EEVblog Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: intabits on July 12, 2018, 10:38:47 am
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Yesterday I received a strong electric shock, of the most dangerous kind - through both arms and the chest area. (posted here as it's a "catch-all" category)
I was using my variac contraption to test a new dummy load project, and had both switches on it turned off as I was adjusting the position of the variac and the load. I was holding the variac handle with one hand, but a finger on the other hand touched a wire on the dummy load when I got the boot.
Most fortunately, the RCD that I had fitted to the variac contraption tripped and saved me.
The neutral coming out off the variac was live, so the three switches in the active line (two of which were off) did nothing to prevent the danger. I probed around and tested things, including the IEC cable going into the variac, but somehow got it confused with a good one and missed the actual fault until after I had torn open the variac looking for a wiring mistake. Finally I found the fault in one of the IEC cables, shown below.
(https://www.eevblog.com/forum/projects/whats-wrong-with-this-picture-the-iec-cable-that-nearly-killed-me/?action=dlattach;attach=474644;image)
The incoming active on the three prong plug, connects to the neutral of the IEC plug!!
I've discovered that Argentina uses a similar 3 prong plug to the Australia/New Zealand type, but with reversed active and neutral pins. Maybe this thing came from Argentina? I have no idea where I got it. It's also a bit of a sloppy fit into the IEC socket, and doesn't feel like its making a positive connection.
I don't yet know if it's related to this fault, but the cable also has a sharp bump on the plug, not very visible in the photo, but circled here:-
(https://www.eevblog.com/forum/projects/whats-wrong-with-this-picture-the-iec-cable-that-nearly-killed-me/?action=dlattach;attach=474650;image)
The "output enable" switch on my variac is a DPST, but I have both poles in parallel for current handling, switching the active. I think I might rewire it to switch both active and neutral instead. That way I can be sure the output socket is safe, no matter what fault precedes it.
The variac contraption, also described in this thread:-
https://www.eevblog.com/forum/projects/a-simple-project-to-enhance-a-variac-with-a-voltagecurrentpowerenergy-meter/msg1358361/#msg1358361 (https://www.eevblog.com/forum/projects/a-simple-project-to-enhance-a-variac-with-a-voltagecurrentpowerenergy-meter/msg1358361/#msg1358361)
(https://www.eevblog.com/forum/projects/whats-wrong-with-this-picture-the-iec-cable-that-nearly-killed-me/?action=dlattach;attach=474656;image)
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The "output enable" switch on my variac is a DPST, but I have both poles in parallel for current handling, switching the active. I think I might rewire it to switch both active and neutral instead. That way I can be sure the output socket is safe, no matter what fault precedes it.
Sounds wise :-+
I've noticed powerpoints being wired the wrong way around quite a few times both here and overseas, it's not worth trusting neutral vs active. Best to assume both are hot.
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Have you ever seen a European Schuko plug - https://en.wikipedia.org/wiki/Schuko
Two side earth contacts and two pins for live/line and neutral, and reversible, so the "neutral" at 220v and "live" around earth potential issue occurs 50% of the time all the time.
john
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One should consider both wires as potentially hot. There is a chance that the neutral return wire might be disconnected somewhere and thus power through another consumer.
I don't know the NZ plugs, but there might be another problem: the ground pins also looks to be sleeved. At least with the UK plugs this is a problem, as the ground contact might be to far up the pin.
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This is why you have isolation transformers. Trusting the electrician or the cable for correct polarity is the certain way to get harmed.
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I wouldn't trust an ordinary DPST toggle switch for isolation. If one of the contacts welds, the usual over-center spring mechanism used for such switches will *NOT* prevent the toggle actuator moving to the off position, with no indication the load circuit is still live.
Either fit a proper safety isolator switch or remember to *ALWAYS* physically disconnect the supply or load before touching any part of the load circuit.
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I've discovered that Argentina uses a similar 3 prong plug to the Australia/New Zealand type, but with reversed active and neutral pins. Maybe this thing came from Argentina? I have no idea where I got it.
