Huge SAFETY CONCERN, DPST switch used HALF mains and HALF DC....  - Page 1
Forum section: electronics / projects

author: peteb2
author_rank: Regular Contributor
timestamp: October 04, 2017, 10:37:57 pm
content: This is a question on electrical safety and possibility of someone being electrocuted.I have to ask is it safe practice to use an RL3-4R series rocker switch such that one set of contacts can switch mains power 230Vac while the other set can switch 12Vdc?Here's a link to a pdf of the switch:http://www.phaseda.com/catalog/Spec_RL3-4R.pdfThe appliance is an LED lamp used in the field etc by a TV News crews. The issue of concern is that the 12Vdc connector on the appliance is a male pin XLR-4 and the pins can be easily be made contact with by the users' fingertips if the 12V is not in use.If the light is running off mains however (via its fix-wired flex) the only isolation is the few microns of air in the space inside the RL3-4R rocker switch (which over time will reduce even further as contact wear occurs) and should the switch become wet (a very high chance) the XLR-4 male socket will go to Mains potential.I know that this method of switching would unlikely comply for electrical safety in Australia but what about the rest of the world? The lamp is a product from Italy.I do not want to be held responsible for this kind of setup, safety-wise because I believe it is electrically unsafe however i need some genuine evidence to back up my concern. It might be that this is perfectly OK. It might be thought that the switch is not designed to pass both DC and AC and different times because of the eventual wear to contact sets is out of spec ... something like that .Anything would be great.

author: vk6zgo
author_rank: Super Contributor
timestamp: October 04, 2017, 11:18:17 pm
content: Well, I probably wouldn't do it that way, but as such a switch is commonly used to breakboth sidesof the 230v Mains, the insulation between the two sides should be much better than " a few microns", otherwise, equipment would be shorting the Mains out & going up in smoke every day.Maybe you could fit a better rated switch just to be sure, or to be doubly sure, switch the 12 volts supply separately.The News Crew would probably bitch about the latter approach, but it would ease your mind.

author: Tomorokoshi
author_rank: Super Contributor
timestamp: October 04, 2017, 11:35:02 pm
content: 1. One thing is a little unclear. Is the 12 V connection for switching the 12 VDC, or is it for the illumination in the switch?2. Are there specific safety standards listed for the device? Either on the box or in the manual?3. Is it meant for use outside of a regular office environment?4. What is the expectation of isolation between AC and the 12V output? For instance, in the past perhaps such a lighting fixture used 240 VAC incandescent lamps where someone wouldn't be in contact with them anyway.5. How much current is available to the 12 VDC load? I can't figure out the DC current rating of it from the datasheet.

author: thm_w
author_rank: Super Contributor
timestamp: October 04, 2017, 11:48:19 pm
content: I think we need some pictures of inside the switch to know what you are talking about.It is UL rated for 250VAC so I would be surprised if there is a lack of clearance between any of the 4 connections. Other than between the 2 LED connections, in the case of 12VDC of course.

author: vk6zgo
author_rank: Super Contributor
timestamp: October 04, 2017, 11:55:57 pm
content: Quote from: Tomorokoshi on October 04, 2017, 11:35:02 pmI think the point is, that such switches are usually used to breakboth sidesof the Mains, so the insulation must be good enough that the Active & Neutral cannot be connected to each other at any time, as that would be a direct short on the incoming 230v supply.As this doesn't commonly happen, if the switch is 250v rated, as the specs indicate, the OP's concern about its internal clearances is misplaced.Whether it is a good idea to share a switch like that is another question, altogether.It could be dangerous to someone working on the device who may assume that if one side of the switch is, say, +12volts DC, the other side would be the DC common.Alternately , they may think that the DPST switch means both sides of the Mains are Isolated when it is OFF,so----not a good idea!!

author: Phoenix
author_rank: Frequent Contributor
timestamp: October 05, 2017, 12:34:40 am
content: Quote from: vk6zgo on October 04, 2017, 11:55:57 pmJust because a switch has functional or basic isolation rating for 250V (single point of failure) doesn't mean it will comply with double/reinforced (redundant against single failure) requirements. Particularly when he says there is likely water involved!

author: jbb
author_rank: Super Contributor
timestamp: October 05, 2017, 12:43:28 am
content: You could try contacting the OEM with this specific question. They may be able to help.If, in the end, you determine it's unsafe, you could fit a relay to power on the 12V output.

