The Cable That Should Not Be

The other day, all of my UPSes started beeping.

This did not surprise me. I live in Katoomba, New South Wales, and mains power is a little flaky up here. That's why I've got so many UPSes, plus a vintage big-ass power conditioner I bought cheap on eBay - it's currently sitting on a shelf, but will no doubt come in terribly handy Real Soon Now.

What was odd this time was that the mains power was, as the UPSes were telling me, off. But the lights were still on.

That, obviously, meant that a breaker or RCD or something had tripped in the house's fuse box.

So I went out there, and observed that everything was fine. Breakers all on, master switch on, giant safety-wired council fuses still intact.

(Which fact I, of course, discovered by cutting off the safety wire and levering the big porcelain fuse blocks out with my pocket knife, while wondering whether I'd actually manage to jump all the way over the fence if this obvious suicide attempt came to fruition. My feet weren't bare, it wasn't raining, and the lid of the breaker box stayed up by itself so I didn't have to balance it on the top of my head, but this was otherwise as silly-looking a thing as I've ever done while standing in front of a breaker box.)

Lighting circuit and its spinning-disc usage meter: Working fine. Power circuit and its separate meter (a clue!): Dead as a stone.

Long story short, I called an electrician, and while he was glumly inspecting the Edwardian-era wiring on the back of the breaker panel, a nice lady came down the street to ask whether there was a blackout.

For lo, her house had no power at all.

At this point, both of us highly technical manly men twigged to the fact that this house has two separate power feeds coming to it from the pole outside. Those two feeds are from two of the three phases carried by the pole. One of those phases, the one that feeds the house's power circuit, had dropped out. The phase feeding the lighting circuit was still up.

Three-phase power uses three separate live conductors, each of which carries an AC waveform 120 degrees out of phase with either of the others. Various commercial and industrial premises have a full three-phase hookup; three-phase is useful for driving some kinds of high powered motors. It's perfectly normal for street mains wiring to be three-phase too, but ordinary houses only need single-phase power. So, usually, each house in a street is hooked up to one of the three available phases.

But for some reason, some ordinary houses get more than one.

If one phase is knocked out on the average street, therefore, only the houses hooked up to that phase will go dark. That's likely to mean about one third of them. This odd-sounding situation is actually quite common, though people often don't notice, because they don't walk up and down the street to see if everybody's lost power when their own lights have gone out.

In my house's case, loss of one phase gives me a two-thirds chance of losing lights or power, but no chance of losing them both.

The power cut lasted a few hours, long enough that I started to worry about the food in the fridge. Plus, I wanted to eat some of the food in the fridge, but opening the fridge door during a blackout is not a great idea. Unpowered fridges can stay cold for quite a long time, but not if you open the door.

I, accordingly, made this.

Power Cord Of Mystery

On the other end of this magnificently wrong-looking object (hey, it could be worse) is the refrigerator. Which ran fine from light-socket power for the, oh, ten minutes or so before the bloody power came back on anyway and I plugged the fridge back into the wall.

Connectors seldom seen together

In the olden days when mains electricity was a new idea, getting the 'lectricity on meant you had light sockets installed, and nothing else. Wall sockets were rare, because there wasn't much you could plug into them. If you wanted to run some appliance other than a light, you just plugged it into a light socket, using a cable that terminated in an Edison screw or bayonet plug.

If you hack the plug end off an extension cord, it takes only a couple of minutes to replace it with a light-socket plug, which you should be able to buy from any decent hardware store. That's what I did.

The very existence of light bulb connector plugs invites you to do this sort of thing, which could explain why their packaging (here in Australia, at least) is printed with dire imprecations against fooling with this stuff if you are not a qualified electrician.

Which I, gentle reader, am not.

The warnings are not kidding. There are several entertainingly dangerous ways in which a cord like this can go wrong.

The only contacts available in a light socket are active and neutral. So you can't, in this case, make a cable that creates a circuit from active to earth (which will instantly trip an RCD "safety switch") or neutral to earth (which will probably also trip the RCD, in a slightly more roundabout way, if anything else is running on the same circuit at the same time). You certainly can, however, make a cable that swaps active and neutral. Indeed, it's impossible not to if your cable terminates in a bayonet connector - you can plug those things in either way around.

Reversing active and neutral is a land-mine of a mistake. It can sit there harmlessly for years, and then interact with another individually innocuous mistake to kill yo' ass dead.

The lack of an earth also means... there's no earth. Whatever I plug in via my magical mystery light socket extension cable will now be un-grounded.