It seems to be the case. I'm almost sure it didn't come from Arg but I guess this cable was meant to be sold in our market. Everything comes from China now. IRAM 2073 norm defines neutral on the left if the earth pin is upwards. We usually don't care to plug things backwards also.
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The real problem here is your assumption about neutral being safe, never do that - and especially not on devices connected with detachable connection to power grid.
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The real problem here is your assumption about neutral being safe, never do that - and especially not on devices connected with detachable connection to power grid.
THIS. Do not confuse neutral and PE, they are two totally and completely different things.
You should be able to assume PE as being safe. It always isn't, but the incidents are fairly rare, and close to an actual purposeful manslaughter.
However, in relatively large part of the world - most of the Europe, for example! - the live and neutral are totally interchangeable, and both are and always should be treated as "live". Even though some countries do offer polarized plugs, the risk is still too big to take.
You can say the cable is trying to kill you when it has live or neutral connected to "PE". But it appears this is not the case here, at all.
The fact that the OP hasn't understood such basic concept of the mains and is blaming the cable is very alarming. Please learn the basics and take care.
You have basically poked around live mains all the time without realizing it. You were hit now for the first time, but didn't realize the reason why it happened. Yes, neutral is live. Yes, just learn this.
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However, in relatively large part of the world - most of the Europe, for example! - the live and neutral are totally interchangeable, and both are and always should be treated as "live". Even though some countries do offer polarized plugs, the risk is still too big to take.
The fact that the OP hasn't understood such basic concept of the mains and is blaming the cable is very alarming. Please learn the basics and take care.
It's the same in Latin America. You never know which is live until you check it out. I guess op knows what is doing but he took for granted that IEC cable wasn't inversed and this took him by surprise. We can argue about good or bad practices for decades.
You can say the cable is trying to kill you when it has live or neutral connected to "PE". But it appears this is not the case here, at all.
If I find a cable like this I would be looking for where to hang someone from the tallest tree.
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I really don't get why people assume there is a neutral on a specific side of the connector. Even with connectors that can only be plugged in one way you can't make that assumption unless you have done all the wiring yourself or at least checked it...
It's much easier to just assume you don't know which is which and treat both pins as hot.
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[...Best to assume both are hot.
I normally would assume that also, but I know that my house is wired properly.
One mistake was assuming that a manufactured molded cable would be wired correctly.
But I take the point made by the replies here that my other mistake was not fully isolating both power wires before handling the connected device.
I wouldn't trust an ordinary DPST toggle switch for isolation. ... fit a proper safety isolator switch
I will look into a isolator switch for this, but that would mean a rebuild.
As well as the RCD, the box has a standard DIN mount double pole circuit breaker.
I imagine that they do not suffer from the fault mode you described?
Do you know if such circuit breakers are designed to also be used simply as regularly operated switches?, ie: can it be used as an isolator switch?
Meanwhile I'll rewire both DPST switches to switch both live and neutral, and continue my usual practice of switching them both off when not in use.
They are large switches with screw terminals, I'll check the rating, but I doubt that current handling would be a problem anyway.
I normally would physically disconnect before intentionally touching the load, it was an accidental touch.
Of course, intent is irrelevant when you're dead...
If I do rebuild the variac box, maybe it should include some sort of a "neutral fault" alarm.
In any case, I will be checking active/neutral polarity much more often in the future.
The real problem here is your assumption about neutral being safe, never do that...
I do know that a fault can render neutral unsafe, (boy, do I know!) and that it's far better to switch both rather than active alone.
The fact that the OP hasn't understood such basic concept of the mains and is blaming the cable is very alarming. Please learn the basics and take care.
I do understand the basics. And that cable *is* faulty, not as bad as live and earth swapped, but still wrong. I'm sure it would be illegal to sell here in Aus.
Yes, I did make the mistake of not unplugging and/or fully isolating both active and neutral lines before handling connected devices, and nearly paid dearly for it.
At least I made the non-mistake of fitting an RCD, and I'm thankful for that.