author: Muttley Snickers
author_rank: Unknown
timestamp: October 05, 2017, 12:59:16 am
content: When mains double pole switching is utilised such as in mobile caravans and similar sites the user would be somewhat protected where the active and neutral are connected through the upstream RCD, MCB or ELCB device. The application described by the OP would probably not incorporate any safety aspect between the LV and SELV services so should the AC mains feed to the switch come adrift and it happened make contact with the DC side where the end user may be less cautious then a potentially dangerous hazard could result.

author: peteb2
author_rank: Regular Contributor
timestamp: October 05, 2017, 01:59:19 am
content: These pictures should explain how this appliance has been wired.The black pair on the switch are for Mains Active while the red are for the external +12V supply. My concern: a switch failure etc could see Mains Active on the Vdc input connector...

author: Richard Crowley
author_rank: Super Contributor
timestamp: October 05, 2017, 03:02:42 am
content: Your interior photos show MUCH BETTER than average design and construction (compared to your average lighting fixture). Since the switch is rated for far higher than the voltage differential that you are concerned about, I agree with @vk6zgo that your concern is misplaced.A lamp with open vents like that is NOT intended to be used in the rain, etc. So your concerns about getting wet would apply to everything else in use besides the lamp. This is why we now have warning labels that say: "Do not use toaster in bathtub." If the people using it are that stupid, they shouldn't be allowed anywhere near the gear.Move along, there is nothing to see here.

author: Someone
author_rank: Super Contributor
timestamp: October 05, 2017, 03:54:51 am
content: The switch would need to be inspected to see if there is sufficient clearance+creepage internally between the contacts, hard to say without looking further into it. If thats the mains flex wired through a terminal block you've got plenty more problems to fix to meet the appliance wiring rules.

author: Someone
author_rank: Super Contributor
timestamp: October 05, 2017, 03:56:25 am
content: Quote from: Richard Crowley on October 05, 2017, 03:02:42 amYou say its neat and tidy, I'd say its a long way from meeting international safety standards.

author: Richard Crowley
author_rank: Super Contributor
timestamp: October 05, 2017, 06:20:28 am
content: Quote from: Someone on October 05, 2017, 03:56:25 amIf you have worked on many theatrical/production light fixtures, you would note that this is much neater and cleaner than most of the genre. To be sure, it is rather at the inexpensive end of the scale. Certainly not Arri or Mole-Richardson, or even Lowell, et.al. But for an inexpensive lighting fixture it appears to be above average compared to what I typically see. Certainly it is built to a price-point. But it is far from the dangerous design that peteb2 is imagining. That switch manufacturer claims approval certification from practically everyone you have heard of around the planet.

author: tautech
author_rank: Super Contributor
timestamp: October 05, 2017, 06:39:41 am
content: Quote from: Someone on October 05, 2017, 03:56:25 amI wouldn't be so sure.Consider a slightly larger 3PST switch, maybe switching 3 phases.What matters then is the dielectric strength/spec between poles.We use DPDT switches for switching transformer taps for example without a second thought.If a suitably spec'ed switch was chosen for the OP's application there should be no concern but the wiring colours chosen for mains and 12V in this thing are totally another thing.

author: vk6zgo
author_rank: Super Contributor
timestamp: October 05, 2017, 07:43:16 am
content: Quote from: Someone on October 05, 2017, 03:54:51 amA Mains rated switch is unlikely to rely upon clearance+ creepage to isolate the two halves when it is easy to provide a moulded barrier between the two poles.The screw in feed through probably clamps the Mains flex.I suppose it should use crimped spade lugs like on the switch, instead of the terminal block, but thousands of such connections have managed to operate safely over decades without killing people.I dunno about the appliance wiring rules ----- some delights slip through, like the toaster with an SPST switch in the Neutral line, & one side of the Mains (Active in this case), connected to the frame holding the heater element, which can easily be accidentally touched, from the top of the thing.Brush against the top of the supposedly "off" "appliance" whilst reaching for something , & then pick yourself up off the floor!

author: amyk
author_rank: Super Contributor
timestamp: October 05, 2017, 10:40:38 am
content: There is a septum between the two poles in all the ones I've opened up.

author: jolshefsky
author_rank: Regular Contributor
timestamp: October 05, 2017, 12:29:48 pm
content: The easy way to make it right is to have two switches: one for the AC power and one for the 12V. But that makes the user interface more complex so I bet that's why they went with this. Safety doesn't come from "very unlikely but plausible" but from "implausibly unlikely." It's plausible that under not-so-unusual circumstances that condensation or an insect could get into the single switch providing a path from mains to the 12V—low-current indeed, but high enough to kill. With two switches, unless the unit is downright wet and used without a GCFI (which, assuming safe practices, you'd not have non-GCFI and wet in the same place), there is no such danger.