This, also, is generally harmless. Completely harmless, if whatever I plug into the cable isn't grounded in the first place (look for "double insulated" on the appliance label, or just a two-pin plug).

But the primary purpose of earthing is to protect you from being zapped by a faulty appliance. If you plug, say, a shiny chrome toaster into an ungrounded cable (which you probably shouldn't do anyway; a light bulb socket will become warmly unhappy if you ask it to run a thousand-watt toaster), and a live wire comes loose inside the toaster and touches the chassis, then the toaster will sit there with a live chassis and wait for you to touch it.

(It'd be great if you could be touching the sink with your other hand when you do that, by the way. Thanks.)

If the toaster's earth wire is connected, the above failure will trip an RCD in milliseconds, or blow a fuse/trip a circuit breaker in only slightly more time. With no earth wire, the small load created by a dying human body will not bother your house's breaker box at all.

The way to make a cord like this safe is, therefore, to terminate it with a two pin plug, so you physically can't plug an earthed appliance into it.

(If you want to get really fancy, you can give it an inline fuse too, to prevent it from overstretching the socket it's plugged into. A reader's now also pointed out to me that you could put an RCD/GFI/ALCI/WTF-protected outlet on the end of such a cable. "Safety switches" do not actually need an earth connection - they detect earth leakage, to the proper circuit earth or anything else, by looking for a difference in the current flow through the active and neutral conductors. If there's a difference, the extra current must be going somewhere, that somewhere may be bad, and so the safety switch trips.)

Here in Australia, I don't think there's any such thing as a two pin extension cord. Or a separate two pin in-line socket, for that matter. You could achieve the same result by blocking a three-pin socket's earth hole with glue or something, though.

This safe version of the cable would, of course, be much less useful than the unsafe version. I couldn't have plugged the fridge into a socket with a blocked earth pin. Well, not without busting the earth pin off the fridge plug, anyway.

(Do people ever do that? Of course they do! What better way could there possibly be to get rid of an earth loop?! [PDF])

So I shall leave this cable in its unsafe state. It'll lurk, like the poisonous snake that it is, in our electrical-junk cupboard, waiting for the next time half the house goes dead.

With any luck, no further deaths will result.

21 Responses to “The Cable That Should Not Be”

  1. Stark Says:

    You know it is a realtively trivial amount of work to wire in a proper wall socket where there was once an unused light socket.... I actually have a similar situation to you - except I have full 3 phase to my breaker since the previous owner apparently had some hefty arc welding equipment. It didn't take me long to wire an additinal wall socket (well, 3 of them to be exact) to take advantage of the situation. Power is usually pretty reliable here but the off phase outlets have come in handy once or twice. I also bought a MIG welder... but alas it only uses mundane single phase 220 so my solitary 3 phase plug still goes unused.

    I realized as I was writing this that I don't acutally know for certain that a new socket is possible for you - here in California it is a trivial thing but thats because all house wiring (by code) has all three wires - active, neutral and ground. Even though the lights don't use the ground it is there to be used should you want to. I'm not sure about the electrical code for Katoomba... ;)

  2. richard Says:

    Speaking of dangerous iring, when I was in Peru, I found all the portable electric water heaters dangerously wired. These are little heaters that affix to the shower head and heat the water as it passes through.

    Being a tall fellow, I kept touching the shower head (the average Peruvian is shorter than I am) and getting shocked. Eventually, I just crouched and showered.

    Hmmm ... I don't suppose you have considered some alternative power sources - like some nice zero point energy source, or, failing that a few wind turbines on the roof?

  3. Sonictail Says:

    Hey, you're not dead and you got food by using ingenunity, I hope that meal tasted good. And i'll be honest, I never thought about my home wiring that way.

  4. evilspoons Says:

    I had exactly the same thing happen in my house. I live in Canada where we have 120V mains, but we get two 120V phases coming into the house in order to run 240V appliances such as the oven and dryer.

    After my dad spent a rather... intense... half an hour replacing the master breaker (which, if done wrong, can lead to Horrible Death), we switched it on and... tada... still half the house didn't work. Apparently someone had managed to run a backhoe through one of the three phases, one of which was connected to half of my house. D'oh.

  5. bmorey Says:

    I've had a similar experience. A few months back the F&P washing machine starting beeping furiously and wouldn't start. House lights and PC running OK. Called F&P and put in a service call.

    In meantime twigged what the problem was. House has 3-phase 440 volt power for the airconditioner. One phase was out. Rang supplier - they investigated and repair the fault. Washing machine now OK and cancelled service.

