Or you could just wait 'til there's smoke

A reader writes:

Back when Dick Smith still had Dick Smith in the logo and sold more than plasma TVs and pre-paid mobile phones, you could find there a little electrical detector thing made by HPM. I remember seeing it as a kid, but can't now remember what it was supposed to detect. I came across one in a laboratory undergoing decommission early this year, and took it home and plugged it in. It cheerily lit up a red and green "OK"

Satisfied that something was "OK", I left it plugged in in the bathroom to entertain my housemates.

That probably isn't good.

Last week, though, it switched to red and flickering orange, which I suppose means "Not OK". It has stayed like this ever since, but returns to normal in other people's houses. Lacking the manual, I wonder if you knew what this could signify?


PS Manuka Coles supermarket is selling the power meter you reviewed last year, this time branded Arlec (nostalgia!), for $29.90. Power metering for the masses!

I remember those things! They're "receptacle testers" or "outlet testers", thousands of them no doubt still lurk in kitchen drawers, and more refined versions still exist today.

I don't remember the exact wiring inside the old kind, but their basic idea is to light "Not OK" combinations whenever they see something other than the correct socket wiring. They want to see volts on active, no volts on neutral, no volts on earth, neutral and earth not electrically connected, and earth actually doing some earthing. (I think that's all.) Anything else gives you Not OK lights.

(I think these testers only exist in places, like Australia, where standard electrical sockets always have an earth pin, and only work one way around, so even a two-pin plug cannot be plugged in backwards. The USA, in comparison, is full of non-polarised earth-less sockets, so you can't make a tester that can figure out if there's something wrong, beyond incorrect voltage. UPDATE: As commenters point out below, I was wrong here - the States may still have a lot of two-pin either-way plugs, but any slightly modern building should have three-pin polarised sockets.)

If the tester's working properly, the Not-OK combination does indeed indicate a serious electrical problem. It's entirely possible for a building's wiring to originally be OK and then go bad; that rules out the classic "amateur electrician connected the wires wrong in 1978" problem, and if your appliances still work then that narrows it down further, but there are other ways for wiring to go bad. You could have no earth at all any more, for instance; that can have zero effect while everything else is fine, but if a wire comes loose inside your toaster and touches the chassis, then instead of shorting to earth and popping a breaker, it'll just sit there waiting to shock you.

I suppose this could perhaps just be something wrong with the old socket tester, but since it works in other houses I rather doubt that this is the case. But all things are possible, in this best of all possible worlds.

You can look at the socket wiring yourself without greatly endangering your life, by setting a multimeter (a $10 cheapie meter will be fine, as it almost always is) to the appropriate AC-volts range, and sticking the probes into the appropriate pin-holes of the socket.

(Deem usual warnings about how it's not my fault if you do the above after putting the other ends of the test leads in your mouth to have been included here.)

Looking at the socket, here's what the holes should be:

active /   \ neutral

         | earth

Active-to-neutral should give you 240 volts AC (Australia is now nominally a 230VAC country, but I think pretty much everywhere still actually has about 240V). Neutral-to-earth should give you zero (a small voltage here does not indicate a serious fault; capacitive coupling between active and neutral wires can give neutral a few volts with a safe near-zero current capacity). Active-to-earth should give you 240V (or near offer) again.

It's possible, but unlikely, that doing the last test may trip a "safety switch" (ELCB or RCD), since the multimeter will pass a weeny bit of current. This doesn't by itself mean there's anything wrong; it's normal for perfectly safe appliances in the average house to also leak a very small amount of current to earth, which'll use up some of the trip capacity of the safety switch and leave it susceptible to tripping when something, like a multimeter, adds only a little more leakage.

The impedance of a cheap multimeter in AC-volts mode should be a couple of million ohms, so it should only pass a small fraction of one milliamp from 240V. That isn't likely to bother even a twitchy 5mA safety switch, let alone one of the more common 20-30mA ones. But if your $10 multimeter does manage to trip the RCD, just go to the breaker box and un-trip it again.

(If your safety switch trips when it sees a 20-milliamp difference between the current in active and the current in neutral, and stuff in your house is already leaking, say, 17 milliamps in total, then you can get irritating "nuisance tripping" at random moments. This may be curable by a process of elimination, finding the one appliance in the house that contributes most to the problem; if that doesn't work, the annoying safety switch may be trying to tell you about a real wiring problem.)

A safety switch may also instantly trip when you plug an outlet tester in, because the old-style three-lights tester comes from a time before safety switches, and inherently passes a small current between pins that should not normally be connected. Modern outlet testers are more sophisticated (and more expensive); they typically have an "RCD Test" button, and only pass current from active to earth when you press that button.

If I were you, the first thing I'd do would be to unplug everything unpluggable, and see if the outlet tester returns to happiness. If it does, plug things back in one at a time until the problem recurs, then unplug the offending appliance, cut its cord off and dispose of it. (Or get it fixed, if it's your hundred-inch plasma TV.)