author: stj
author_rank: Super Contributor
timestamp: October 05, 2017, 02:30:20 pm
content: Quote from: tautech on October 05, 2017, 06:39:41 amthat's the u.s. for you - American stupid black & white coding.

author: mikerj
author_rank: Super Contributor
timestamp: October 05, 2017, 02:43:13 pm
content: Quote from: jolshefsky on October 05, 2017, 12:29:48 pmWonder what happens if you hook up 230v AND 12v together...

author: rs20
author_rank: Super Contributor
timestamp: October 05, 2017, 02:45:17 pm
content: Quote from: vk6zgo on October 04, 2017, 11:55:57 pmThis logic seemsdangerouslyinvalid, assuming the 12V DC is mains earth referenced. For example, Class X capacitors must have insulation good enough to withstand line-to-neutral, so by your logic, Class X capacitors are totally fine for line-to-ground usage as well. As anyone who knowsthe difference between Class X and Class Y capacitorsknows, this is in fact completely unacceptable reasoning.Even if there's no direct analogy for self-healing dielectrics in physical switches, it all boils down to probability of failure multiplied by risk of fire (line-to-neutral) vsdeathby electrocution (line-to-earth).Now is this switch "Class Y"? Probably, I dunno, ask the manufacturer. But just pointing out that it's "Class X" is hopelessly insufficient.

author: Someone
author_rank: Super Contributor
timestamp: October 05, 2017, 09:22:22 pm
content: Quote from: vk6zgo on October 05, 2017, 07:43:16 amYes, as suggested internally there is likely a fin or wall between the two contact sets but without disassembling the switch its not possible to say its 100% ok. The terminal block in the earthing connection is just the start of the wiring problems and does not meet AS/NZS basic electrical safety requirements.Quote from: Richard Crowley on October 05, 2017, 06:20:28 amIt is entertaining when people jump to conclusions about others experience, I've worked on a wide range of luminaries/instruments/lights/lanterns/(whatever the term you wish to use) including those in installations dating from the days of manual dimmers predating semiconductors. Times change and what met electrical safety standards (or lack there of) in the past are no longer safe to use in a professional setting unless they are rebuilt to modern expectations, also note the substantial difference in risk between our 240V (now 230V) regions and those with 110V supplies.

author: vk6zgo
author_rank: Super Contributor
timestamp: October 06, 2017, 05:45:28 am
content: Quote from: rs20 on October 05, 2017, 02:45:17 pmIt isn't any type of capacitor, so Class X & Class Y does not apply.A closer analogy is whether the insulation between Active & Neutral in a power cord is any different to that between Active & Earth.

author: Monkeh
author_rank: Super Contributor
timestamp: October 06, 2017, 09:45:04 am
content: Quote from: Someone on October 05, 2017, 09:22:22 pmOh no, an extra joint, we're all doomed!Sorry, but that I just find that quite amusing.. I know it's not quite optimal, but if you can trust one screw terminal you can trust 20 of them (and already do).Quote from: vk6zgo on October 06, 2017, 05:45:28 amNo, it really isn't. If you have a CPC in a cable, itisconnected to earth, or at least it should be. A class Y cap, on the other hand, doesnotneed to be connected to earth, and can be connected to exposed metalwork which is not earthed. Ask any Macbook owner about that.This is exactly the same issue as the creepage and clearance on an SMPS - is there adequate clearance between components of two isolated systems or not?

author: Siwastaja
author_rank: Super Contributor
timestamp: October 06, 2017, 10:20:22 am
content: Depending on actual switch construction and specs, either a real safety concern, or not. It may have required creepage, but I doubt so. Most likely doesn't conform to the regulations, but might not be far off; the actual level of danger can be only evaluated by looking at the actual switch.I guess the gap is much more than "microns"; more likely 1-2mm, with some plastic inbetween.In any case, not super serious due to low probability of failure; much more serious safety issues do widely exist (such as: using random caps instead of Y caps; or using creepages way below 0.5mm between L and safety isolated side).The probability is low because, as explained above, the switch in its most typical usage casemustbe rated to withstand AC live-to-neutral voltage between the legs, and AFAIK, incidents of these kind of switches arcing over between L&N are extremely rare.Hence, most likely, it won't ever happen that the 230V side would accidentally arc with the 12V side.This being said, if not specifically specified so, this does not conform to regulations, and for a good reason: the L&N arcing is considerably less serious incident, as it "only" causes a fire hazard, most likely handled by upstream fuses & fire retardants in plastics - the analogue of X caps is the right one. Whereas, when used like the OP describes, L to safety isolated side (12V) connection doesn't give any signs of failure to anyone, and creates a very real death trap by electrocution situation.So, in all regulations, L-to-safety-isolated-side has much more strict requirements than L-to-N.So while the chances of a failure are extremely low, the consequences are much, much more severe than what happens when the same type of switch fails in its intended way of usage.