To all posters: I know it is wrong to assume that neutral is safe. And despite that, I've been guilty of doing so.
The main purpose of my post is to alert people to the fact that manufactured cables that are intended to be polarized may sometimes be polarized incorrectly (for any given locale)
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Have you ever seen a European Schuko plug - https://en.wikipedia.org/wiki/Schuko
Two side earth contacts and two pins for live/line and neutral, and reversible, so the "neutral" at 220v and "live" around earth potential issue occurs 50% of the time all the time.
That's not even plug related tbh. There were (and still is not in many countries, I'd guess majority) no laws saying which side of socket should get L and which N (just recommendations and best practices) so you can't ever assume it is wired correctly (well, most of the time it will be, but there are always some shitty installations, or just bad electricians).
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I wouldn't trust an ordinary DPST toggle switch for isolation. ... fit a proper safety isolator switch
I will look into a isolator switch for this, but that would mean a rebuild.
As well as the RCD, the box has a standard DIN mount double pole circuit breaker.
I imagine that they do not suffer from the fault mode you described?
Do you know if such circuit breakers are designed to also be used simply as regularly operated switches?, ie: can it be used as an isolator switch?
Circuit breakers and isolating switches in a similar DIN mount form factor are designed so that the actuator cannot move fully to the Off position unless the contacts are actually open. If provision is made to gang them via a pin through their actuators for multi-pole use, or they are multipole with a single actuator, they cant fail partially On without it being obvious that the actuator is part-way.
A double pole circuit breaker that has the holes to retain a lockout/tagout device to prevent its actuator being moved to 'On' is usable as an isolator but may have a very limited operating life as its not intended for frequent use as a switch. The life may further be reduced by switching it under load.
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In Greece (I guess in other countries also), both holes on a wall socket are equally dangerous. A plug can be inserted either way.
Alexander.
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I always consider both sides to be live conductors, even if you know your house is wired correctly, assumptions can be lethal as illustrated here. I have seen wiring mistakes on a number of occasions, not to mention with 240V circuits in this part of the world both conductors *are* live. Never assume, just as you would never point a gun at someone even if you know it isn't loaded, never touch exposed wiring that is connected to a source even if you know it's not supposed to be live. In some parts of the world polarized plugs are not really a thing, so I would not assume all power cords to be wired correctly. Even when they are supposed to be, mistakes can happen.
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If you pull out the plug then you can be very sure that the device is disconnected!
Switches can fail or just get bumped. Turn them off, then unplug it.
I once accidentally switched on a 3kv supply when I moved it to reach around to the back to check the connections. Some idiot had also used a banana plug with exposed metal. Now I unplug things.
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Good to pull the plug. Here in the US I use one of those little $5 LED testers to confirm outlets are wired correctly. More importantly, I use it to confirm my many power strips are wired correctly and not floating.
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You should be able to assume PE as being safe. It always isn't, but the incidents are fairly rare, and close to an actual purposeful manslaughter.
Some years ago I was working on some equipment and decided to connect the PE connection. Did so, plugged it in and touched the metal chassis and got a belt. After a lot of investigation, I found the whole building had been miswired and the PE connection was connected to the building line connection.
A nice cheap socket tester is now in my tool box.
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My house is one of those split level designs that was very popular in the 60s-70s, often sold as a starter home with an unfinished basement. The idea being you buy the house and live upstairs, then later when you can afford it you finish the downstairs to your liking. It's a nice concept, but the issue is you see widely varying quality of workmanship with the downstairs, in my case every switch was installed on the neutral side, the cheapest of cheap hardware was used and the wires were cut off just long enough to be inserted into those hideous push-in terminals as the receptacles and switches were pushed into the box, rather than properly accordion-folding the wire with at least 6" past the box opening as code requires. I had to redo all of it and pigtail the receptacles since the wires were cut off so short. I did this after I made the careless assumption that turning off the switch would cut the power to a light fixture and got a shock from it. I now try to never assume.
