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Re: Internal wiring of USA v UK mains plug

Discussion in 'Electronic Repair' started by N Cook, Jun 27, 2007.

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  1. N Cook

    N Cook Guest

    We have no choice in the matter, by law, we can use 1,2 or 3 amp fuses
    inside these plugs but thats the only choice

    The USA cannot have the equivalent of RoSPA (Royal Society for the
    Prevention of Accidents), AFAICS none of the USA ones have child preventers
    on them unless the mouldings on the wall outlets preclude that eventuality
    of small fiongers touching both pins.
    The other notable difference is the insulated pins that have been necessary
    refinement, again by law, for 20 years or so
    You can just see the orange plastic bits extending up the brass pins on the
    first pic on this wiki and the black bits on the one lower down on
    The phase and neutral pins on modern plugs have insulated bases to prevent
    finger contact with pins and also to stop metal sheets (for example, fallen
    blind slats) from becoming live if lodged between the wall and a partly
    pulled out plug. A downside to this prong insulation is that it may
    contribute to damaged sockets not making good contact with the prongs, which
    may even melt the latter. No such problems exist with healthy sockets.

    as an aside someone told me that per million houses there are more house
    fires in the USA due to wiring faults than any other country, partly due to
    a lot of timber construction and partly due to the higher current for a
    given KW of power transfered - is that the case?
  2. TT_Man

    TT_Man Guest


    Have you seen the way they connect their wires? They just twist them
    together and put a plastic cap over the bare wires!
    Multiply that by double current and it's no wonder they have fires :)
  3. Tam/WB2TT

    Tam/WB2TT Guest

    All heavy loads are connected across 240 Volts. 120 is basically used for
    things that can be moved from room to room. There seem to be two main causes
    for electrical fires in the US. One the improper use of extension cords; for
    example, a 10 foot length of 5 amp wire with a refrigerator and microwave
    plugged in at the far end. This comes about because older houses and
    apartments tend to have an insufficient number of wall outlets. Two, there
    was some problem with houses built about 30 years ago that uses aluminum
    wire; these require special connection methods. When a home owner replaces a
    switch or an outlet with a standard device, you have problems. Most home
    owners here tend to do their own electrical repairs.

    I think there is an inherent safety factor in a system where neither side of
    a 240V circuit is more than 120 V above earth potential. Never heard of a
    person being electrocuted who was not standing, or otherwise submerged, in
    water. This costs money. For instance the wiring to an electric clothes
    dryer will have two 20 Amp hot wires, a 20 Amp neutral wire (from center tap
    of transformer), and a 20 amp earth ground wire connected to a cold water
    pipe or ground rod. In some localities, the neutral and ground wires can be
    tied together at the appliance. I think the only reason for the heavy
    neutral and ground wires is to make sure the circuit breaker trip in case of
    a short. As recently as about 20 years ago, a much smaller earth ground wire
    was used.

    The electric use meter must be more expensive than an unbalanced single
    phase one.

  4. Neil

    Neil Guest

    A colleague in Maryland said that he'd attended a safety talk from what
    sounded like the equivalent of a Health and Safety guy, who advised that the
    best way to reduce the probability of fire in the house was to rewire the
    kitchen sockets using decent ($3) sockets rather than the $0.25 ones the
    builders use. Apparently it's something to do with quality of the bits of
    bent metal that make contact...
    And he also advised to not unplug appliances if possible, since that wore
    out the sockets faster.
    Out of curiosity, I bought a double socket for $0.44 at the local Walmart,
    and was somewhat dismayed by the apparent lack of robustness.
    No comparison with our 230V 13A sockets, but maybe that's why they are
    around $4+ each instead.
  5. Tam/WB2TT

    Tam/WB2TT Guest

    They are called wire nuts, and contain a threaded metal insert. Sort of an
    inverse of a self tapping screw. I understand the hesitance, but they don't
    seem to be a problem

  6. Ron(UK)

    Ron(UK) Guest

    We used to have a similar thing but made of ceramic, called a scruit
    (sp?) (pronounced screw-it) I understand that they may be outlawed these

  7. Gary Tait

    Gary Tait Guest

    Actually a typical US clothes dryer uses a 120/240V 30A circuit.
    And the ground wire always connects back to the services neutral, where
    things are grounded with rods and/or plumbing.
    They way is was, is that it was permitted to run just a grounded
    conductor (neutral) to the appliance, and bond that to the case.

    Since 1996 or so, that has been prohibited, so separate neutral and
    grounding conductors must be supplied to a 120/240V appliance.
    For the safety ground, yes. For neutral it is assumed, to the terminals
    in the appliance, that the appliance could draw the full current on the
    If you mean the US ones, 2-wire 120/240 ones are the norm, so are made
    in quantity enough not to be expensive.
  8. Eeyore

    Eeyore Guest

    I fixed a Weller TCP iron a couple of weeks back that was running cold. A 'wire
    nut' inside was loose and a connection to the element had become iffy.