author: amyk
author_rank: Super Contributor
timestamp: October 06, 2017, 10:58:49 am
content: This is a 12V automotive switch. Observe the septum between the two contact chambers, which is present despite it being SPDT since this is a common mould. The ones in the 250VAC switches I've seen are even deeper. It would have to be a pretty catastrophic failure for the two sides to short together.

author: Someone
author_rank: Super Contributor
timestamp: October 06, 2017, 11:03:19 am
content: Quote from: Monkeh on October 06, 2017, 09:45:04 amIts both not optimal and fails compliance of more than one national standard, whats so funny about that? Putting such a connection inside a product with extreme temperature cycling in service is an extremely poor design even without a specific requirement prohibiting it. Or should we all ignore the legal requirements we are expected to meet and just use whatever some person said on the internet should be ok?There are very specific requirements for electrical safety that vary wildly from country to country and product class to product class, navigating them and producing a product thats complaint worldwide is time consuming and expensive and beyond the reach of most small businesses. This small photo of one part of the product has numerous failures to the applicable NZS rules and would fail on similar clauses in other countries. While the OP came here worried about the switch they too missed the elephant in the room of that unacceptable wiring.

author: Monkeh
author_rank: Super Contributor
timestamp: October 06, 2017, 11:56:34 am
content: Quote from: Someone on October 06, 2017, 11:03:19 amThe fact that it's quite possibly less of a concern than the switch.QuoteIs there actually extreme cycling? I don't know.QuoteNever said that.QuoteIs it unacceptable? Does it really deal with temperature cycles extreme enough to be a problem? Is the cable meant to be replacable, and how do you allow for that if you go straight into a crimped lug?And in all this concern over the probably safe but almost certainly non-compliant switch, and the possibly non-compliant but also probably not evil screw terminal, nobody has noticed the most likely point of failure: A gland is not a cable clamp.

author: Someone
author_rank: Super Contributor
timestamp: October 06, 2017, 12:20:52 pm
content: Quote from: Monkeh on October 06, 2017, 11:56:34 amThe switch might be compliant, the terminal block might be complaint to pass the earth through, but the wiring arrangement isn't, no way no how.Quote from: Monkeh on October 06, 2017, 11:56:34 amIts a luminaire, with big heatsinking visible in the photo. It will have large thermal cycling.Quote from: Monkeh on October 06, 2017, 11:56:34 amThe gland might meet the pull out requirements and doesnt appear to fail any abrasion/wear requirements, again, this requires testing to confirm its applicability like the switch. But the wiring its clearly unable to meet the segregation requirements particularly with regard to the accessible contacts on the socket that the OP raised. Overall its unlikely to be worth the time to meet compliance and would be cheaper to reject the design and find alternatives.

author: rs20
author_rank: Super Contributor
timestamp: October 06, 2017, 12:30:11 pm
content: Quote from: vk6zgo on October 06, 2017, 05:45:28 amYourlogicwas that anything that's safe between live and neutral must also be safe between live and earth. Yourlogiccan be therefore used to "prove" that Class X caps are fine for Class Y applications. Class X caps are absolutely NOT fine for Class Y applications, so therefore yourlogicis refuted, regardless of whether you choose to apply it to capacitors, switches, or PCB clearances + creepages. There's no analogies here at all, just dangerously wrong logic.Besides, the insulation in a power cord is "Class Y" (as in, safe to use between live and earth), and it correctly follows that it's also "Class X" (as in, safe to use between live and neutral). This is absolutely the opposite to you starting with the observation that the switch is safe to use between live and neutral, and concluding that it's safe to use between live and earth. So no, a power cord is a farworse, completely backwards analogy.Safe between live and earth implies safe between live and neutral.Safe between live and neutral DOES NOT imply safe between live and earth.

author: dmills
author_rank: Super Contributor
timestamp: October 06, 2017, 06:32:19 pm
content: It is worth remembering that the electrics grips are experienced and trained in this stuff, they are at least in theory 'competent persons', and as such are not 'the public', I cannot get too excited about that luminaire. If it can run of 12V from a smallish connector, it is NOT going to run notably hot, the power level is just not there.Given some of the on set shennanigans that I have seen electrics grips get up to, that stuff is the least of the problems.I give you the wonder that is the Camlock connector (Single pole, 400 or 800A), often used for three phase generator hookup and sometimes made up with the male on both ends....For reference a normal sort of tungsten production lighting unit from Arri or such starts at 500W and goes up from there rapidly, no way is that toy pulling anything like that, so it clearly cannot run that warm (Case temperatures on a reasonably serious production lighting unit can cook bacon and eggs, as I think Big Clive has demonstrated at least once)....I am seeing sleeving providing substantial double insulation in there, and that terminal block is actually a good idea (For all that I might have preferred a ceramic one), these things get fixed in the field and the presence of that connector means the earth will likely be reconnected rather then being loosely clamped under a mounting screw somewhere (at best)....Could it be better, well, yea, probably, but it is a LONG way from tripping my alarms and I would be quite happy to take that thing on set.Regards, Dan.