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While this may be an incorrect cord, my own personal standards for working with or designing line (mains) connected devices are that any time a human (myself included) comes in direct contact with conductors that are not isolated from the live/neutral supply wires, a fundamental mistake has been made and it's time to turn stuff off and think about what I've done, even if no shock was incurred. :)
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Even if all was wired properly, you would still receive electric shock through the load if neutral wire lost the contact. Poking around anything live with more than one hand and/or touching something conductive with any body part is just asking for Darwin award.
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I had to redo all of it and pigtail the receptacles since the wires were cut off so short.
I don't feel alone anymore :-DD I've redone almost every electric circuits in every house that I've lived in. I've found things like telephone lines sharing conducts with 220V wires, strangled or broken conducts, audio cables instead of copper wires and so on. This summer I replaced the main panel and installed a PE rod. I had to install also a secondary panel to control 3 water pumps with a 24V contactor and a motor breaker for each pump. Floating switches inside water tanks were carrying 220V in the previous circuit. As I'm a little bit paranoid I always do a double or triple check to be sure that all breakers are always off and not conducting anything.
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I don't feel alone anymore :-DD I've redone almost every electric circuits in every house that I've lived in.
How about this?
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How about this?
It hurts my eyes...
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There is certainly some crazy stuff out there, some of the pictures from other countries that have or had more lax regulations or just more DIY types and more very old structures show some really... creative work.
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The incoming active on the three prong plug, connects to the neutral of the IEC plug!!
Perhaps I'm being particularly dense today, but doesn't your picture show continuity between the two live connectors anyway?
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Either fit a proper safety isolator switch or remember to *ALWAYS* physically disconnect the supply or load before touching any part of the load circuit.
This is a good habit to follow. Always do it this way.
At times it may seem unnecessary. But when you're tired, or under time pressure, or the equipment/wiring is faulty, or some moron changes your setup without telling you, and you simply act out of habit, this habit will save your life.
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Although I do like polarised sockets and think they're much safer, than pot luck as to which conductor is phase and neutral, one should never assume the neutral conductor is at earth potential. Always treat the neutral, as if it were live!
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The incoming active on the three prong plug, connects to the neutral of the IEC plug!!
Perhaps I'm being particularly dense today, but doesn't your picture show continuity between the two live connectors anyway?
I don't think so. The IEC plug should have the same pin arrangement as the wall plug -- imagine it's nothing more than an extension lead. Doing anything different would require "re-arranging" the wires in the bundle or the connectors, which makes little sense.
Your bottom diagram might be using one of those creative definitions of 'male' and 'female' that consider the plastic rather than the pins. Or visa versa. I always get it wrong reading those, don't ask about SMA and RP-SMA too :D
For similar reasons I dislike datasheets that show transistor pinouts from an orthographic view, but don't label which one. Top or bottom? Front or back? "Oh, you're just supposed to assume that under *standard*".
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The incoming active on the three prong plug, connects to the neutral of the IEC plug!!
Perhaps I'm being particularly dense today, but doesn't your picture show continuity between the two live connectors anyway?
I don't think so. The IEC plug should have the same pin arrangement as the wall plug -- imagine it's nothing more than an extension lead. Doing anything different would require "re-arranging" the wires in the bundle or the connectors, which makes little sense.
It does though. If you rotate both ends so earth is up, active is on the left on both ends.
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I don't think so. The IEC plug should have the same pin arrangement as the wall plug -- imagine it's nothing more than an extension lead. Doing anything different would require "re-arranging" the wires in the bundle or the connectors, which makes little sense.
Nope. The pinout of IEC 60320 C13 & C14 connectors is *supposed* to be well defined*, with the C13 trailing female connector or outlet connector, wide side down, face view, being NGL and the C14 inlet or plug, wide side down, pin view, being LGN. The pin order in the wall socket is dependent on your national electrical wiring standards, so the cord may need to cross over the L and N wires to maintain the correct order. Various countries in the EU with sockets compatible with the Schuko CEE 7/7 plug are particularly problematic as their sockets are non-polarised, but the Shuko CEE 7/7 plug itself *does* have a defined polarity as it fits French CEE 7/5 polarised sockets.