If unplugging stuff doesn't help, and especially if the above quick multimeter test reveals a problem, it's Qualified Electrician Time. If you're lucky, the fault is in the breaker box or the Lovecraftian wiring that lurks behind it. If you're less lucky, the problem's in the walls somewhere. Either way, it's something you need to attend to, lest you get zapped, or awaken to a thrilling housefire.

UPDATE: Modern equivalents of the old socket-tester do exist. Here's one with an Aussie plug that only costs $AU21.95.

13 Responses to “Or you could just wait 'til there's smoke”

  1. jnz Says:

    I think your description of the situation in the USA is a little misleading. There are plenty of old non-polarized sockets out there in old buildings from the "dark ages". But all new construction and new work in old buildings uses the newer 3-prong outlets. And testers exist for these. Building inspectors do check this and won't sign off unless the tester indicates things are OK.

  2. jstanley0 Says:

    jnz beat me to it by a second. I haven't seen non-polarized non-earthed sockets in any building younger than fifty years.

    (A quick search says unpolarized receptacles have been prohibited in new construction since 1962. Source: http://en.wikipedia.org/wiki/Electrical_outlet#Types_in_present_use - [citation needed] on that particular point.)

  3. Daniel Rutter Says:

    Sorry about that - I've added a bit fixing my error.

    What a crazy futuristic world this is. Next, you'll be telling me that you can buy a toaster in the UK and just take it home and plug it in, without having to use a screwdriver at any point at all!

  4. Alex Whiteside Says:

    On the subject of mains electricity, and deceptiveness...

    Looks like it would work in the UK (it has HK plugs which are compliant with BS-1363 I believe, and it's the right kind of GSM).

  5. Red October Says:

    As a child I collected old electrical fittings. In houses built as far back as the 20s polarized sockets were common. Most everything else was not polarized, extension leads, most actual appliances, etc. Most of the sockets were of the "T-slot" type and could supply 120 or 240 volts (rated 120VAC, 15A, 240VAC, 10A). It's an unusual socket, at least in my experience, that is not polarized. Some exceptions are the sockets on overhead lamp fitings (Something that may shock those living abroad is that in the US it is very common for a procelain overhead light fitting to have an integral electric socket, probably relics of the days when light sockets were the only common power points in a home and these would be seen as upgrades. Early variants are unreliably polarized; modern variants are earthed and still sold today, and even installed in new construction, usually in places like basements where conventional outlets are uncommon.) and the integral plugs on things like bathroom light fixtures (to facilitate the connection of electric shavers, blow dryers, etc, as even when plug sockets became commonplace, they were not in the bathroom until the 60s or 70s) and stoves. There is an annoying trend here for things that don't need to be polarized (lamps, for instance, double-insulated electric appliances, etc.) to have polarized plugs for no good reason, making old octopus taps, extension cords, etc, hard to use. Another device that may unsettle the rest of the world are the ground cheaters; devices that austensibly allow a 3-pin grounded plug to go into an ungrounded receptacle, typically having a pigtail or flange to allow it to connect to the plate screw (which must be earthed but sometimes is not). When earthing began to be recognized as useful, some interesting experiments were made, including using a plug type identical to the Australian plug! Many houses have earthed receptacles in the kitchen but not elsewhere.

  6. Hobie-wan Says:

    My previous living arrangements (I'm in the US) were in some old converted slaves quarters that were pretty ancient. None of the plugs were grounded and the entire electrical system in the place was scary. As I recall there were only 2 or 3 old circuit breakers in a very rusty and weather worn box outside for the entire 2 bedroom apartment. The wiring inside the walls, aside from being ungrounded, was old rotting cloth insulated *cough* wire, and I swear I saw some aluminum when putting a ceiling fan in my room.

    No wanting my PC to be unprotected in the unfortunate time I was living there, I took it upon myself to at least ground my PC. I bought one of those horrible 3 to 2 adapter jobbies with the tab, then ran some (house wiring spec) wire from the tab out the window to an earth stake I found in the bushes. The 'ground ok' light on my power strip came on, so I assumed it was all right.

    Man I was afraid of dying in a fire in that place.

  7. n17ikh Says:

    @Red October:
    There is actually a good reason for lamps to use a polarized plug (in the US at least). We use Edison screw connectors, so there's a great big surface inside (the female screw thread part) that catches errant fingers and sometimes almost sticks out a small bit from the insulating surface surrounding it. It's a bit safer to have the hot side connected to the relatively small connector at the bottom of the socket instead of the big screw thread at the edge of it. If we used bayonet connectors, it wouldn't matter so much.

