Switching both live and neutral required for CE marking? - Page 1
Forum section: electronics / projects

author: voltlog
author_rank: Regular Contributor
timestamp: April 06, 2016, 06:36:19 pm
content: Hi,Recently in one of my videos(voltlog #40 - part 1) I did a teardown of two different wireless ac switching/control modules or IoT devices, you don't even know how to call them these daysI immediately noticed that both of these devices (Sonoff and BroadLink SP Mini) are only switching the live through the relay and have the neutral connected straight to the output.These are devices intended to offer wireless control of mains AC supply to various other devices. Considering there are various symmetrical plugs in use all over the world, one could easily insert the plug the other way around and have the live connected straight through the output, which is a serious risk of electrical shock.The Broadlink SP mini has the CE mark on its label. It was my knowledge (without being able to point to the source of this info) that in order to get CE marking you need to switch both live and neutral through the relay. I can't seem to find any detailed info on this, probably because the standards are not public and I will not pay insane amounts of money just to read them.Can anyone confirm this info? Or maybe give us some details on the particular directive that applies and what is required? If it's in the Low Voltage Directive (LVD) 2006/95/EC than this means, nearly all devices should comply to this rule if it were to exist. I would appreciate more info on this subject.Thanks!

author: Jeroen3
author_rank: Super Contributor
timestamp: April 06, 2016, 06:55:54 pm
content: I've yet to find something that actually does switch both. So I guess it's either ignored or not mandatory but advisory.Keep in mind that CE is self-certification, "CE until proven non conform". That is why it's crap.

author: Kjelt
author_rank: Super Contributor
timestamp: April 06, 2016, 07:01:02 pm
content: The problem is that in many european mains systems you do not know which conductor is the live and which one is the neutral since the plugs are symmetrical.So it does make sense to switch both.However AFAIK in Europe a device must be double isolated OR grounded so in both cases there is no risk.

author: rsjsouza
author_rank: Super Contributor
timestamp: April 06, 2016, 07:29:37 pm
content: Quote from: voltlog on April 06, 2016, 06:36:19 pmThe description indicates the product falls in the LVD (more than 50VAC/75VDCand less than 1000VAC/1500VDC) and the EMC (intentional radiator). However, I haven't heard of such stringent details regarding the power switch, but to be sure you would have to find among theLVD harmonized standardsthe one that is closer to the product - I am thinking something related to power strips (I think they also use single pole switches).(edit): clarified the voltage ranges for LVD

author: dmills
author_rank: Super Contributor
timestamp: April 06, 2016, 07:52:01 pm
content: I don't believe there is anything in the LVD as such (Note that 'low' voltage is less then 1kV AC, <50V is extra low voltage), but there may be things in some of the national standards implementing the LVD.Single pole switching is very, very standard in appliances, as well as in things like remote control power distribution units in server rooms and the like, there is no problem with it.Note that functional switching is NOT isolation, to isolate from a source of supply you do obviously need double pole switches having sufficient contact gap, but that is a different application to a functional switching use.At least in the UK, both phase and neutral are considered to be 'live' conductors as far as insulation and protection from direct contact are concerned (and we have polarised connectors), further I believe this is also the case in the US where the term is 'grounded conductor' for the neutral (as opposed to "grounding conductor" which is the safety earth).Regards, Dan.

author: dom0
author_rank: Super Contributor
timestamp: April 06, 2016, 10:37:43 pm
content: Not required. More expensive outlet strips are often marketed with it.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 06, 2016, 11:53:54 pm
content: I've read through IEC 60384-1; for certain classes of devices, you need to use double-pole switches, and fuse both lines (hot and neutral).This is mostly applicable to IT equipment (where the office/server mains may be e.g. 240V three-phase, thus there may be no neutral in a single-phase device), or medical devices (where H/N may be in much the same condition, and additional safety is needed).If your product does not need to comply with this standard, it's probably fine to switch and fuse the hot wire. (Ex: consumer goods, etc.)Tim

author: voltlog
author_rank: Regular Contributor
timestamp: April 07, 2016, 05:20:12 am
content: So far the general belief from your replies is that if the device is not within 'certain classes of devices' you are not required to switch/fuse both live and neutral.I don't think these intelligent sockets fall into any of those special categories, they are just consumer goods (well except for the SONOFF device which requires more advanced technical knowledge to correctly wire it) so the conclusion is they could use the CE mark, if they meet the other requirements as well.If I were to design one of these devices I would sure like to use a double pole switching relay just to get the extra safety.