author: SeanB
author_rank: Super Contributor
timestamp: October 07, 2017, 04:44:13 am
content: Approved lighting fittings will have a similar connector block in them for power inlet, and the only thing different is here there will be a small captive plastic insulator sheet under the connector block, providing both reinforced insulation over the existing powder coat paint on the sheet metal, along with a wiring diagram showing line, neutral and earth connections for use. Only issue I find with those is the earth connection is a pressed tag in the case, used to hold the terminal block in, and then the earth connection relies on the connector block screw biting through the paint to connect to it. That almost always works, but the contact area is small.Yes the use of the switch might be poor, but 3 pole switches are not as common, and many international specs allow single pole switching, some allow double pole switching and some prohibit switching the neutral, all YMMV. I worry more about somebody replacing that switch when it fails, using the illuminated version, with the 90V neon lamp and the 120-180k 1/8W carbon film resistor ( with it's 150VDC rating) inside, connected from one side to the other. I find that those double pole switches tend to fail with age, though most of them are well made contact side, the thin plastic rocker has issues at the pivot points and wears, or the translucent versions crack with age.

author: vk6zgo
author_rank: Super Contributor
timestamp: October 07, 2017, 09:50:55 am
content: Quote from: rs20 on October 06, 2017, 12:30:11 pmFirstly, you are putting words in my mouth.Nowhere did I state that you can use an "X" rated capacitor in place of a "Y"rated one.You extrapolated from the case of EMI suppression capacitors to that of insulation in general.Your confidence in using the same terms caused me to suspect that I had missed a significant development in the use of terminology.On Googling for "X & Y ratings for other than capacitors", all I found were references to capacitors.Several other permutations returned a similar result!Capacitors are a special case, as their "insulation" consists of very thin layers of dielectric, so they are vulnerable to breakdown where the insulation barrier in a switch will probably consist of several mm of PVC or similar material.Switch manufacturers are most unlikely to produce a "dumbed down" version of insulation because "a short circuit between Active & Neutral apparently doesn't matter!"All that said, I did say that it isn't the way I would do it.My point about the insulation is still valid.

author: wraper
author_rank: Unknown
timestamp: October 07, 2017, 10:08:58 am
content: Quote from: vk6zgo on October 07, 2017, 09:50:55 amYou make me facepalm really. X and Y caps is completely valid analogy for insulation requirement difference between live conductors and live to something than can be touched by person.

author: wraper
author_rank: Unknown
timestamp: October 07, 2017, 10:26:30 am
content: The same as on above picture applies to the switches. Between the switch terminals requirement is to prevent fire (analogy to X capacitor). Between the switch terminals and chassis requirement is to prevent electric shock (analogy to Y capacitor). FYI when high current is switched, some amount of metal contacts is evaporated because of arching, that can cause thin conductive film build up inside the switch which in long term may cause conductive path between the contact groups in the switch. If it happens between live wires, this thin conductive film will just evaporate once short happens and high current flows through it. If part of the switch is used on the low voltage side, it may cause electric shock.

author: vk6zgo
author_rank: Super Contributor
timestamp: October 07, 2017, 10:46:10 am
content: I honestly couldn't bother arguing any more.'Bye

author: Siwastaja
author_rank: Super Contributor
timestamp: October 07, 2017, 02:22:33 pm
content: wraper,IMO the problem with analogies is that, while they are extremely powerful for some, there always are people who don't understand the very concept of what an "analogy" actually is -- or even if they superficially know, still have issues in really understanding them.The most prominent example of this is the so called "Hitler card" or "Godwin's law" phenomenon: no matter how good an analogy someone makes using Hitler (theoretically a very good subject for analogy, since his (simplified) traits are very well known and agreed on), several people totally fail to understand what it means to use an "analogy", and start panicking among these lines: "Oh, the Hitler card is here, now the discussion is over!", or "do you compare that toHitler?"To rephrase, your analogy was just fine and actually quite a good one. It isn't 1:1, but analogies never are. Otherwise, they wouldn't be called analogies, they would be, umm, equal things?I have mostly stopped using analogies because I find about 10% of people totally failing to understand any analogy, or even the concept thereof, on a deep level, and for some reason, these people never say "sorry, didn't quite get it, could you explaing more carefully?", but instead go into the aggressive arguing mode.For some reason, safety-related threads often end up being a train wreck like this, since people get emotional and stop thinking.

