What's wrong with this picture? The IEC cable that nearly killed me

[intabits]

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.


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:-


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

 

[Whales]

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.

[johnkenyon]

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

[Kleinstein]

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.

[Benta]

This is why you have isolation transformers. Trusting the electrician or the cable for correct polarity is the certain way to get harmed.

[Ian.M]

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.

[HoracioDos]

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.

[kony]

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.

[Siwastaja]

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.

[HoracioDos]

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.

[agehall]

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.

[intabits]

[...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)

 

[xani]

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).

[Ian.M]

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.

[firewalker]

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.

[james_s]

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.

[donmr]

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.

[Conrad Hoffman]

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.

[Neilm]

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.

[james_s]

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.

[mmagin]

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.

[wraper]

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.

[HoracioDos]

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 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.

[wraper]

I don't feel alone anymore I've redone almost every electric circuits in every house that I've lived in.

How about this?

[HoracioDos]

How about this?

It hurts my eyes...