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240 vac Relay cct

Discussion in 'Electronic Basics' started by MarkMc, Mar 3, 2005.

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  1. MarkMc

    MarkMc Guest


    I'm putting together a cct which will takes a 240vac input and switches
    it via 2 relays to two 24v ac outputs.

    Currently I'm enclosing this cct inside a plastic box. The 240vac
    inputs are via kettle lead connectors in and out. Should I be
    enclosing this inside a metal box instead?

    I'm in the UK, is there any legal stuff I should be aware of for

  2. Perhaps a tad more info on the cicuit ?
    I.e two 240vac coil relays switching 24v or a 240 to 24 tranny that feeds
    the relays which are switched externally etc etc.
    Pretty hard to help without more details although the "kettle" connectors
    doesnt sound really "pretty" :)
  3. MarkMc

    MarkMc Guest

    ok, transistors, driven by PIC microcontroller outputs, drive 12v
    through each relay primary, which then switch each of the two 240v

    I think the kettle connectors are quite neat. One is the normal mains
    lead in, and the two others are output types, which can be plugged in
    as needed (can use one or other, or both together), and saves me having
    to worry about clamping hard-wired leads in to the enclosure box.

    Does that help?

  4. Yup, so your main concern should be the safety aspect of the mains wiring.
    Personally I would use a metal enclosure that was securely earthed by
    bonding the incoming earth lead to it, using a dedicated screw with flat and
    star washers. All outgoing earths would then be attached above this with
    their own nut and washers. It occurs to me that by "Kettle connectors" you
    mean IEC type plugs and sockets (3 small oblong pins all aligned ) whereas I
    am perhaps of another older era where a "Kettle Plug" was called an
    "Appliance connector" and are a lot more bulky and less reliable. I would
    agree that IEC connectors would be good.
    I do not have knowledge of the codes for UK wiring so hopefully others can
    help you there.
    You would also need to arrange for the interface wiring to seperated to
    avoid potential danger should the signal wiring become connected to the
    mains. A little care with wiring the relays should handle that although if
    the 24vdc can be bonded to earth any mishaps should blow the fuse in the
    240vac circuit. Consider the load you are supplying and if its small and the
    source vac circuit has a large fuse it wouldn't be a bad idea to mebbe have
    a suitable fuse mounted in the enclosure.
    Perhaps another approach would be to use thyristors instead of relays but
    they would definately need to be in a metal enclosure to hold down the EFI.
    Best of luck with your project.
  5. MarkMc

    MarkMc Guest

    Thanks for the advice.

    I'll go for a metal enclosure, with the earth leads connected. I'll
    have to think of a way to segregate the user switches and buttons so
    that they can't get touched by any loose mains leads.

    btw. IEC type plugs and sockets is correct.

  6. Rich Grise

    Rich Grise Guest

    You mount them in such a fashion that the operator-accessible bits (switch
    handles, button buttons) are on the outside of the panel, and the electric
    bits (terminals, wires, etc) are on the inside.

    Good Luck!
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