  9. b

    b Guest

    Sounds dodgy!

    I've spent time in the US and Japan, and I have to say that those flat
    blade sockets are an atrocious design. They suffer sloppy fit problems
    very easily . Those countries don't seem to have switched wall sockets
    either, which the Uk standard has, so you get more arcing if plugging
    in live equipment (which degrades the contacts even further).
    The UK plugs are more complex, and expensive, but a damn sight safer
    and a lot more sturdy and resist wear better -only ever had to
    replace one or two fittings over the years.

    I suppose all this is because it is a more recent standard - like the
    German PAL TV system - which, since it was introduced later, had the
  10. John Larkin

    John Larkin Guest

    Most US electric meters, at least the electromechanical kind, have one
    voltage coil (240 volts, l-l) and two current coils, one in each of
    the 120 volt phases. That computes power based on an assumption of
    voltage symmetry, usually a reasonable bet.

  11. James Sweet

    James Sweet Guest

    Done correctly, a quality wire nut is a very secure and long lasting
    connection. It's not simply a plastic cap, but a plastic casing over a
    threaded springy metal insert which grips the wires very well. I have some
    UK terminal blocks, and the problem with them is that there's no mechanical
    bond between the wires, the contact point is small, and they can and do work
    loose or corrode over time. They generally are ok, but neither method is
    greatly superior to the other.

    The double current isn't really much of an issue, our large loads are 240V
    too, it's handy to have both voltages readily available.

    You can get quality US style receptacles, problem is they're expensive so
    few houses come with them. I like many things about the UK plugs, but the
    thing I don't like is they're *huge* so things like power strips and
    multi-gang outlets are really cumbersome.

    Having discussed this in length with a friend in the UK, we've both come to
    the conclusion that both systems have many advantages and disadvantages and
    neither one is a clear winner.
  12. N Cook

    N Cook Guest

    Could someone direct me to pics of the 2 different types of plug/socket
    system used in the USA to differentiate for medium and high power use, I
    didn't even realise 220 or 240V was used residentially anywhere in the USA.
  13. There are several kinds depending upon the current rating and if 120
    volts is used too. Before 1996, the ground pin was also used for neutral
    for things like clothes dryers that had a 120 volt motors and timers and
    240 volt heaters. I think that practice was stopped in the late 1970's.

    In 1996, it became illegal. If your device has a mixture of 120 and 240
    volt components, you need to have a four wire plug. I left the U.S. in
    1996, so I've never seen them.

    The simplest kind is used for air conditioners and is similar to a 120
    volt grounded plug, with two flat blades and a rounded ground pin below
    them in the middle. The difference is that the flat blades are the same
    size and are horizontal instead of vertical.

    I remember walking into an electronics store in SoHo (in Lyle Street?)
    around 1983 and talking to the owner for a while. We got on to discussing
    the differences in power cords and he showed me the 240 volt cords
    they sent to the U.S. He was surprised that I was familar with them.

    He also showed me a catalog from a U.S. company called Herbach and Rademan
    that sold surplus electronics. He imported items from them. It was
    my turn to be surprised, I lived less than 2 miles from them and was
    a frequent customer. :)

    By 1989, the store was gone, it had become a Chinese grocery. In 2001 I
    was given a stack of U.K. radio magazines and an article about the
    store was in one of them. It was written by the nephew of the man
    I spoke to. Unfortunatley he had no pictures of the store near the
    end, and although I took many photographs of London that trip, I
    never thought to take one of the store or his uncle. :-(

  14. ["Followup-To:" header set to]
    Just to add more aspects to this discussion. In Germany, practically all
    houses have 400V three-phase electricity, which is three 230V phases 120°
    degrees apart. So all the normal 230V outlets are just a single phase out of
    those three plus neutral.

    Big appliances in a fixed location like electric ovens and water heaters get
    all three phases but are not required to use them in balance.

    The nice thing about this is that if you want to set up a workshop in your
    house, all you need is some extra fuses and cable and a couple those nice
    big, red CEKON sockets.