There is additional confusion when dealing with non-technical people as they tend to call anything on the end of a cord that fits into a fixed connector a 'plug' even if it has female contacts and call a chassis mount recessed connector with male contacts a 'socket'.
* However, you'll have a hard time finding the pinout in any official IEC document that isn't behind a paywall, and its equally difficult to find a reputable manufacturer of IEC C13 & C14 connectors that actually gives a wiring diagram for their product
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Just to reply to myself, I just got a chance to measure some of my cables and active comes out on the right if earth is up. Backwards to what I expected, but shows OP has a point I suppose.
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I called it a "plug" because it goes inside a receptacle, even though its pins are female.
It's not visible in the photos, but the molding has L,N & E markings, and the resistor is inserted into the one marked "N"
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* However, you'll have a hard time finding the pinout in any official IEC document that isn't behind a paywall, and its equally difficult to find a reputable manufacturer of IEC C13 & C14 connectors that actually gives a wiring diagram for their product
https://www.bulgin.com/media/bulgin/data/PX0587-587SE-597Wiring.pdf (https://www.bulgin.com/media/bulgin/data/PX0587-587SE-597Wiring.pdf)
Difficult?
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That diagram is no help resolving the general C13 & C14 pinout problem unless you have a Bulgin PX0587, PX0588 or PX0597 connector physically in front of you or a high-res photo of one open, etc. as there is absolutely nothing to indicate whether the wiring view is with the wide side up or with it down. I just cant understand why Bulgin and their competitors don't show the pinout on the face or pin view of their mechanical drawings.
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I don't think so. The IEC plug should have the same pin arrangement as the wall plug -- imagine it's nothing more than an extension lead. Doing anything different would require "re-arranging" the wires in the bundle or the connectors, which makes little sense.
That doesn't make sense. The IEC plug is used worldwide, with the other end of the cable having whatever plugs are used locally. The only way you could have a straight-through arrangement is if there was a worldwide standard of which side live/neutral are on. The standard NEMA-15 receptacle in the US puts neutral on the left when ground is at the bottom, I don't know about foreign standards but I would not assume them to be the same other than by coincidence.
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I don't think so. The IEC plug should have the same pin arrangement as the wall plug -- imagine it's nothing more than an extension lead. Doing anything different would require "re-arranging" the wires in the bundle or the connectors, which makes little sense.
That doesn't make sense. The IEC plug is used worldwide, with the other end of the cable having whatever plugs are used locally. The only way you could have a straight-through arrangement is if there was a worldwide standard of which side live/neutral are on. The standard NEMA-15 receptacle in the US puts neutral on the left when ground is at the bottom, I don't know about foreign standards but I would not assume them to be the same other than by coincidence.
Oh wow. I didn't think of the wall sockets also being re-arranged.
... do international plug adapters re-arrange the A & N? Given some of them are "multi-standard" I presume this can't be done reliably.
Then there's also the issue of dog-leg 240V, where both the A & N are hot.
Any hope of either wire in a C13/C14 being reliably neutral, even if it was when I tested yesterday, is now gone in my mind ;D
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That diagram is no help resolving the general C13 & C14 pinout problem unless you have a Bulgin PX0587, PX0588 or PX0597 connector physically in front of you or a high-res photo of one open, etc. as there is absolutely nothing to indicate whether the wiring view is with the wide side up or with it down. I just cant understand why Bulgin and their competitors don't show the pinout on the face or pin view of their mechanical drawings.
It's.. pretty obvious it's a top down view.
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That's not even plug related tbh. There were (and still is not in many countries, I'd guess majority) no laws saying which side of socket should get L and which N (just recommendations and best practices) so you can't ever assume it is wired correctly (well, most of the time it will be, but there are always some shitty installations, or just bad electricians).
There generally is no "correctly" when it comes to schuko. That's what many people unfamiliar with the standard seem to struggle with. There is no presumption of what is a right and wrong side as it's all fully reversible, so accidents with installations where phase and neutral are swapped can't occur. As long as ground is in the right place you're basically good, avoiding the dangerous assumptions and badly followed standards of polarised sockets.