author: Kilrah
author_rank: Unknown
timestamp: April 07, 2016, 05:30:21 am
content: Quote from: voltlog on April 06, 2016, 06:36:19 pmBut does the switching device itself have a symmetrical plug or not? As long as it doesn't it's OK as it's sure to always switch live. If it did, then yes that would be a problem.

author: voltlog
author_rank: Regular Contributor
timestamp: April 07, 2016, 05:35:42 am
content: Quote from: Kilrah on April 07, 2016, 05:30:21 amIn this case the Broadlink device itself doesn't have a symmetrical plug(I think it's an Australian plug), but if you use a plug adapter for European Schuko or US two blade you can plug it in both ways so the problem re-appears. The Sonoff device does not come with a plug, it is using screw terminals.

author: Kilrah
author_rank: Unknown
timestamp: April 07, 2016, 05:47:45 am
content: Well unless the adapter is shitty it should also enforce proper orientation. That pretty much goes beyond any cert though, a product as sold must usually comply to the local market, then whatever you do is on you. When you start using adapters there are for sure many very bad possible combinations but not much can be done about that.For the screw terminals - it's the installer's responsibility to do his job correctly.

author: Kilrah
author_rank: Unknown
timestamp: April 07, 2016, 05:52:12 am
content: Quote from: Kilrah on April 07, 2016, 05:47:45 amHeh how appropriate, I actually just saw that next to me after posting

author: Kjelt
author_rank: Super Contributor
timestamp: April 07, 2016, 08:23:36 am
content: Quote from: Kilrah on April 07, 2016, 05:52:12 am

author: voltlog
author_rank: Regular Contributor
timestamp: April 07, 2016, 08:35:38 pm
content: Quote from: Kilrah on April 07, 2016, 05:52:12 amNice plug adapter inception you have there...

author: IanB
author_rank: Super Contributor
timestamp: April 07, 2016, 08:45:05 pm
content: Quote from: voltlog on April 06, 2016, 06:36:19 pmThe amazing thing is that when the switch is activated the live is connected right through to the output also. How dangerous is that?

author: voltlog
author_rank: Regular Contributor
timestamp: April 08, 2016, 05:03:18 am
content: Quote from: IanB on April 07, 2016, 08:45:05 pmCertainly not the same thing. When the switch is off, one could expect to safely handle/touch the device that follows the switch.

author: ruffy91
author_rank: Regular Contributor
timestamp: April 08, 2016, 05:09:13 am
content: Quote from: voltlog on April 08, 2016, 05:03:18 amWhy should it not be safe? You can not touch any exposed contact wether it's neutral or live, can you?

author: voltlog
author_rank: Regular Contributor
timestamp: April 08, 2016, 05:41:06 am
content: Quote from: ruffy91 on April 08, 2016, 05:09:13 amThat's the thing, you said yourself, exposed contacts ora fault could happenin the device powered from these switches thatcould connect live or neutral to a metal chassis. Then, the user could think, hey the device is off so it must be safe to touch this metal chassis and it would get a serious electrical shock. That's the whole scenarios I'm thinking when I say it should be better to switch both live and neutral through these devices.

author: Kilrah
author_rank: Unknown
timestamp: April 08, 2016, 05:53:33 am
content: Quote from: voltlog on April 08, 2016, 05:41:06 amBut any device with a metal chassis would have to be earthed, and thus could not be plugged into your unearthed switching device.Anything you could plug in there would have to be a 2-prong device, which is designed to safely be reversible by using double isolation.