  6. bmorey Says:

    As an addendum to the light-socket power fitting I can remember when you could get these as a double-header. Run the iron and a bar heater off the one light socket!

  7. Daniel Rutter Says:

    On the subject of light bulb multi-adapters - all hail Big Clive!

  8. matt Says:

    Here in Germany, it's pretty standard to have three-phase wired into the house, and it's not unusual to have house-hold appliances which expect to have all three (ovens, for example, but also plenty of home workshop-type motorised gear).

    Normal single-phase sockets here (16A!) also don't provide any way of establishing polarity, but this isn't seen as much of a problem.

    One issue with this is when changing a light-bulb in a desk-light. No bayonet-cap light-bulbs here - they're all screw-in, so a reversed connection makes the base of the light-fitting live. Putting a finger into a light-fitting is a stupid thing to do anyway, but can happen, especially in the dark! Even nastier if the light in question doesn't have a double-pole switch - someone might think the light is switched off, but live power can still be present on the shell of the light fitting.

    What I do like about these plugs is that they're recessed. An australian plug can hang half-way out of a socket in such a way that the electrodes are visible and live, and the electrode is accessible to small fingers or metallic objects - this can't happen with these sockets.

  9. Daniel Rutter Says:

    Matt: Actually, modern Australian plugs are required to have partially shrouded active and neutral pins, to avoid exactly the problem you mention. About the first half of those two pins must be covered with insulation. If the plug comes out a bit, only the insulated portion can be touched by J. Random Conductor poked down between plug and wall.

    The insulation always seems to be black - you can see it on the pins of the plug in this picture, for instance.

    There are lots of other kinds of mains plug that've had this sort of requirement for quite a while, of course.

  10. Orpheus Says:

    In the early days of retail electricity, the light sockets were charged at a cheaper rate than the general-use electricity. That's one of the reasons why so many appliances came with light-socket plugs instead of the wall version.

    The worst electrical safety thing I've seen personally was at a kebab joint. Way up on top of their drinks fridges, buried in the grease, was a four-socket power board with no plug - just two bare wires, which were poked into the active and neutral (the wrong way round...) of the socket end of an extension cord. The grease had built up to the point where it was actually bridging the two stripped wire ends and occasionally tripping the fuse, blacking out their drinks fridges.

  11. magetoo Says:

    matt: I was thinking along the exact same lines, namely "WTF does he mean reversing active and neutral? There's stuff that expect a difference?".

    I lived in Ireland for a short while, and it seemed to be pretty common for people in the funny-language-tech-support community to hack their own adapters so they could plug in their own European hardware. I have seen some reasonable hacks; and I have seen people just forcing their plugs into extension cords and using a spoon jammed into the ground hole to get it all to work. (Something needs to be plugged in there to basically open a switch.)

    It seems this wouldn't be that bad (if done right), but if it is possible to "kill yo' ass dead" by reversing the wires, I wouldn't want to be in the opposite situation, plugging in UK/AU appliances into a European socket.

    So matt, Dan; is it actually common having things that expect active and neutral to be in their correct places in countries that provide for a distinction? Because that scares me a little.

  12. matt Says:

    Dan, good to know that newer Aussie plugs have this shrouding.

    I haven't lived in Oz for a while now - guess it's fair enough that some things have changed in the meantime. ;)

  13. matt Says:

    magetoo, to be honest, the case I mentioned above (light fitting) is about the only one that springs to mind as dangerous, and empty light fittings are dangerous anyway...

    Other devices which only have single-pole power switches may unexpectedly have live power in them if connected the wrong way around, but that should normally only be of concern to people who poke around inside them. :) I can imagine situations where always having a high potential on an electronic component might have some unexpected side-effects, but what would I know.

    Some european countries have polarised domestic plugs and sockets, some don't. I have no idea what the regulations are for devices sold in the EU, but that probably shouldn't make any difference to how you work with equipment - if you assume that any exposed electrical conductor is live until proven otherwise, then you'll stay alive. :)

    I can't imagine any electrical device being wired so badly that an unexpectedly reversed AC polarity would cause the case of a device to be live, but anything's possible! When buying an electrical product I personally never check whether it's been certified by the TUV (or similar), but I guess there are safety regulations regarding such things, and now we all now why. :)

  14. matt Says:

    That was a whole lot of smileys I just used there. Sorry Dan - don't know what your quota is for this blog page - hope I haven't used too many?

    Guess I'm just happy that the week's over at last...