That being said, there are various sockets and plugs being used and not all play nice.
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One should consider both wires as potentially hot. There is a chance that the neutral return wire might be disconnected somewhere and thus power through another consumer.
I don't know the NZ plugs, but there might be another problem: the ground pins also looks to be sleeved. At least with the UK plugs this is a problem, as the ground contact might be to far up the pin.
This ^^
I have not read the entire thread, but can confirm that NZ/AU plugs are NOT meant to have sleeving on the earth pin, so you have a poorly made and non-compliant cable in more ways than one. The sleeving-on-PE thing can be very dangerous, but given it'd be more effort than just leaving it bare it boggles my mind as to why the shady manufacturers keep doing this.
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As some have already mentioned I also disconnect the cable from mains when working on mains devices.
I have the rule that I must keep the disconnected plug in my viewsight before I start working on the device; and never just unplug it and leave it near the socket, I leave it "far apart" from it.
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I have not read the entire thread, but can confirm that NZ/AU plugs are NOT meant to have sleeving on the earth pin, so you have a poorly made and non-compliant cable in more ways than one. The sleeving-on-PE thing can be very dangerous, but given it'd be more effort than just leaving it bare it boggles my mind as to why the shady manufacturers keep doing this.
Likely ignorance, it's not hard to believe that a lot of people out there don't understand the purpose of the sleeving and figure if it's good to have it on two of the prongs then it's better to have it on all three. The sleeved prongs are quite a nice feature which I had never seen until I encountered British plugs. A nice design overall aside from being so bulky, but anything is a compromise.
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The sleeving works best on british plugs - the pins are so massive that a nice thick insulator can be added without reducing strength by any noticeable amount.
On NZ/AU plugs either the sleeving is pretty thin (and thus fragile, I've had it crack off when using those multi-country adaptors with shutters that end up applying pressure to the sides of the pins) or the pin gets narrowed and loses some strength.
The sleeving requirement can of course be eliminated by designing the socket with a recess for the plug (e.g. Shuko and other continental European types).
As for working on mains equipment, I either have the plug out and where I can see it, or when that is impossible I stick a meter in there to measure neutral&live->PE voltages before and after the switches are turned off (so that I can be sure it's both wired correctly and is fully off).
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The sleeving works best on british plugs - the pins are so massive that a nice thick insulator can be added without reducing strength by any noticeable amount.
On NZ/AU plugs either the sleeving is pretty thin (and thus fragile, I've had it crack off when using those multi-country adaptors with shutters that end up applying pressure to the sides of the pins) or the pin gets narrowed and loses some strength.
The sleeving requirement can of course be eliminated by designing the socket with a recess for the plug (e.g. Shuko and other continental European types).
As for working on mains equipment, I either have the plug out and where I can see it, or when that is impossible I stick a meter in there to measure neutral&live->PE voltages before and after the switches are turned off (so that I can be sure it's both wired correctly and is fully off).
There are also plugs that have the "sleeve" be part of the plastic body and quite hard and sturdy, rather than a thin layer added later.
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Good to pull the plug.
Yes, so easy to do, and no chance of dodgy mains wiring giving you a bad day.
Here in the US I use one of those little $5 LED testers to confirm outlets are wired correctly. More importantly, I use it to confirm my many power strips are wired correctly and not floating.
I have 2 neon panel lights wired on L-E and N-E on the output socket of my variac. Provides a quick visual check that all is OK.
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When it comes to power sockets and cables, everyone except practicing electricians is dyslexic. Having a standard in place is easy. Trusting it is a pipe dream.
I will always use DPST switch when possible to interrupt both lines. Not to parallel up on one and leave the the other constantly connected. Even the cheapest of chinese import goods/tools I've bought which run directly off mains without a transformer have this setup on the power switch. I think maybe it's part of being "double insulated?"
