cable when in use), but the DC plug has exposed metal, including the ground.I, too, would interpret the section of the standard to prohibit a ground on a class II appliance, in that by having one it ceases to be class II.Yet clearly the Apple chargers are compliant (since they are externally certified, not to mention under enormous scrutiny by the media, etc), with the double insulation symbol on them, yet have an optional ground. There must be some detail we are missing, methinks.