  15. Dan Todd Says:

    Couple of points:
    1. From what I can remember, changing plugs or sockets in any way is unlawful in Australia unless you have a licence. You can legally do so in NZ, but not Australia.

    1a. I think that you can do the work if it is checked/supervised by a qualified electrician.

    2. Having any electrical work performed by an unlicenced party can make your home and contents insurance null and void. The burden of proof is probably on the householder, check your policy.

    3. I had a lecturer at uni who designed one of Japan's biggest power plants. I always found it amusing that he was not allowed to change his plugs or sockets.

    4. The mere thought of the mouth-breathers that I meet doing their own electrical work scares the bejesus out of me. Especially when you consider the mess properly licenced people can make.

    5. Most of the world lets you change your own plugs and socket. Some say that the Australian laws are in place to protect the jobs of electricians.

    6. If doing this is so wrong, why can we still buy the plugs and sockets? I've always been confused by that. You can legally by the components, but you can't use them.

  16. Zero_DgZ Says:

    Working at the hardware store (it's the place that I, you know, work...) we have sort of a running gag that comes around like clockwork every Christmas. Of course we sell lights and hooks and mounts and other related thingamabobs, and of course your normal red-blooded American males are just the sorts of people who come in to buy them.

    Well. Without fail, at least once a week (very often more) we get to play this cryptic game of 20 questions:

    You're looking for a 'plug adpter.' Okay, what kind of plug? An electric plug? (In lower class America, nothing is electrical, electronic, or electricity. It's all "electric." As in 'Hey, the electric is out.' It makes me want to punch people, but then again so many things do. I digress.) Yes, I assumed that. What are you adapting from and to? The thingy that you put into the socket to another one just like it?

    Ah, now you see the game. What homeboy is looking for (though homeboy is seldom articulate enough to express it the first five or six tries) is a male-to-male 120 volt mains adapter (Sometimes female-to-female; yes, mains power in the USA is a wimpy 120 volts).

    The sob story usually goes something along the lines of Husband starting on one end of the house Wife starting from the other, no coordination between the two, and they meet at the middle both holding identical plugs. Fit together they do not.

    Of course, the niggling fact that there is a very good reason such a thing doesn't exist (plugging a duplex outlet into itself with an extension cord is the first the leaps to mind...) isn't the customer's fault, it's OUR fault, and without fail are we railed on about our inadequacy of not stocking such an item.

    Usually I have to explain why very slowly, using small words and simple expressions (electrocution BAD!) to get the point across, and ultimately am forced to give up. See, you're the kind of customer who would already know how to build your own, so I could leave you to it.

    I did once make a male-to-male adapter out of two plugs and about six inches of extension cord wire for a regular customer who I had reasonably confidence would not do anything stupid with it. He ran a local towing/auto repair sort of place, and had a christmas light display in his yard utilizing some hundred-and-fifty-thousand bulbs that was basically a local tourist attraction. It's made the papers on several occasions; I don't think he's burnt his house or display down since I built him that adapter.

  17. Daniel Rutter Says:

    Zero_DgZ: The friends of mine who used to work at Dick Smith Electronics here in Australia always knew they were in for a wild ride when someone came in wanting to buy an "adaption" :-).

  18. matt Says:

    4. The mere thought of the mouth-breathers that I meet doing their own electrical work scares the bejesus out of me. Especially when you consider the mess properly licenced people can make.

    A while back some network technicians were requested to install two jacks in a floor tank in a restricted area at work, and I was given the task of supervising them. Having just run some Cat5 at home and made a mess of it, I told the guys I was looking forward to seeing how professionals did it. What happened over the next couple of hours left me speechless.

    - One technician removed floor-tiles around the edge of the room and got the cable laid there. Then he discovered that the tiles were wedge-shaped (it's a circular room), and the tiles would only fit in the right order/orientation. He spent one hour getting these back in.

    - The other technician pushed a wire-puller down through a conduit under the floor, but was unable to get it to come out the other end. He was also unable to get the tool back out of the conduit, so he ended up sticking the other end into another conduit, and getting that stuck too. At some point in time he managed to get cable pulled through the conduit, but one conduit was still blocked with the cable-puller. He eventually decided to leave it there, and cut it off under the floor. As he cut the fibre-glass rod, sparks fly out of the floor-tank (there're power-points in there too). Not sure where those came from, but as the power sockets are labelled, I check the breaker and it looks okay.