author: vk6zgo
author_rank: Super Contributor
timestamp: October 08, 2017, 01:24:23 am
content: Quote from: Siwastaja on October 07, 2017, 02:22:33 pmI wasn't going to continue in this thread, as I have been laid up with the 'flu, & didn't feel up to it, but feeling a bit better, & finding others "piling on" has provoked me to return for just one more.In the beginning, I made a comment, & was happy to leave it at that.rs20, & thenwraperleapt in " in aggressive arguing mode", the former with red type & underlining (looks pretty emotional to me).QuoteI understand analogies, but my point was always that they were inappropriate in this case, as the insulation requirements for switches arenot" If it breaks down" it won't cause electrocution",they are"The insulation is such, that, under any reasonably foreseeable circumstance, it will not break down if used within its ratings"The makers of X & Y capacitors specify how they will be used , & advise they should not be used otherwise.Switch makers don't have that luxury.Certainly, there is a difference between the insulation between both poles & the outside world, & that of pole to pole, but that is due to the construction of the device as much as safety concerns.The silly thing is thatrs20could have argued his case effectively without the analogy, but that wouldn't have given him the opportunity to be pompous!This is only anecdotal, but in 40 plus years in Electronics, mostly working with high power transmitters, I can't recall seeing a switch which had broken down pole to pole.I've seen lots cooked by current overloads, or by arcing, or others with plain old mechanical failure( in my experience, the most common fault).

author: rs20
author_rank: Super Contributor
timestamp: October 08, 2017, 03:27:38 am
content: I'm sorry if I've caused offence, all I'm trying to point out is the following:Safe between live and earth implies safe between live and neutral.Safe between live and neutral DOES NOT imply safe between live and earth.Given that this principle extends to clearances and creepages on PCB layouts, it seems (at leasta priori) like a not-at-all unreasonable stretch to suggest that it applies to switches as well. Thus, simply observing that a switch is considered safe for use between live and neutral isinsufficientto conclude that it is safe between live and earth.You appear to have other information to hand which leads you to believe that switches are safe for both uses; if this is the case, the correct response for you to make is "ah yes, sorry, I used a bad argument there. But my end conclusion is correct, because <insert alternative argument here>". What's extremely puzzling to me is that you instead doubled down on defending the original argument. I think Siwastaja has a point in that providing the capacitor example contributed to this; although I am disappointed that my attempt to provide a simple, illustrative example was so misinterpreted.It's important to distinguish arguments from conclusions. There can be incorrect/flawed arguments (e.g. "Safe between live and neutral implies safe between live and earth") that lead to a correct conclusion (ostensibly, "Switches are safe to use between live and earth"). An attack of the former is not necessarily an attack of the latter, and neither is an attack on the person putting forward the argument.

author: wraper
author_rank: Unknown
timestamp: October 08, 2017, 11:21:04 am
content: Quote from: vk6zgo on October 08, 2017, 01:24:23 amIMO this is not true at all. X and Y capacitors are not necessarily used exactly for mains filtering, many of them have DC rating. Switches must be used according to their spec as well, say if there is no DC rating, switch is not suitable for DC.

author: Siwastaja
author_rank: Super Contributor
timestamp: October 08, 2017, 01:27:20 pm
content: Switches do have the specs, safety standards, agency approvals etc. just like X & Y caps. This is normal everyday engineering.If a certain switch doesn't have these specs, it's a telltale sign that the switch most likely won't conform to the safety regulations; at least the designer has more homework to do, and the liability shifts.In the usage case like this, the switch of course needs to have a specification for isolation / creepage between the two halves and it must match what the legislation expects from isolation between live and safety isolated side, which is the class of highest requirements in everyday electronics, considerably higher what is required between live and neutral.If the spec doesn't exist or is below the level required by the legislation, then the company using the switch need to do their own in-house testing & paperwork.

author: wraper
author_rank: Unknown
timestamp: October 08, 2017, 02:41:54 pm
content: Quote from: Siwastaja on October 08, 2017, 01:27:20 pmThis still would be very questionable. Manufacturer can change internal construction at any moment without affecting rated specifications. But this could change not rated isolation below safe value.