  15. b

    b Guest

    Leaving aside the joining wires/terminal blocks issue, on the subject
    of the plugs and sockets, the UK one to me is superior in many ways.
    1. fused plugs.
    2. cord grip in plugs
    3. screw terminals in plugs -no wrapping wires.
    4. ALL receptacles and plugs have earth pin.
    5. 3 prong design means a better fit (they don't waggle about at all)
    6. much thicker pins - handle more current, do not bend, and seem to
    resist arcing damage better.
    7. switched sockets

    The US /japan one only has the advantage of compact size, personally I
    can live with a bigger plug if it means better performance. I couldn't
    care less about cosmetic aspects!

    just my tuppence' worth. -B.
  16. Ok, I'll conceed that one, but only 50%, after all, how many people
    put a 16amp fuse on a .5mm cord?
    You can get them in the U.S. I occasionaly use them here for 120
    volt equipment (I brought a few items with me) and had a friend
    bring me some LEVITON (high quality plugs) from the U.S. They
    ave execelent grips on them.
    The Leviton plugs have them too. I'm not sure they are an advantage,
    the gripping area is the area of the screw shaft,not the circumfrence
    times the area of the wire surface, a lot smaller.
    Cut me a break. Since around 1960 all of the outlets in the U.S. have
    grounds. In the U.K. you can buy appliances with 2 condoctor cords
    with two plug pins that can usually be forced into U.K. outlets.
    They are supposed to be for export to the E.U. but they are sold.

    Many of the appliances sold here come that way too, but I must be
    the only person who cuts them off and puts three pin plugs with large
    grips on them. I also write the name of the appliance on its plug.

    It does not make an difference electricaly, the appliances come with
    two conductor cords and I don't replace them.
    See above.
    That's a big problem here. Many appliances use 15-16 amps (at 230 volts)
    and come with the smaller round plugs which are rated at 16 amps, but
    not for continuous duty. When we moved into this appartment, all of the
    outlets had burnt "hot" pins because the previous tenants plugged
    high current heaters into them.

    I replaced the outlet for our oven with an airconditioner plug, which
    except for the round pins looks like a U.K. plug. It's no longer
    used we replaced it with a gas oven.

    7. switched sockets

    Maybe. only good if they are not at floor level.

    One advantage we have here in Israel is that all new construction
    requires a GFI on all outlets. Usually it's BEFORE the main
    circuit breaker.

    As someone said earlier, it depends upon how much you pay. If you
    buy cheap junk, you get cheap junk. :)

  17. 13 amp is the largest plug top fuse. And all flex these days is such that
    it will blow a 13 amp fuse in event of a short - to allow for the fact
    that householders won't use the correct fuse.
    You've no choice in the UK - all plugs must conform to the BS standard.
    One without a cord grip wouldn't.
    No you can't - legally. With the exception of shavers or toothbrushes etc
    designed to fit a transformer isolated bathroom outlet, everything must be
    fitted with a '13 amp' plug with a suitable fuse.
    Well if you reach down to plug/unplug you can operate a switch at the same
    time. Most do as it's sort of bred into them through habit - most outlets
    have always been switched in the UK.
    The usual modern way here is to have a split load consumer unit. One set
    of MCBs protected by an RCD and one set not. The non protected used for
    fixed loads like cookers and water heaters where slight leakage might
    cause an RCD to trip. But we seem to be moving to one RCBO (RCD and MCB
    combined) per circuit.

    In general it's not possible to buy poor quality plugs and sockets in the

    This is one example of the bottom end price wise, but will give good
    service for years.

    Of course you can pay several times that much for chrome etc finish
  18. Tam/WB2TT

    Tam/WB2TT Guest

    Electric clothes dryer, stoves/ovens, and permanently installed air
    conditioners are only available in 240 V versions. Also, larger sizes of
    electric space heaters. The first three are probably more likely to be wired
    in directly to a junction box than to use a plug/socket. There are several
    incompatible types of 240 V plugs. All are huge, bigger than the UK plug,
    and expensive.
  19. Guest

    Well, much of the "fires" due to faulty wiring are because we have
    *had* wiring as a general condition in most houses since the early
    1900s, so after 100 years or so it gets a little tired, and when
    overloaded can fail. Of course, 100 years ago, y'all had very nice
    green lawns and gorgeous buildings.... but little electricity other
    than the very wealthy. Other fires are due to just plain idiocy on the
    part of users, such that would occur here, there or anywhere else.
    Very damned few fires are caused by properly utilized wiring even if
    100 years old.

    As to wire-nuts, what would you propose? Per the code, they must be
    enclosed, the expectation is that the wires are first twisted
    together, then the nut is attached, and the internal threaded section
    is spring-loaded. Are you seriously telling me that wire-nuts are not
    permitted in your country?

    De gustibus non est disputandum. Electricity has been working for us
    over here a good deal longer than it has been working for you over
    there. The typical poor-man's rowhouse (900 sf, 100 sm) in
    Philadelphia has been wired since 1913. Parts of NYC have been wired
    since the late 1800s...

    On the other hand, there is something to be said for observing the
    experiences of others for 50 years or so before taking the plunge...
    Cell phones are a similar item. The US started Analog, only slowly
    went digital because of legacy issues, Europe dropped the first nearly
    10 years of teething, the Middle East and third-world went right to

    Peter Wieck
    Wyncote, PA
  20. You're not saying there is 100 year old wiring still in use?
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