    - Having got the cable run, the two team up to install the jacks. But the sockets they have are a different system to what we've got in our tanks. So they set about trying to get this thing installed anyway. They come up with a workable solution, and one goes off to find a battery-drill. Half an hour later he comes back with a drill-bit, but no drill. Proceeds to try to drill holes in hard plastic with nothing but a 4mm drill bit in his fingers. The other decides to cut up a bit of the tank's existing mounting-plates so that his network sockets will fit in there. This is accomplished with a hack-saw, and much bending back-and-forth of the plate. The result is bent, covered in blood (he cut himself while bending the metal), and the network socket still doesn't fit into it.

    After two hours they got the tank together and we had to vacate the room. The rest of the work (running the cables to the patch bay) was to be done in a patch-room outside of the restricted area, and was done a few days later, once they'd found the key to the patch-room. Of course, they did it when I wasn't around, and so couldn't test the result. A few days later, a user went to use the sockets and found that not only did they not work, but also the power-points in the floor-tank were dead.


  19. Liam Mitchell Says:

    Up until very recently I was a manager in a DSE store (I now work in the electrical industry, not however as an electrician, but I digress) and I feel the need to point out just how common the "adaptor" question is, particularly if your store happens to be in a toursim precinct, which mine was, and you see a large number of tourists (and no offense to any Americans but you guys seem to be the number one offenders here).

    Pleb: "I want an adaptor"
    Sales staff: "What kind of an adaptor"
    Pleb: "You know, an adaptor?" (Pleb now looks at sales staff like he/she is bereft of their senses)
    Sales staff: "What exactly were you seeking to adapt?" (Sales staff is now clenching his/her fists so tightly their knuckles are white)
    Pleb: "A plug."
    Sales staff: "Excellent. What kind of plug?"
    Pleb: "Oh. A power plug."
    Sales staff: "Ah, well you didn't say that at first did you? They're over there."
    Sales staff: "Yes but that would be illegal."
    Pleb: "Can't you do it?"
    Sales staff: "Yes that would be even more illegal, and I'd be awfully tempted to bridge active, neutral and earth together and see just how much your hotel really appreciates your business."

    Then they leave with their "adaptor". The best ones though are the middle eastern males who absolutely refuse not to rewire all their appliances themselves and look about ready to punch you in the face when you inform them that even if you wanted to it's against company policy for you to do it for them.

    Needless to say the "I want an adaptor" customer is the bane of every DSE employee's existance and while it was a little off topic I saw that comment by Dan and just HAD to throw my two cents in.

  20. Jonadab Says:

    magetoo, yes, there *are* things that care about the difference between hot/active and neutral/cold, although most things don't.

    However, the big problem with switching hot and cold (aside from the surprise you're leaving for some fool twenty years later who goes to do some wiring and assumes, being the idiot that he is, that the previous lunkhead did everything correctly) is what happens if you combine it with something that switches neutral and ground. Making those two swaps in series means that effectively you've now got the hot wire switched with ground. Not recommended. The safe half of it is the part about hooking the household ground (which around here is normally wired to the incoming cold water pipe) up to the appliance's hot power wire, which will not effectively power your appliance but also will not do any tremendous harm, at least under normal circumstances. The less safe half of making that switch, though, is that the household hot/active is wired up to the appliance's ground. A lot of appliances run the ground wire to the chassis or metal case. So touching the appliance in such a situation connects your personal body to the full voltage. Extra bonus points if you are standing barefoot on a metal heating/cooling register at the time, or otherwise touching anything that's grounded (such as, for instance, a correctly-wired appliance). Now the AC voltage from the household hot power line is connected to the neutral line on the extension cord and thence to the ground line of the appliance cord, to the chassis of the appliance, to you, and from you to the chassis of the other, correctly-wired appliance that your other hand is touching, which is wired to the household ground. Congratulations, you are now a conductor.

    I am pleased to live in a country where that's normally 110V/60Hz for most wiring. Getting jolted with that is not a comfortable experience, as I can personally attest, but unless you have some kind of heart problem or something it will usually not cause any lasting injury to an adult. Not that I suggest doing it on purpose or anything.

    220V is more worrisome. I know a guy who inadvertently brushed up against a range cable while working in home construction. That's 220V/60Hz, and it left black fang-marks on his arm where the two wires touched him. (I *think* it was a surface burn, so not permanent. Still. And he was lucky in that he brushed against it only quite briefly.) Australia and most of Europe, I am given to understand, operate nearly everything, even lights, at 220V. There are various arguments for and against the higher voltage (the most important of which, in most areas, is backward compatibility with existing infrastructure and appliances), but from a safety perspective I know which I'd rather get shocked with.

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