author: mikerj
author_rank: Super Contributor
timestamp: October 09, 2017, 12:30:23 pm
content: Quote from: wraper on October 07, 2017, 10:08:58 amI see where you are coming from, but it's really quite a poor analogy. The basic construction of capacitors means they are quite vulnerable to breakdown by transient voltages, and the breakdown could be permanent unless steps are taken to prevent it, i.e. self healing dielectric, which is why special capacitors are required for line voltages.The switch in question will have a very large safety factor built in at its rated voltage, the chances of breakdown between either the poles or between one pole and the chassis it's clipped into are literally negligible.

author: Siwastaja
author_rank: Super Contributor
timestamp: October 09, 2017, 12:52:57 pm
content: Quote from: mikerj on October 09, 2017, 12:30:23 pmWill it? That'sexactlywe are trying to discuss here, but speculation won't give a definite answer.There are all kind of switches with different amount of air & plastic inbetween.Nice that you are so sure about a random switch, without the spec sheet specifying anything about this clearly.Yes, it probably does have enough clearance & creepage, or at least enough to be safe "in practice", even if not completely up to regulations, but pure guesses are not ok from the legislation viewpoint. You need data whether it exceeds the minimum required or not. Simple as that.It's the same with caps... They are not intrinsically safe, or unsafe. But of course there's the difference that a safe Y cap is much more difficult to design and manufacture than a switch, since you cannot just use extremely large distances because you can't get the capacitance then. So you need special control in materials.

author: wraper
author_rank: Unknown
timestamp: October 09, 2017, 01:22:33 pm
content: Quote from: mikerj on October 09, 2017, 12:30:23 pmWhy are you so sure? If you compare datasheets for Y capacitors and 250V AC switches, you'll notice there is barely any advantage for switches in this regard even for contact - case insulation. Insulation between contact groups usually is not specified separately, only dielectric breakdown voltage between contacts is specified. Not to say, unlike in Y capacitors, switches experience arching when switching which can greatly reduce breakdown voltage at that moment. Also unlike capacitors, switches can easily accumulate moisture inside them due to open construction.

author: amyk
author_rank: Super Contributor
timestamp: October 09, 2017, 03:55:00 pm
content: Look at the picture of the switch I posted and then ask yourself how it could be constructed without the septum and not short across the poles if given some slight vibration.The construction essentially guarantees there's going to be separation.

author: wraper
author_rank: Unknown
timestamp: October 09, 2017, 04:33:00 pm
content: Quote from: amyk on October 09, 2017, 03:55:00 pmWho said there necessarily will be mechanical short? Also, do you assume every switch is equal? What if thin separation breaks if someone smashes the switch? Will it work fine most of the times? Yes. Will it bite you in the ass (give electric shock to someone) one in a millionth of times? Probably. And in such case the only responsible people will be idiots who designed and accepted this. Remember Samsung Note 7 with their batteries. Only very rare failed, yet damage to the company was extreme.

author: sean0118
author_rank: Frequent Contributor
timestamp: October 11, 2017, 12:33:29 pm
content: Not only does the earth input go to a terminal block, but it's also shorter than the active and neutral, ensuring that it is the first to break if the strain relief fails.

author: peteb2
author_rank: Regular Contributor
timestamp: December 15, 2017, 08:34:06 am
content: OK everyone as the OP i have give a final report upon what had to happen. Based on the fact that there was a possibility that the way 12Vdc and Line of 230Vac was being switched on the same switch (and the fact the PINS of the XLR-4 male socket could be easily touched, then it was decided to mod each light.The fact i'd noticed a questionable situation of a possible safety issue kind of follows under the Laws in this Country that i needed to do something to circumvent any chance of an accident resulting in an electrocution. I could have zipped the whole unit back up and put it out to be used by my fellow staff, ( the camera News Crews at the station i'm employed at as a Qualified Registered Maint Engineer) but under OSH and new Health & Safety rules let alone the Govt. section of the Electrical Workers Registration Board, if anythingactuallyhappened i'd become a "port of call" in an inquiry for sure.So the Mains is now not permanently attached but connectable via a Neutrik mains plug/socket... PowerCon series connector. The original switch breaks L and A only. The Earth off the Powercon connect goes directly to chassis via a crimped spade terminal and held under a wrinkle shakeproof washer with a 3mm screw and nut. The XLR-4 connector with the 12Vdc now has it's own dc switch in the +ve line.The cost to doing the mod if properly charged and each minute of labour checked would send a company accountant to DRINK !The only reason it was done is to comply with the incredibly strict considerations of this country's current newly applied Health and Safety Act of which all businesses are taking the option of we'd best do "X" or else....Thanks for all the input from all who took time to post....