author: voltlog
author_rank: Regular Contributor
timestamp: April 08, 2016, 06:17:55 am
content: Quote from: Kilrah on April 08, 2016, 05:53:33 amThen consider this, two prong device being used through the smart socket which is turned off but has live connected straight to the output. User wrongfully thinks he can safely touch the terminals on the other end because the device is off and gets an electrical shock.Or consider this, user wrongfully connects the output of the Sonoff device to a lamp socket(E27 for example) and the live gets wired to the outer jacket because the user doesn't know live should always go to the center, end pin. He goes in there to change a light bulb and gets an electrical shock.These days, safety features should or could(if implemented) protect those who make errors themselves as well.

author: Kilrah
author_rank: Unknown
timestamp: April 08, 2016, 06:37:37 am
content: Quote from: voltlog on April 08, 2016, 06:17:55 amThis can't be since as pointed out earlier the smart socket is non-reversible, which ensures the live is what gets cut.Quote from: voltlog on April 08, 2016, 06:17:55 amAs said earlier a 2-prong device is made to be safe whatever the polarity, so again that can't happen.Quote from: voltlog on April 08, 2016, 06:17:55 amThis is a permanent fixture and requires professional installation. If you think you know what you are doing and DIY anyway, make that mistake, and also don't think not to touch the metal part of the bulb while changing it could be wise, you pretty much deserve your Darwin award. But chances are you'd have already killed yourself by trying to connect live wires to the screw terminals anyway.

author: Siwastaja
author_rank: Super Contributor
timestamp: April 08, 2016, 06:39:38 am
content: Quote from: voltlog on April 08, 2016, 06:17:55 amThis is the most probable scenario I can think of. E27 socket is not the safest to begin with, and it's extra dangerous when used with a non-polarized plug. Yet, in countries where non-polarized plugs are used (like here), practically 100% of the lamps fall in that category, everybody have them.Some E27 LED bulbs have had metal heatsink part connected to the thread terminal, causing the lethal voltages extend to even more user-touchable areas (large part of the bulb instead of just the thread). Authorities of course try to remove these from the market but they still do exist in the real world and must be taken into account.Also, even without those dangerous bulbs, the threaded jacket in E27 is dangerously easily accessible to the user.When the user knows that the light is supposed to be ON, at least they will be more careful when changing the energized bulb. When they expect the light to be off, it's a different story.This is not about a single point of safety; E27 and non-polarized plugs are to blame, kind of. Especially their combination. But safety is not about shifting the blame.This doesn't exactly answer whether it's required for CE marking, butdefinitelydo switch both poles in a device which could be connected to a non-polarized plug and which does have mains voltage outputs. IMO, it absolutelyshouldbe required if it isn't. It's an easy and meaningful safety improvement against accidental deaths. Of course, when the voltage is only used internally in the device and the switched mains is not directly user-accessible, then it doesn't matter.With polarized plugs, this is different, but it's easier to just design the device to work safely with both types of plugs.

author: wraper
author_rank: Unknown
timestamp: April 08, 2016, 08:24:38 am
content: Quote from: voltlog on April 08, 2016, 05:41:06 amThe device must be safe to touch regardless if it is on or off. If the device gets disassembled, it must be disconnected from the mains anyway. Also, there a hell a lot of the devices without any true power switch, just a standby mode.

author: dmills
author_rank: Super Contributor
timestamp: April 08, 2016, 12:47:17 pm
content: Both phase and neutral conductors are considered live for the purposes of protection for contact, safety isolation is a separate thing from functional switching.Safety isolation is always all poles and has specific requirements for contact gap and the like, this is a distinct concept from functional switching, and is typically met in domestic kit by simply fitting a plug that can be pulled out of the socket to provide isolation.Switched off, but still connected to the mains should never be seen as 'safe', unplugged, with the plug where you can see it and the power supply caps discharged with a 'chicken stick' is probably safe.The E27 lamp socket is an abomination, give me a bayonet cap any day.Regards, Dan.