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Testing a standard lamp

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  • 15-11-2021 10:13am
    #1
    [Deleted User]
    Posts: 0 ✭


    Hello all.

    Silly question 🤐....

    I have a basic multimeter: Parkside 15 euro job. Any advice on how I could test if a desk lamp has any current running through it? Safe to use a multimeter on a lamp plugged into the mains supply?



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    #2
    10-10-20
    Registered Users Posts: 7,169 ✭✭✭10-10-20


    Don't use the meter to detect current as that would be dangerous especially with a meter with an unknown isolation capability - use the meter instead to check the resistance along the electrical paths.

    Disconnect the lamp from the mains completely. Remove the bulb (especially as newer LED bulbs don't have a low resistance like filament bulbs). If there is an in-line switch, switch the lamp on. Use the resistance measurement on the meter to check from each plug pin to the internal connections for the bulb. If you have a bayonet connection (BC) bulb then each pin on the plug has to run to either of the bulb pins - or if you have a Edison Screw (ES) then to the bottom pad and the surrounding thread-body. You're looking for resistance <1 ohm for both tests.

    If the lamp has a touch control, then none of these tests will work and the lamp may not be serviceable.



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    #3
    [Deleted User]
    Posts: 0 ✭ [Deleted User]


    https://www.boards.ie/discussion/comment/118168379#Comment_118168379

    Thanks @10-10-20 . I could have been sporting a new hairdo if I plowed ahead ⚡️!


    So in essence, I'd be checking the resistance value of the metal components of the lamp?



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    #4
    10-10-20
    Registered Users Posts: 7,169 ✭✭✭10-10-20


    https://www.boards.ie/discussion/comment/118168865#Comment_118168865

    When you say "metal components", I don't mean the metal of the lamp itself - just the metal within the bulb socket, ok?

    You'll be testing to see if the power can get from the plug to the bulb contacts by measuring the resistance of the Live and Neutral copper wire from the plug to the bulb socket. If that multimeter has a basic continuity tester, it should beep when you have a good connection. Test it out by connecting both probe leads together and see if it beeps.

    Also don't for get that lamps should be fitted with a 3A fuse at the plug socket, so also test this with the continuity tester to see if it's good or not. That should actually be the first (and easiest) test.



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    #5
    Bruthal.
    Registered Users Posts: 209 ✭✭Bruthal.


    Depends what ye are actually trying to do? Measure current? Check continuity?



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    #6
    [Deleted User]
    Posts: 0 ✭ [Deleted User]


    https://www.boards.ie/discussion/comment/118168951#Comment_118168951

    Thanks @10-10-20 . Gotcha! So I use the continuity functionality of my multi-meter on the bulb contacts, which in turn determine the resistance of the live and neutral wires.


    Yeah, the fuse would be a good start.



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    #7
    [Deleted User]
    Posts: 0 ✭ [Deleted User]


    https://www.boards.ie/discussion/comment/118168960#Comment_118168960

    I guess a bit of both. The lamp no longer seems to work. Tried a new bulb and a new fuse, but no luck.

    If the wiring is the issue then requiring might fix the lamp. Lamp is over 15 years old.



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    #8
    Antenna
    Registered Users Posts: 2,317 ✭✭✭Antenna


    https://www.boards.ie/discussion/comment/118170230#Comment_118170230

    What sort of switch is on the lamp? That may have failed.

    If its just a basic on/off switch (not a touch sensitive one, or a dimmer) your multimeter's resistance/continuity would easily test this (or bypass the switch if you can and see what happens)


    I'm assuming the bulb is mains voltage (230V) ?

    If its a 12V one, its important to say so, as its transformer might have failed.


    You say that you tried a new fuse, but did your multimeter show that the existing one was blown???

    BTW the arc that can briefly happen inside a 230V filament bulb when it blows can sometimes also easily blow a 3A fuse.



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    #9
    [Deleted User]
    Posts: 0 ✭ [Deleted User]


    https://www.boards.ie/discussion/comment/118179499#Comment_118179499


    What sort of switch is on the lamp? That may have failed. A basic on/off switch.

    If its just a basic on/off switch (not a touch sensitive one, or a dimmer) your multimeter's resistance/continuity would easily test this (or bypass the switch if you can and see what happens) Thanks, I've heard of the continuity test.


    I'm assuming the bulb is mains voltage (230V) ? Correct

    You say that you tried a new fuse, but did your multimeter show that the existing one was blown??? We, tried the working fuse and non-working fuses on another device. Both fuses had same status.

    Thanks for the above. I'll run the continuity test and maybe a rewire is necessary. Hopefully, I can buy wires wrapped in an insulated case and simple screw wires in the plug terminals.



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