author: CopperCone
author_rank: Super Contributor
timestamp: December 16, 2017, 05:31:37 pm
content: its bullshit, the OEM wont know shit unless its breaking. Most people dont know what the fuck is going on in a switch. Its a complicated electromechanical problem, relies alot on plating too.I would consider it a no no

author: mikerj
author_rank: Super Contributor
timestamp: December 16, 2017, 06:18:45 pm
content: Quote from: wraper on October 09, 2017, 04:33:00 pmMany of us have heard or, or experienced a Class X cap failing (RIFA), but how many have had a double pole rocker switch fail shorted, or even arc between the poles when used at it's nominal rating? It has to be a spectacularly rare event, if it has happened at all.If someone smashes the switch then they could directly expose the live connection, a far more serious problem than possible short to the other pole, so that's another irrelevancy. As previously mentioned, this isn't even a consumer device.

author: tpowell1830
author_rank: Frequent Contributor
timestamp: December 16, 2017, 06:28:26 pm
content: Quote from: peteb2 on December 15, 2017, 08:34:06 amOkay, have been listening to the arguments about whether this is true or that is true, but what sticks out is the original question, and I paraphrase: "Is this configuration safe?"My answer would simply be "I don't know because I do not have ample information about this system, other than a picture."With that said, the thought that I have about changing a design of electrical wiring and components in a device that will be used and handled by humans is that, if I change that design and modify the wiring and/or components, the liability of failure now falls on me.My solution would be to replace all of the units with an acceptable unit that has been checked for all of the above safety concerns. This way, the safety questions and concerns are met and I have not refocused the liability on myself or my team.Just my 2 cents...

author: CopperCone
author_rank: Super Contributor
timestamp: December 16, 2017, 09:17:15 pm
content: I saw fucked up rocker switches (from DC) on an entire product line!

author: vk6zgo
author_rank: Super Contributor
timestamp: December 17, 2017, 12:26:49 am
content: Quote from: tpowell1830 on December 16, 2017, 06:28:26 pmYou obviously have never worked in a TV Studio!When Production people want stuff, they "want it yesterday"!!Virtually all this sort of stuff comes from "the other side of the world", made by manufacturers who "take their own good time" about things, so most times, if there is a problem the only practical thing is to fix it locally.

author: rs20
author_rank: Super Contributor
timestamp: December 17, 2017, 04:49:35 am
content: Quote from: tpowell1830 on December 16, 2017, 06:28:26 pmThis is a question of safety, so "I don't know" automatically translates to "no" for all intents and purposes.The reason the debate has run so long on what seems like a simple question is because it's actually a dangerously vague question which hides two specific, easily answerable questions:- "Is it acceptable to do this/does the manufacturer guarantee that this is acceptable?"- "Is it reasonable to expect that harm couldn'ttypicallybe done?"The answer to the first question is fairly clearly "no", and plenty of reasonable evidence that the answer to the second is "yes" has been provided.What's disturbing to me is that people have been answering the second question as if it's a valid answer to the first. Such an attitude shows a severe disrespect for human life, and I hope it's not coming from practicing engineers. Safety is not a field where you get to speculate on what's "almost certainly" true.

author: Gregg
author_rank: Super Contributor
timestamp: December 17, 2017, 06:56:47 am
content: There seems to be lots of room in the fixture to replace the existing switch with a standard industrial 22mm switch. They come in multiple configurations like 2 position or 3 position and the actual switching modules come in NO and NC. Multiple switching modules can be stacked making your circuits totally isolated on a single switch.

author: SeanB
author_rank: Super Contributor
timestamp: December 17, 2017, 11:06:29 am
content: Quote from: mikerj on December 16, 2017, 06:18:45 pmThose switches regularly fail, and I have had them blow up as well when moisture provides a bridge, or the little springs inside decide to break and the floaty bits short out the 2 sides. The plastic also degrades with time, and as the inner side often is made from recycled or mixed content ( the bits that were either rejects repelletised, or the recycled plastic of mixed colour from some random seller) as it is not visible. Stove repairers are very well aware of how poor these switches are, they are a common failure on many things, either popping the top off exposing the live inner parts, or simply shorting, or even just falling apart with time. Hard to tell the quality unless you have a well known manufacturers unit, and that could be replaced by anybody with a non correct part for either cost cutting, or as a service part, without anybody being the wiser, as the cutout and pin outs are a common industrial size.I agree on the use of a 22.5mm industrial control panel button and using some industrial contact assemblies, as those are both robust, double acting fail safe contacts and each module is isolated from each other to withstand 2.5kV for 30 seconds insulation test, just place 4 blocks so the wear is kept the same, even if one block is never going to be used, and so that the mains section is separated physically from the 12V side by a barrier strip.