I have some reversed power cables from Chinese T12 irons. When I discovered it, my first thought was to throw them out. Then my second thought was... it doesn't change anything as far as I'm concerned. I suppose the fuse should go on the live side, if possible. That's about it. I mean, I discovered the problem, because it must have "mattered" to what I was doing, at the time (honestly can't remember). But not in any way that would have shocked me. I don't trust myself to know which is live or neutral, let alone whoever wired my house or supplied my IEC cable. :)
The ubiquity of the reversible figure 8 non-grounded cord/connector is proof this live/neutral thing was never more than a "looks good on paper" kind of bureaucratic achievement.
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Yesterday I received a strong electric shock, of the most dangerous kind - through both arms and the chest area. (posted here as it's a "catch-all" category)
I was using my variac contraption to test a new dummy load project, and had both switches on it turned off as I was adjusting the position of the variac and the load. I was holding the variac handle with one hand, but a finger on the other hand touched a wire on the dummy load when I got the boot.
Most fortunately, the RCD that I had fitted to the variac contraption tripped and saved me.
The neutral coming out off the variac was live...
This kind of crap is all too common.
This is exactly the reason why hospital-grade power cords in Canada must have transparent plastic molded ends so that anyone can see what wire goes to what pin of the connector. And all of the wires must be different colours: black, white, green/yellow.
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This is exactly the reason why hospital-grade power cords in Canada must have transparent plastic molded ends so that anyone can see what wire goes to what pin of the connector. And all of the wires must be different colours: black, white, green/yellow.
I use transparent ends when I reterminate older power cords, or when I make short US-to-AU conversion leads, for the same reason: to allow visual inspection.
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I cut open that cable, and it had the internal blue/brown colours wired correctly to the IEC end, but wrong for the AU plug end.
They were also pretty piddly conductors, I doubt anything like the 10A stated on the plug - binned the lot.
I'm thinking of adding a feature to the variac to catch swapped active & neutral wires.
A lowish voltage MOV, say around 60-120V, in series with a 5W resistor such that 240V would cause 100-200mA to flow, and connected between Neutral and Earth, after the RCD.
Then if neutral were live, the RCD would trip. Worth doing? Are there any possible issues that I'm not seeing?
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I'm from Argentina, we don't make plug cords as far as I know, all of the ones I've seen are from CN or came with some product from somewhere else, so probably we are all using the wrong wiring in many many places, also the wall outlets are all miss-wired so in some cases it comes back good. Only newer, installations are getting better but even then many electricians don't mind to cross the leads when they make wiring with opposed outlets, meaning one of them is always wrong. the best I can do is when I have a spare pole in the power switch I switch both incoming lines. We have a death every few years for electric shocks, but being 40M people and so other stuff wrong I don't thing this is the main cause. We use a 30mA GFCI for the whole domestic installation, but not everybody has it installed, that's worse than a crossed hot and neutral. When is a leak and the GFCI trips and they can't find the leak they cross the wires for the whole house so if it was a correctly wired outlet it isn't anymore. And I can keep going...
Long story short, in the lab use an insulation transformer even with the variac (before it) and always switch both hot and neutral or just unplug the thing. You are intentionally touching the damn wires most of the time, safety measurements are for normal use failures, not for someone poking inside, that's why there's a sign only the things saying open at your own risk or electric hazard inside, or whatever...
JS
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This is why you have isolation transformers. Trusting the electrician or the cable for correct polarity is the certain way to get harmed.
But an isolation transformer makes it impossible for an RCD to do its job, and the RCD is what cut the power and saved the day.
An isolation transformer allows you to connect any single point of the circuit to earth ground, and when you do so, you don't get a shock, and power is not interrupted. After that first connection is made, if you touch a different point in the circuit while touching ground, you can get a shock, and nothing will stop it. In other words, you get to make one mistake without suffering harm, but the second mistake can be a serious problem.
If you use an RCD without an isolation transformer, as soon as you connect any part of the circuit to ground, either directly or through a resistance (the human body being a resistance for the purpose of this discussion), the power is immediately cut off. In other words, the first mistake cuts the power, so you don't have an opportunity to make a second mistake.