    Also, if you folks think cloth wiring is scary, you should check out knob and tube wiring, which is pretty frightening. However, as anyone who collects antique electrical appliances knows, there are some pretty dodgy things around. My mom has (and uses!) a toaster that has a nice chrome-and-stainless-steel chassis and horizontally-strung nichrome wire under a clever basket to toast the bread. You flip the bread manually, and it's a neat toaster, but the nichrome wire is of course bare and sometimes falls off the porcelain posts it's strung around to contact the surface of the toaster (which, by the way, is wired to the wall with a nice cloth and India-rubber plugset), leaving only a tiny set of bakelite handles on the bread-basket between the user and a nice shock. Of course, when it was manufactured, there was no real electric code. It probably was plugged into one of the aforementioned porcelain light-fixture sockets.
    Also: Dan, your comments system needs some sort of preview button. This tiny little window is no place to write up a comment of any real length.

  8. frasera Says:

    yea basically i've never seen a 2 prong only us socket ever in my life. i know they exist in very very old homes perhaps, but i've never seen one personally. i've used the plug wiring verifying doohicky when replacing my house recepticals with the prettier designer or whatever more angular looking ones. the only place where plugs are varied is the 240 appliance connections, there are plugs of different types or simply a wiring box, because well, appliances tend to be installed by installers so it doesn't matter.

  9. Red October Says:

    The "Lamps need to be polarized because of the Edison Screw base" argument is one I've heard before but still can't come to tearms with. The metal part shouldn't stick out of the socket at all. Such a socket is faulty. There should always be a paper insulator. Once the bulb is screwed partway out, the circuit is broken even if the fitting in question is energized. Only a cirtifiable idiot puts his digits into a possibly-energized electrical fitting of any sort.

    About the most unsettling fitting I have is a light socket that is quite simple in its construction; a single piece of porcelain with flanges to put screws through, and the two terminals exposed to the world on the sides. This fitting was removed from service in the late 1990s! I've seen some pretty scary stuff done by the homeowner, but nothing so bad simply in its own existance as that. The same house had a mix of Greenfield cable (Otherwise known as BX armoured conduit/cable -it has a spiral armour jacket that serves as an earth) and very early NM (nonmetalic) cable that had a sticky black coating and, IIRC, no earth at all. Through some miracle, however, every actual receptacle had earth available (I tested them all; didn't bother with the lights). One final thing of note; very many heavy appliances like ranges and dryers get a 240V split phase system with only three pins; two hots and a common return which also serves to earth the circuit! This is contrary to all other practice in this country.

  10. magetoo Says:

    It's an unusual socket, at least in my experience, that is not polarized. Some exceptions are the sockets on overhead lamp fitings [...]

    And here in Sweden, all sockets and plugs are non-polarized. Except those that are involved in lighting. (round, often completely symmetrical, three-prong - some trial and error is often needed)

    It is my impression that all of proper Europe uses Schuko and Euro plugs now. That's one vote against rarity of unpolarized sockets I suppose...

    And I'll second the need for a preview function.

  11. Mohonri Says:

    @n17ikh - One of my coworkers lives in a 1930's house, and just had all the knob-and-tube wiring redone (at considerable expense). That is indeed some very intimidating stuff, but he brought a few pieces for show-and-tell, and I was impressed with how well the insulation has held up.

  12. Red October Says:

    Cloth insulated K&T wiring can last quite well indeed, if it is not overloaded. As it passes through the air it can easily dissipate heat and doesn't need to be as thick as other types of wiring. No insulation should be installed around it, which can complicate insulation of upgraded construction, as the plaster-and-lath walls of the day were quite insulating of their own, but the modern wallboard types are less so, and often unknowing homeowners install insulation over the stuff and result in overheating. In the US, for refference, it is ostensibly legal to perform your own wiring work.

    The worst such job I saw was all in a house that has since been plowed under. Old, perhaps the 30s, construction, upgrade in the 40s to finish the attic. The upgrade drew the power for the upstairs entirely from the kitchen lighting drop, so if that fuse blew the entire upstairs, the kitchen, and several other areas were plunged into darkness (The code of the day stated that no one room could be fed by a single circuit, so that a failure would not plunge an area into total darkness). The kitchen was on the way to the cellar where the fuse box resided. Some well-meaning idiot had installed "tamper-proof fuse adaptors"; little threaded tubes that allowed only a certain type of fuse to be installed (all our regular fuses use an Edison base), ostensibly preventing over-fusing but also preventing installation of the very useful mini circuit breakers.

  13. richardw66 Says:

    I used to have one of those socket testers myself - handy gadget.

    I believe it's just a neon from Active to Earth and from Active to Neutral for the OK lights.

    A neon between Earth and Neutral for the not OK.

    There's nothing more dangerous than discovering you are working on a switched neutral system when you think you are working on switched active. I once blew a Miele washing machine controller once by making this mistake, very, very expensive.

    I have also seen someone nearly get fried whilst working on an external hard drive case that was switching the neutral line, thereby rendering the whole circuit live when switched off.

    I also got caught out myself when fixing a ceiling light fitting after turning off the switch, but the circuit was active due to some rather old wiring.

    Polarisation is important!!! Even when you believe that sensible people would stay away from the active.

    Not all residents of houses are electrically certified, and insulation will not always be fully intact for the life of the device.

Leave a Reply