Both strategies have their advantages and disadvantages. Both strategies require reasonably care, and reasonably correct wiring procedures. Both will protect against one single mistake. Neither will protect against a case where a person contacts both sides of a circuit simultaneously, appearing to be a load.
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Yes, we are all living in a death trap. Even ground can go live at home, if the neutral is broken.
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I cut open that cable, and it had the internal blue/brown colours wired correctly to the IEC end, but wrong for the AU plug end.
They were also pretty piddly conductors, I doubt anything like the 10A stated on the plug - binned the lot.
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Are there any possible issues that I'm not seeing?
If the faulty cord has an AU approval number, then the approval should be revoked and the product recalled:
https://austest.com.au/au-nz-approvals/ (https://austest.com.au/au-nz-approvals/)
https://www.fairtrading.nsw.gov.au/buying-products-and-services/product-and-service-safety/electrical-safety/safety-labels-for-electrical-goods (https://www.fairtrading.nsw.gov.au/buying-products-and-services/product-and-service-safety/electrical-safety/safety-labels-for-electrical-goods)
From the second link:
The approval mark should be permanently on the article itself – being on the box or container is not sufficient. If you cannot see an approval number or mark on a declared article, ask the salesperson to show you the approval number. If they can't show it to you, don't buy it. If you find a store selling electrical articles that have no approval numbers or markings, contact NSW Fair Trading. We are responsible for monitoring the safety of electrical goods sold in NSW.
See the second link for the formats of approval numbers.
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The incoming active on the three prong plug, connects to the neutral of the IEC plug!!
Perhaps I'm being particularly dense today, but doesn't your picture show continuity between the two live connectors anyway?
I don't think so. The IEC plug should have the same pin arrangement as the wall plug -- imagine it's nothing more than an extension lead. Doing anything different would require "re-arranging" the wires in the bundle or the connectors, which makes little sense.
Your bottom diagram might be using one of those creative definitions of 'male' and 'female' that consider the plastic rather than the pins. Or visa versa. I always get it wrong reading those, don't ask about SMA and RP-SMA too :D
For similar reasons I dislike datasheets that show transistor pinouts from an orthographic view, but don't label which one. Top or bottom? Front or back? "Oh, you're just supposed to assume that under *standard*".
Regarding the gender of connectors: it doesn’t matter which side is in your hand and which is fixed, or whether a plastic part gets inserted into another. What matters is the mating surfaces. The ones which are pins or otherwise stuck out are male. The ones that are holes are female. The key thing being that it’s only the mating surfaces that are considered. So the cord in the OP has a male Australian plug on one end and a female IEC plug on the other.
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Regarding the gender of connectors: it doesn’t matter which side is in your hand and which is fixed, or whether a plastic part gets inserted into another. What matters is the mating surfaces. The ones which are pins or otherwise stuck out are male. The ones that are holes are female. The key thing being that it’s only the mating surfaces that are considered. So the cord in the OP has a male Australian plug on one end and a female IEC plug on the other.
I've come across the opposite before. Mating surfaces are male (pins) but the outer plastic connector was "female"; so they named it female.
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Regarding the gender of connectors: it doesn’t matter which side is in your hand and which is fixed, or whether a plastic part gets inserted into another. What matters is the mating surfaces. The ones which are pins or otherwise stuck out are male. The ones that are holes are female. The key thing being that it’s only the mating surfaces that are considered. So the cord in the OP has a male Australian plug on one end and a female IEC plug on the other.
I've come across the opposite before. Mating surfaces are male (pins) but the outer plastic connector was "female"; so they named it female.
Yes, you see that usage in the wild sometimes, but they’re mistaken. There is a convention, and it’s not that! ;)
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As others have said, treat both N and P as 'live' wires.
Its best not to try and figure out which is N and which is P unless you have a need to know this info, like if you're adding a fuse or wiring up a plug. Otherwise just think of it as two hot wires.
The worst thing you can ever do is think to yourself
"hm.. that's ok, this neutral wire is earthed at the fuse box, so it's safe"